Archive for the ‘Running Mechanics’ Category

The big debates of the past decade: 2) shoe design

February 24, 2014

For almost a decade many runners have been captivated by the issue of running shoe design – a preoccupation fuelled two opposing factors.  On the one hand padding is expected to provide protection and in particular, provides shock absorption attenuating the impact of foot-strike.  On the other hand, there is the allure of the idealistic notion of barefoot running – based at least partially on the rational argument that if our distant ancestors survived by persistence hunting, the human frame must be well adapted to barefooted running.   These opposing influences have led to fluctuating enthusiasm for fashions ranging from barefoot (or minimalist shoes such as the Vibram Five Fingers) to the heavily padded Hoka one-one.

In addition to these two opposing influences there is the issue of the effects, either helpful or harmful, that shoes might have on the twisting movements that occur at the joints of foot and leg. Most notable are the compound motion of pronation occurring at the forefoot and ankle that allows the foot to roll inwards transferring weight onto the medial longitudinal arch as the leg is loaded during stance; and the inwards bend of the leg below the knee (varus deformation) that places pressure on the vulnerable medial aspect of the loaded knee joint while also dragging the ilio-tibial band towards the lateral femoral condyle.  Although pronation is a natural movement, shoe companies have placed strong emphasis on the potential dangers of over-pronation.  To prevent this, they have marketed motion control shoes with a medial post, a structure embedded in the medial side of the shoe that arrests the inward roll.  This affects not only the impact absorbing capacity of the foot, but also modifying the varus torque acting at the knee.

Ethics

The question of high technology shoe design also brings with it the issue of the ethics of unfair technical enhancement of natural ability.   While this ethical issue can only be dismissed entirely by adopting barefoot running, it might be argued that in the modern man-made environment, denying at least a modest degree of protection would be unreasonable.  In principle there is a difference between basic protection and the overt assistance provided by embedded springs such as in the Spira.  However, once any layer of fabric is interposed between foot and ground, there is a continuum of assistance provided depending on the elastic properties of the material.   Nonetheless, most runners accept that the assistance provided by the bulk properties of a compressible material primarily designed for protection against either shock or penetrating injury is reasonable.

Cadence and foot-strike

The protective effect of shoes is clearly demonstrated by two automatic responses seen in most habitually shod runners when they change to barefoot running.  Self-selected cadence increases leading to decreased length of airborne time during each gait cycle, thereby decreasing the magnitude of the vertical force required to get airborne.   Furthermore, as discussed in my recent post on style, foot-strike tends to change.  The investigation led by Daniel Lieberman of Harvard University indicates that barefoot runners are more likely to adopt a mid-foot or forefoot strike rather than the rear foot strike typically seen in about 75% of shod runners.  This change in foot strike abolished the potentially harmful sharp rise in vertical ground reaction force that is generated by heel striking.  Nonetheless, it is noteworthy that avoidance of rear foot strike is not necessarily the case in habitual barefoot runners.  For example the study of north Kenyan habitual barefoot runners by Hatala found that 72% were heel strikers at their self-selected endurance pace, though the majority landed on mid or forefoot when sprinting, when vertical forces are greater.

As discussed in the post on style, there is little evidence that fore-foot strike is more metabolically efficient whereas several studies actually show rear-foot strike is most efficient at low speeds.  The situation with regard to risk of injury is mixed, with greater risk to knee with heel strike and greater risk to structures around the ankle with forefoot strike.  The balance of risks favours a mid-foot strike. Therefore, a shoe style that allows this is preferable.

Joint torques

Kerrigan and colleagues reported that the torques acting at ankle, knee and hip occurring in runners wearing Brooks Adrenaline shoes were increased in comparison with barefoot running.  The Adrenaline is described as a neutral shoe, meaning that it is not designed to strongly inhibit pronation, and has midsole thickness ranging for 24 mm at the heel to 12 mm at the front.  The increases in torque when shod were especially marked for knee varus (increased by 38%); knee flexion (36%) and hip internal rotation (54%) around mid-stance.   Only a minor portion of these increases in torque could be accounted for by the lower cadence of the shod runners.

Knee varus places stress on medial aspect of knee joint at a site especially prone to osteo-arthritis.  It also drags the ilio-tibial band towards the lateral femoral condyle increasing the risk of iliotibal band syndrome.  Knee flexion torque flexion places stress on patella-femoral  joint and increases load on patella tendon and quads.  It should be noted that tension in the patella tendon at mid-stance  is not necessarily bad, as it would be expected to increase the eccentric loading of the quads and facilitate the upward drive of the body that occurs after mid-stance.   Similarly a moderate degree of internal rotation of the hip is required as the pelvis rotates around the hip joint during stance, so a torque promoting internal rotation torque is not necessarily bad, though it is noteworthy that some runners do develop osteo arthritis of the hip.

The heel-toe drop

Elevation of the heel relative to the toe is the most likely explanation for the additional knee flexion torque revealed in Kerrigan’s study of joint torque at the joints. Furthermore despite providing padding, the presence of a bulky heel makes it difficult to avoid localized impact at the heel, and thereby make a substantial contribution in the rapidly rising spike of vertical ground reaction force observed in heel strikers.  As shown by Zadpoor, a rapid of rise of vertical force increases risk of injures such as tibial stress fracture.  Thus, it would appear that shoes with minimal or no drop from heel to toe that allows initial contact further forwards might  be safer, and will tend to be lighter.

An interesting alternative is the Healus, a shoe without a heel.  A slanted sole ensures that the runner avoids heel contact but instead makes contact via a well-padded mid foot.   Force plate data demonstrates that it abolishes the initial spike in vertical ground reaction force.  The padding under midfoot provides maximum protection when vertical ground reaction force is at its peak.  However, despite an endorsement by former European 5,000m record holder Dave Moorcroft , it does not appear to have achieved much popularity, possibly because it is produced by a small company.

Ankle and forefoot motion control

The inward rolling of the foot that occurs with excessive pronation has several potentially adverse consequences.  The ankle tends to be displaced towards the midline thereby increasing varus deformation at the knee, enhancing risk of iliotibial band syndrome and perhaps also osteo arthritis of the medial aspect of the knee joint.   The medial longitudinal arch of the foot is flattened increasing tension in the plantar fascia increasing risk of plantar fasciitis.  Thus, in runners with excessive pronation, a shoe with a medial post that limits pronation might be beneficial.  However it should be noted that Kerrigan observed increased knee varus torque in shod runners relative to barefoot.  The Brooks Adrenaline is a neutral shoe but nonetheless has a modest medial post and hence it might appear surprising that there was increased knee varus torque.  However the shoe had not been matched to the specific needs of individuals.  It is plausible that the one consequence of being shod was that individuals lacked the sensation and freedom of movement within the shoe required to produce optimal adjustment of the motion at the ankle according to their individual needs.   It might be argued that at least for non-injured runners, that light weight shoes or bare feet providing the freedom to adapt the ankle and foot motion according to individual needs and changing surface conditions, would be preferable.

Nonetheless, there is evidence that customised orthotics designed specifically to control ankle motion for each individual can reduce pain in runners with an established problem.  For example, Maclean and colleagues studied the effects of 6 weeks use of customised orthotics in a group of female recreational runners (15 to 40 km per week) who had a history of overuse running knee injury in the 6 months leading up to the study. The intervention decreased pain significantly and led to significant decreases in maxima for ankle inversion moment and angular impulse during the loading phase, impact peak, and vertical loading rate, though the effects at the knee were complex

Efficiency

Because the shoe is at the far end of the swinging leg, its mass makes a relatively large contribution to energy cost of repositioning the leg during the swing phase.   However, there is growing evidence that at least a small amount of padding brings a benefit that compensates for the additional weight.  Franz and colleagues from Roger Kram’s lab in Colorado compared oxygen consumption during running barefoot with that when wearing lightweight cushioned shoes (approximately 150 gm per shoe) in 12 runners with substantial barefoot  experience, running  with midfoot strike on a treadmill.  In additional trials to determine the effect added weight, they attached small lead strips to each foot/shoe (150, 300, and 450 g).   They found that in the absence of added weight there was no significant difference between shod and unshod running.  Adding weight led to an increased metabolic cost of 1% for each 100 gm of added weight.  When adjusting to equalise mass in shod and unshod condition, shod running had ∼3%-4% lower metabolic cost.

In a further experiment for the same lab, Tung and colleagues measured the metabolic costs of  barefoot running  on an unpadded treadmill and after adding strips of padding of either 10mm or 20 mm thickness to the surface of the treadmill.  They also measured the costs of running shod in lightweight shoes on the unpadded treadmill.  They found that when running barefoot, 10 mm of foam cushioning (approximately the thickness of the forefoot shoe midsole) afforded a benefit of 1.91%.   There was no significant difference between metabolic costs of shod and unshod running on the unpadded treadmill, indicating that the positive effect of shoe cushioning counteracts the negative effects of added mass.

Thus, running barefoot offers no metabolic advantage over running in lightweight, cushioned shoes. The explanation for this remains speculative.  One possible explanation is that when running barefoot, a runner maintains a lesser degree of stiffness in the legs, resulting in less efficient capture of impact energy as elastic energy, in the same manner as a floppy spring produced a less efficient recoil that a stiff spring.

While light weight shoes might offer adequate protection in short and medium distance events, it is necessary to consider the possibility that in a marathon or ultra-marathon, the cumulative damage from repeated eccentric contraction will result in a significant loss of power.  A little more padding might protect against this loss of power.    Similar issues apply during periods of high volume training.  Last summer, while training for a half-marathon, I built up my total training load to a substantially higher volume than during any recent year and found that I suffered a gradual accumulation of aches in my legs.  Hence, at least for an elderly person, light weight shoes should be employed sparingly, but nonetheless, frequently enough to produce the adaptive changes required if they are to be used for racing.

Conclusion

My overall conclusion is that for racing distance up to half a marathon, light weight shoes with near zero drop from heel to toe are preferable, as these give the optimum combination of efficiency and protection.  Unless the legs have been very well conditioned to the rigours of long races, for the marathon and ultra-marathons it might be preferable to use a little more padding.  Similarly, during periods of very high volume training, a modest amount of additional padding might provide helpful additional protection.  Motion control is only sensible if there is a clear need

The big debates of the past decade: 1) Running style

February 17, 2014

In those distant days when I was a fairly serious athlete, we did not think much about style.  Emil Zatopek’s three gold medals in Helsinki a few years previously had suggested that training mattered far more than style.   The ungainly tension in his neck and shoulders was an irrelevancy. We were much more interested in the word-of-mouth rumours of his prodigious training sessions.  At the time, we debated the merits of Percy Cerutty’s advocacy of running up sand-hills in contrast to Arthur Lydiard’s advocacy of 100+ miles per week.  Neither style nor injuries were a major preoccupation.

In contrast, during the past decade, running style has become a focus of attention among elite and recreational athletes.  The focus of the elites is illustrated by Alberto Salazar’s efforts to improve Mo Farah’s efficiency prior to his attempt at the London marathon this year. But perhaps even more importantly, style has been a focus of attention of recreational runners concerned about repeated injury.

A decade ago, distance running had blossomed into a mass participation sport and injuries were rife. Marketing of running shoes had become a major commercial enterprise.   The running world was primed to embrace the idea that running no longer came naturally to modern man.  Was it a consequence of wearing shoes all day or sitting for hours at a desk?  Maybe even it was the training shoes that large commercial companies encouraged us to buy.

The time was ripe for the emergence of gurus with messages about how to run naturally.  Techniques such as Pose and Chi became popular.  These techniques were embraced with almost religious fervour and many of the disciples found relief from their recurrent injuries.  Unfortunately other novices came away from their flirtation with these techniques with new injuries, especially problems with the Achilles tendon.  Now, a decade or so later, the reasons for these contrasting experiences are fairly easy to identify.   Although a few important issues about running style remain unresolved, the decade of experience and of research has provide fairly clear answers to the major questions.

Natural running: forefoot or heel strike?

One of the most hotly debated issues has been the question of heel striking versus fore foot striking.   In part, this debate arose from an idealistic quest to identify mankind’s natural running style, unsullied by the influence of modern life styles.  I will focus predominantly on Pose because its strengths and weaknesses are fairly well documented in books, research papers and on the Pose Tech website.  The second chapter of ‘Pose Method of Running’ (Pose Tech Corp, 2002) opens with an examination of images of runners on classical Greek pottery.  One of the images is from an amphora depicting runners at the panthenaic games in 530 BC.   The inventor of Pose, Nicholas Romanov writes:  ‘Look at these drawings and you will see quite clearly that all the athletes run on the front part of the foot without landing on the heel.  As barefoot runners this was the obvious technique for efficiency and to avoid injury.  To my mind this barefoot running style of landing on the forefoot is the purest example of the proper nature of running….As the Golden Age of Greece passed mankind appeared to leave these values far behind’.

Fig 1: Runners at the panathenaic games 530 BC .   These athletes were competitors in the stadion, a sprint over a single length of the track (over 200 meters).   Terracotta Panathenaic prize amphora, attributed to the Euphiletos Painter.  Copyright, The Metropolitan Museum of Art,  www.metmuseum.org

Fig 1: Runners at the panathenaic games 530 BC . These athletes were competitors in the stadion, a sprint over a single length of the track (over 200 meters). Terracotta Panathenaic prize amphora, attributed to the Euphiletos Painter. Copyright, The Metropolitan Museum of Art, http://www.metmuseum.org

The appeal to a golden age of classical Greece subsequently received some support from rigorous science.   Based on evidence that  our distant ancestors living on the African Savanah around 2 million years ago were probably persistence hunters who relied on the their capacity to chase their prey to exhaustion, Daniel Lieberman and colleagues at Harvard University examined the foot strike pattern of barefoot runners in comparison with runners wearing modern running shoes.  He found that barefoot runners tended to land on the forefoot or midfoot whereas runners wearing shoes tended to be heel strikers.  The heel strikers experienced a more rapid rise in the loading of the legs in early stance, although Lieberman was careful to avoid claiming at that stage that fore-foot striking would result in a lower injury rate.

Further investigation casts some doubt on the conclusion that habitual barefoot runners are not heel strikers.  A study of habitual barefoot runners from north Kenya by Hatala and colleagues did provide further evidence that forefoot strike reduces the magnitude of impact loading.  However, these habitually barefoot Kenyan runners tended to land on midfoot or forefoot only when running at sprinting speed, where impact loading is high.  The majority of them landed on the heel at endurance running speeds (5 m/sec or less).  At their preferred endurance speed (average of 3.3 m/sec) 72% were heel strikers.  Could it be that heel striking is actually more efficient at endurance paces?

Is heel striking more efficient at endurance paces?

Ogueta and colleagues from Spain compared efficiency in two well matched groups of sub-elite distance runners and found that heel strikers are more efficient than midfoot strikers, across a range of speeds.  Heel  strikers were 5.4%,, 9.3% and 5.0% more economical than mid-foot strikers at speeds of 11, 13 and 15 km/h respectively. The difference was statistically significant at 11 and 13 km/hr, but only showed a trend towards significance at 15 Km/hr.  DiMichele and Merni from Italy, who tested runners only at a single speed of 14 Km/hour, found no significant difference in efficiency between sub-elite heel strikers and mid foot strikers.  Overall, the evidence suggests that at paces typical of recreational endurance running, heel striking is more efficient but the advantage diminishes as pace increases.  This is consistent with the observation that in most runners the point of contact at footfall moves forward along the sole of the foot as speed increases.

These studies were cross sectional studies comparing different runners.   Indirect evidence of the effect of a change to forefoot landing within an individual is provided by the longitudinal study by Dallam and colleagues of 8 athletes who changed to Pose.  They found that 12 weeks after changing to Pose, the athletes were on average of 7.6 percent less efficient than before the change.    Perhaps 12 weeks is not long enough to achieve facility with a new style, but the consistency of the magnitude of the penalty associated with forefoot/midfoot striking in the study by Ogueta and the penalty attributable to Pose in the study by Dallam adds weight to the conclusion that heel-striking is more efficient at endurance paces.

With regard to risk of injury, the evidence is more complex.  In a retrospective study of US collegiate distance runners, Daoud and colleagues found that habitually rear-foot strike had approximately twice the rate of repetitive stress injuries than individuals who habitually landed on the forefoot. Traumatic injury rates were not significantly different between the two groups.    The sharp initial rise of ground reaction force observed with heel strikers is a likely factor in the risk of injures such as tibial stress fracture.  It is noteworthy that during  a session that included a total of approximately an hour of running at lactate threshold pace, Clansey and colleagues found that several kinematic variables, including rate of rise of ground reaction force in early stance, increased significantly, suggesting an increased risk of stress fracture with increasing fatigue.

However, mid-foot and forefoot strike have their own risks, especially for the muscles and connective tissues acting at the ankle, as indicated by the Capetown study of Pose.  Consistent with this, Almonroaeder and colleagues found a 15% greater load (averaged over stance) and an 11% greater rate of rise of tension in the Achilles tendon in mid-foot and forefoot strikers compared with heel-strikers.

Should the push be conscious?

One of the features that appears to account for some of the success of Pose in reducing injury rates among its dedicated disciples is the avoidance of a conscious push against the ground.   In reality, force plate data clearly demonstrates that runners do push against the ground, with peak vertical forces often exceeding three times body weight.  A study by Weyand and colleagues demonstrates that faster runners push harder against the ground.   Many elite sprinters, including Usain Bolt, report that they do consciously push.   However, my own speculation is that for recreational distance runners, a conscious push can be harmful if it encourages a delay on stance, and an associated increase in braking.  Paradoxically, since the delay decreases airborne time, a lesser vertical push is required to maintain the airborne phase, but a greater horizontal push is required to overcome braking.   Excessive horizontal push is potentially harmful, as we will discuss in the section on risks of braking, below.

Perhaps serendipitously, Pose discourages this potentially harmful conscious push by investing faith in the illusion of gravitational free energy.  According to Nicholas Romanov, one of the most important principles of Pose is the ‘Do Nothing Concept’ which he describes on pages 88 and  89 of Pose Method of Running:   ‘We must learn to get out of the way and let gravity propel us forward while we preserve as much of our energy as possible by the simple act of picking our feet off the ground.’

In the words of Romanov and Fletcher: ‘Runners do not push off the ground but fall forwards via a gravitational torque’.  Pose theory draws on the observation that pivoting forwards is an effective way to initiate the action of running to explain how gravitational free energy can allegedly be harnessed even during running at a steady speed. The theory proposes that this can be achieved by employing the sequence of Pose, Fall, Pull, in the period from mid-stance to lift-off.  Romanov’s description of the Pose does in fact match the balance posture of many good runners at mid-stance: knees and hips are slightly flexed while the hips and shoulders are aligned over the point of support through which force is transmitted from foot to ground.  However, the Fall, which Romanov claims provides gravitational free energy, simply does not occur.

The body’s mass rises rather than falls in the second half of stance. This is clearly predicted by computation based on the time course of ground reaction forces, and also clearly apparent from video clips.  The Pose Tech website claims that Usain Bolt employs Pose style, yet examination of the stills from the video of Bolt winning the 100m World Championship in Berlin in 2009 depicted on the PoseTech site, indicates that his hips and torso  rise about 7 cm between mid-stance and lift-off.   The origin of Romanov’s erroneous concept of the fall is revealed in fig 7 from his paper published with Graham Fletcher in Sports Biomechanics in 2007.  In that figure, the authors mistakenly assume that the vertical component of ground reaction force is equal to body weight whereas force plate data show that is several times body weight at mid-stance. I discussed this issue in greater detail in my post of  14 Feb 2010.   And finally, it no is more possible to get airborne by pulling the foot towards the hips than it is to self-elevate by pulling on one’s boot straps.

However, despite being based on fallacious theory, Pose does offer some benefits to at least some recreational runners.  The discouragement of harmful excessive  conscious pushing is balanced by focus on drills such as Change of Stance that help develop the neuromuscular coordination required to get off stance quickly.   However, a greater vertical push would be required to maintain the longer airborne time if stance time were to be decreased at constant cadence.  Pose technique averts this problem by encouraging increased cadence.   For recreational runners who tend to spend too long on stance and to run with cadence that is too low, Pose can be helpful.   However, short stance and high cadence each create their own problems.   A rational approach to the challenge of identifying the optimum foot-strike , duration of stance and cadence for an individual runner under particular circumstances requires an understanding of the benefits and risk associated with the three major  energy costs of running: overcoming braking while on stance; getting airborne; and repositioning the swinging leg during the airborne phase.

Balancing the three main costs

It is clear that efficient running requires a trade-off between the three major energy costs of running: getting airborne, overcoming braking and repositioning the limbs.  We can minimise the energy cost of braking by getting off stance quickly, but that creates a demand for greater energy expenditure to maintain a longer airborne phase, unless cadence is increased.  However, as described in my post of April 2012, increased cadence demands more energy expenditure to reposition the swinging leg, so we need to find a compromise that minimses total cost.  The optimum balance between the three costs  depends on pace and other circumstances, such as level of fatigue.   We also need to take account of the need to minimise injury.

Risks of getting airborne

Getting airborne demands a strong push against the ground.  It appears at first sight plausible that the stronger the push the greater the risk of injury. Surprisingly, studies that compare injury rates between individuals who differ in the magnitude of the vertical push they exert against the ground do not consistently find a significant association with injury rate.  This might well be because the strength that allows faster runners to push more strongly also helps protect them against injury.  Thus comparison between different runners might obscure a relationship between intensity of push and injury risk for an individual.

Some studies, reviewed by Zadpoor, do demonstrate an association between rate of rise of the vertical forces and risk of injures such as tibial stress fracture.  Rate of rise of force is related to both duration over which the force rises to a peak (determined largely by the type of foot-strike, with heel striking creating a steeper rise), and also by the magnitude of the average force (which is inversely proportional to the fraction of the gait cycle spent on stance).  Thus it is likely that at high speeds a strong push combined with mid or forefoot landing produces optimum efficiency and safety, though forefoot landing is only safe if the Achilles is well enough conditioned to take the strain.  For most runners it is probably safer to ensure that at least some of the load is taken on the heel in longer races.  At slower speeds, efficiency is greater with heel striking, and the risk of injury depends on whether the individual is more prone to adverse effects of stress at the knee or the ankle.  Stress on the knee is greater with heel-strike, but greater at the ankle with forefoot strike, as demonstrated in the Capetown study of Pose.

It should also be noted that precise timing of the vertical push is crucial.  For many runners, attempting to control the push consciously is counter-productive.   In contrast, most of us are capable of much more precise timing of hand movements.  Arm and leg on the opposite side are linked in their representation in the brain, and also, more tangibly, by the latissimus dorsi muscle and lumbar-sacral fascia that link the upper arm to the pelvis on the opposite side.  Therefore, conscious focus on a sharp down and backward movement of the arm can help ensure precise timing of the push by the opposite leg.  This sharp downswing of the arm should be accompanied by conscious relaxation of the shoulders.   I personally find this strategy more helpful than the cultivating an illusion of falling after mid-stance

Risks of braking

Braking generates both compression forces and shear forces at joints, and also increases stress on hip extensors which must overcome the excessive hip flexion associated with the forward angle of the leg at foot-strike.   One possible consequence is pain at the point of attachment of the hamstrings to the pelvis.   Therefore from the injury perspective excessive braking must be avoided but it is necessary to bear in mind that there is a trade off between the low braking costs of short time on stance and the costs of being airborne for a greater propotion of the gait cycle.  If excessive braking is to be avoided, it is crucial to avoid reaching forwards with the swinging leg, and ensure that the foot lands only a short distance in front of the centre of mass.  The jarring associated with braking can be reduced by ensuring that the knee is flexed slightly more than the hip at foot-strike, but the penalty is a loss of rigidity of the leg which might reduce the efficiency of the capture of elastic energy.  As discussed above there is a trade-off between braking and getting airborne.  Excessive braking demands excessive horizontal push after mid-stance, and an inevitable increase in total stance time.  For a runner prone to spend too long on stance focus on a precise push off, governed by conscious down-swing of the opposite arm can promote a good balance between the cost of braking and the costs of getting airborne.

Repositioning cost and cadence

The third element, leg repositioning cost, increases with increasing cadence, but conversely, the energy cost of getting airborne decreases with increasing cadence.  The  stresses on the tissues of the body associated with getting airborne, and therefore, the likely risk of injury, decrease with increasing cadence.    Therefore, many runners, both recreational runners and even some elites, including Mo Farah, might benefit from increasing their cadence, but not so far that the increased energy cost of repositioning become excessive.  The optimum cadence depends on various circumstances.  Based on observation of elite runners and the calculations presented in my blog posts in Feb and March 2012 suggest that optimum cadence is at least 180 steps/min at  4 m/sec, and  200 steps/min at 5.5 m/sec.   However the precise optimum for each individual will depend on leg strength and elasticity.  For runners with lesser power  and elasticity it is probably best to employ higher cadence, thereby reducing the need for vertical push.   As my leg muscle power and elasticity have deteriorated with age, I have been forced to increase cadence.  Typically my cadence is around 200 even at a pace of 4 m/sec.  This involuntary increase in cadence has helped minimise the risk of damage to my elderly legs, at the price of inefficient expenditure of energy on repositioning my swinging leg.  I am therefore working on increasing power and elasticity so that I can push off more powerfully and thereby decrease cadence safely.

Conclusion

Perhaps the most serious error promulgated by gurus is the claim that there is a single best style that is most efficient and safest.  The evidence regarding the greater efficiency of heel-striking at endurance paces, yet greater risk of at least some repetitive strain injuries with heel strike illustrates the fallacy of this claim.  The most efficient foot strike pattern, time on stance and cadence vary with pace, and in addition, the risk of injury depends on factors that vary between individuals, such as strength of muscles, tendons, ligament and bones.  Perhaps the most important strategy of all for minimising injury is building-up of training load slowly over time, and being aware of the effects of fatigue on form during demanding sessions.

Running style does play a crucial role but a much more nuanced approach based on an understanding of the costs and benefits of each aspect of form must be taken to identify what is best for each individual in their current circumstances.   The debate and the scientific studies of the past decade have indeed provided us with much information to make these nuanced judgments.

The five big debates of the past 10 years

February 6, 2014

The past decade has seen a continued growth of distance running as a mass participation sport.   The major city marathons continue to attract many thousands of entrants with aspirations ranging from sub 2:30 to simply completing the distance in whatever time it takes.  Perhaps more dramatically, parkrun has grown from a local weekly gathering of a few club runners in south-west London to an event that attracts many tens of thousands of individuals at hundreds of local parks, not only in the UK but world-wide, on Saturday mornings to run 5Km in times ranging from 15 min to 45 min before getting on with their usual weekend activities. Over this same period, the ubiquity of internet communication has allowed the exchange of ideas about running in a manner unimaginable in the days when distance running was a minority sport pursued by small numbers of wiry, tough-minded individuals whose main access to training lore was word- of-mouth communication.

Not surprisingly, within this hugely expanded and diverse but inter-connected community there have been lively debates about many aspects of running, with diverse gurus proposing answers to the challenges of avoiding injury and getting fit enough to achieve one’s goals.   Pendulums have swung wildly between extremes.  My impression is that the fire in most of the debates has lost much of its heat as the claims of gurus have been scrutinised in the light of evidence.   However, definitive answers have remained elusive.   What have we learned that us useful from this turbulent ten years?

There have been 5 major topics of debate:

1) Does running style matter and if so, is there a style that minimises risk of injury while maximising efficiency?

2) Are minimalist running shoes preferable to the heavily engineered shoes promoted by the major companies?

3) What is the optimal balance between high volume and high intensity training in producing fitness for distance running?

4) Is a paleo-diet preferable to a high carbohydrate diet?

5) Does a large amount of distance running actually damage health, and in particular, does it increase the risk of heart disease.

In all five topics, debate still simmers.  I have scrutinised the scientific evidence related to all five of these question in my blog over the past seven years, and I hope I will still be examining interesting fresh evidence for many years to come.   However whatever answers might emerge from future science, in our quest to determine the answers that will help us reach out running goals we are each an experiment of one and now is the point in time when we must act. I think that the evidence that has emerged in the past decade has allowed me to make better-informed choices in all five of these areas of debate than would have been possible ten years ago.   In my next few posts, I will summarise what I consider to be the clear conclusions for the past decade of debate, what issue remain uncertain, and what decisions I have made with regard to my own training and racing.

For me personally, the greatest challenge as I approach my eighth decade is minimising the rate of inexorable deterioration of muscle power, cardiac output and neuro-muscular coordination that age brings.  Therefore my approach to these debates is coloured by the added complications of aging.  Nonetheless, my goal is not only to continue to run for as many  years as possible, but also to perform at the highest level my aging body will allow during these years.  I hope that the conclusions I have reached will be of interest to any runner aiming in to achieve their best possible performance, whatever their age.

Gazelles v gliders: Mirinda Carfrae v Chrissie Wellington

April 30, 2013

As described in a recent post, my attempt to recover some of the speed of my youth by engaging in a lifting program to re-build my leg strength was only partially successful.  I exceeded my expectations regarding gains in strength, but so far this has not been translated into increased speed.  Unfortunately a recurrence of arthritis has confounded my immediate hopes, and at the moment I am more concerned about re-building my aerobic base.  However a recent discussion of the merits of gazelles v gliders on the Fetch efficient running thread has prompted me to re-examine the issue of my loss of speed.

The most striking thing about the change in my running style as I have grown older is the fact that my stride length has shortened.  Now, whenever I try to increase pace, my cadence automatically increases, often going well above 200 steps per minute even at a modest pace. While many recreational runners might benefit from an increase in cadence, at least up to 180-190 steps/min, I am fairly sure that in my case, the increase in cadence reflects reduced ability to get airborne, leading to a stunted stride.  I had attributed this to lack of strength but maybe strength wasn’t the main problem.

The gazelles v striders comparison provides food for thought.  Here is a good illustration (though I do not agree with all of the comments by the commentator).   The crucial difference between gazelles and gliders is that gliders do not produce as much elevation of the body on each step as gazelles. Because they produce less elevation than gazelles, their stride is shorter and they employ a higher cadence.  While I am not sure that even my mother would have ever described me as a gazelle, there is little doubt that I have become a glider as I have aged.   This is what I have been trying to correct.  However, this video clip provides at least some grounds for questioning the need to overcome my tendency to be a glider.   As the video illustrates, Chrissie Wellington, without doubt the greatest female triathlete ever, is a glider.    In the video, Chrissie’s gliding is compared with the style of one of the most elegant triathlete gazelles, Mirinda Carfrae.

The costs of gliding

Could it be that gliding is efficient?  It is tempting to think that reducing elevation costs must be more efficient, but this would be far too simplistic.  When considering efficiency, we need to consider the three major energy costs of running:

1)            Overcoming braking.  Provided a glider increases cadence to ensure that time on the ground does not increase, the braking cost per step will be the same for both but the cost per  mile will be  greater for the glider because there are more steps per mile.

2)            Limb repositioning costs: these increase with cadence and will be higher for the glider

3)            Elevation costs:  Although the video commentary  incorrectly states there are no elevation costs, in fact elevation of the centre of mass occurs before lift- off as a result of extension of hip, knee and ankle during the late stage of stance.   Furthermore due to the higher cadence, the saving in elevation cost per step is partially offset by the greater number of steps per mile.  However, the elevation cost per mile will nonetheless be somewhat lower for a glider because elevation cost increases as the square of airborne time, so the saving in elevation cost per step is relatively greater than the extra cost due to more steps per mile.

In estimating the total cost, we need to balance the three variables: braking and limb repositioning costs are greater for the glider, but elevation costs are less.  At higher speeds, repositioning costs become the dominant cost and there is no doubt that at high speed (e.g. faster than 7 min/mile) gazelles are more efficient.  At intermediate speeds (7min/mile-10 min/mile) braking costs and elevation costs are both quite appreciable and at such paces too, gazelles are almost certainly more efficient.  At very low speeds (slower than 10 min/mile) braking cost become relatively small because the leg is never far from vertical and therefore the horizontal ground reaction force that produces braking is always low.  At such paces the major goal should be minimising elevation costs.  So on balance, I think it is only at very slow paces that gliders might be more efficient than gazelles.

So why is Chrissie Wellington a glider?   I do not know, but wonder whether it might be an unconscious attempt to decrease the risk of injury when tired in the late stage of an ironman.  With regard to injury, the issue is the relative risk of a larger number of smaller impacts for the glider compared with fewer larger impacts for the gazelle.  While the phenomenon of repetitive strain injury demonstrates that repeated small impacts can be damaging, I suspect that size of the impacts plays an even bigger role in damage.  Therefore, I am inclined to think that for a tired runner, (either in the late stages of an ultra or an ironman) the risks will be lower for the glider.

Overall, there is little doubt that the gazelle style is better for medium paced and faster running, but there is reason to debate whether or not the glider style might be beneficial for tired, slow runners. I am still eager to become as much like a  gazelle as my aging limbs will allow.  While I can no longer blame lack of strength, I wonder if maybe lesser ability to capture elastic energy at foot fall is the cause of my gliding.   In a future post I will describe my plans for the attempt to recover elasticity.   But in the short term, my focus is on re-building my aerobic base, and that is what my next post will address.

Finally, it is noteworthy that on the two occasions when Chrissie Wellington and Mirinda Carfrae went head-to-head in the world ironman championship (at Kona in 2009 and 2011), on each occasion Wellington won the overall event but on both occasions Carfrae ran the faster marathon. In my opinion Wellington is the greatest female triathlete ever but Carfrae is the more efficient, and faster, marathon runner.

Added note (4th May 2013)

In his comments below, Robert had pointed out that I have not provided adequate justification for my claims about the energy costs.   My claims are based largely on calculations based on applying Newton’s equations of motion to the simplified model of running described in my posts in January and February 2012.    At a pace of 4 m/sec, (which is close to that of Carfrae and Wellington in the world ironman championship in 2011) the calculations demonstrate that the combined cost of elevation and braking is 6% greater for a Glider than for a Gazelle, assuming that that the Glider has an increased cadence sufficient to produce a similar time on stance.  Observations suggest that Gliders do increase cadence to maintain a similar time on stance, and furthermore, if a Glider did not have increased cadence they would be even less efficient because the longer time on stance would produce an even greater increase in braking costs (as indicated by my post of February 2012).

The crucial questions is whether or not the simplifications I used in performing these calculations lead to serious errors. There are two respects in which the simplifications might lead to error.  First, I assumed a sinusoidal shape for the variation of ground reaction force with time.   Variations in the shape of this curve introduce small changes to the results of the calculations, but in the absence of force plate data for each runner, I cannot do a more precise calculation.  However, the error due to this simplification is likely to be small.

The other potential source of error is that my calculations are for the total energy expended on elevation and overcoming braking. I have not subtracted the energy saving expected via elastic recoil.  If a runner maintains greater tension in the leg muscles, as recommended in the BK running style, it is possible to recover a greater proportion of the required energy via elastic recoil.  I cannot exclude the possibility that a Glider might maintain greater tension in the leg muscles, but think that in general this is unlikely as increased tension in the leg muscles results in a greater rate of rise in ground reaction forces and potentially increases the risk of injury.  The advocates of the BK style recommend thorough preparation using plyometrics before attempting this.  I think that increasing leg muscle tension would not be a good strategy for a tired ultra runner.  Thus I doubt that Gliders make greater savings via elastic recoil than Gazelles. I suspect that the opposite might be the case, though this is speculation.  However even if equal efficiency of recovery of energy via elastic recoil is assumed, the Glider incurs a 6% greater cost for elevation and braking than the Gazelle.

Also, it should be noted that my calculations do not include limb repositioning costs. These costs are almost certainly higher for the Glider because repositioning cost increases with cadence (as discussed in my post in April 2012) and furthermore, the trajectory of the foot of a Gazelle results in a shorter lever arm of the swinging leg, further increasing efficiency.

On balance, I think it is likely that my calculations provide a fairly realistic estimate of the relative costs of elevation and braking for the two styles.

Mary Keitany, a muscle named Lady Dorothy, and the future of the women’s marathon

June 3, 2012

The past decade has seen an astounding increase in the standard of marathon running, at least in the men’s event.  Not only has the world record continued to tumble but the event has become a race from start to finish.  This was clearly evident in Wanjiru’s victory in Beijing, but was also made manifest in the London marathon a few weeks ago by Wilson Kipsang’s devastating surge beginning as he approached Tower Bridge, around the half-way mark, and continuing for more than 5 Km at 2:50 per Km (sub 2 hour marathon pace).  Abel Kirui hung on until 35 Km but the damage inflicted by Kipsang’s self-assured mid-race surge became apparent as Kirui’s pace slowed to about 4 min/Km and he dropped back from 2nd to 6th place over the final few Km.  Just as significant as the shift towards the mental toughness exemplified by Wanjiru in Beijing and Kipsang in London, is the manner in which the winner in most male events nowadays maintains a graceful but powerfully efficient stride similar to that we are used to seeing in a track 10,000m, all the way to the finish.   The era in which gruelling training and gritty determination took Emil Zatopek to victory in 5000m, 10000m and marathon in Helsinki is a distant memory.  The marathon is no longer merely a test of endurance, but an event that calls for tactical finesse coupled with the ability to sustain a powerful efficient gait for 42.2 Km.

How does the women’s marathon compare?  

In contrast, advance in the women’s event has been much more patchy.  Although Paula Radcliffe’s record of 2:15:25 set in London in 2003 with the assistance of two male pacers is widely regarded as phenomenal, it is not clear that it is especially outstanding when compared with the men’s record.  One might expect that in the marathon that efficiency should count for more than strength, and that women would be less disadvantaged relative to men, than in shorter events.  The evidence is ambiguous.  Across the range of distances from 100m to marathon, the female world record is slower than the male record by a margin of 9-12%.  FloJo’s time for 100m is 9.5% slower than Usain Bolt’s, though controversy lingers over FloJo’s performance.  Similarly, a cloud unfortunately hangs over Marita Koch’s 400m time, which is 10% slower than Michael Johnson’s.  Paula’s marathon record is 9.5% slower than Patrick Makau’s record of 2:03:38.  Furthermore, whereas no other woman has approached Paula’s time, at least 3 other men have demonstrated the potential to demolish Makau’s record.  Kipsang missed that mark by only a few seconds in Frankfurt last year, while both Geoffrey Mutai (2:03:02) and Moses Mosop (2:03:06) have actually recorded times faster than Makau’s record on the demanding down-hill Boston course, which unfortunately does not satisfy world record requirements.  Unlike the performances of Flo-Jo and Marita Koch, no clouds hang over Paula’s performance in London in 2003, and it is truly an outstanding performance.  But if we acknowledge that strength is less of an issue in the marathon compared with sprints, it is not clear that Paula’s female marathon record is any faster than might reasonably be expected.

More grit than grace 

When it comes to style, Paula’s head bobbing is legendary.  But it is not merely a matter of head bobbing.  She carries her shoulders high and her torso lurches.  Her victory in Chicago in 2002 when she broke Katherine Ndereba’s world record, was a triumph of gritty determination, but it was as painful as it was awe- inspiring to watch her straining virtually every muscle in the final few Km.  In London, 8 months later, as she turned into the Mall on her way to smashing her own world record, the strain in her upper body was only slightly less apparent.  Perhaps Paula Radcliffe is the Emil Zatopek of the woman’s marathon.  Katherine Ndereba is markedly different.  She is always graceful.  To my eye she swings her arm too far back and leaves her trailing foot on the ground for a little too long, resulting is a slightly delayed swing.  However the issue of how quickly the trailing foot should lift-off stance remains a controversial topic which I will return to again in a future post.    While there can be no denying that Ndereba is graceful, I think her race tactics have cost her dearly on a number of occasions, most notably in Beijing in 2008.  On previous occasions she had been prepared to let the leaders get ahead by a minute or two, only to subsequently nibble away the margin and take command in the final few Km.  In Beijing she allowed Constantina Tomescu-Dita to get away, and then she could not catch her.

Tomescu-Dita entered the stadium with arms flailing in a manner that could scarcely be described as graceful, though it was heart-warming to see a 38 year old achieve such a spirited Olympic victory.  Ndereba and Zhou entered the stadium several minutes later, and when Zhou challenged for the silver medal with less than 100 metres to go, Ndereba sprinted away elegantly.  Whether or not a more spirited performance at an earlier stage would have given her Olympic gold is unknowable.   She has indeed many memorable marathon honours to her credit, including gold medals in the world championships in the pre-Olympic years, 2003 and 2007, but on each occasion she achieved only silver in the Olympics the following year.  In their different ways the two women who dominated the marathon in the past decade might look back ruefully on the Olympics of 2004 and 2008.   Paula still has a slender chance in 2012 following a creditable 2:23:46  in Berlin last year, but Katherine now hands over the mantle of Kenya’s queen of the marathon to be shared by a handful of promising younger women, including this year’s London winner, Mary Keitany.  Might this new generation of Kenyan women do for the women’s marathon what their male compatriots have done or the men’s event?

A new era?

In contrast to the men’s event in London in April 2012, the elite women started cautiously, reaching the halfway mark in 70:53, but shortly after a new pattern emerged. It was not the male-type self-assurance of Kipsang, but rather a quiet, unassuming yet determined increase in pressure by  Keitany.  Her pace for that middle 5Km provided only a hint of her gathering speed, but she continued to accelerate, covering the 5 Km from 35 to 40km in 15:45.  Ross Tucker in Science of Sport reports that this is the fastest 5Km split ever recorded by a woman in a major marathon, faster even than Radcliffe’s 15:47 for the first 5Km in London in 2005.   In the final 2Km Keitany increased her pace even further to a pace only slightly slower than 3 min/Km.

I believe that a major factor that transformed Radcliffe from fourth placed 10,000m runner in Sydney in 2000, to a sub-2:16 marathoner in 2003 was an increase in her leg strength resulting from a program of plyometrics introduced by Gerry Hartman after the Sydney Olympics.  Maybe Paula’s 2:15:25 will only be seriously challenged when women marathoners develop the type of strength that took middle distance runner Kelly Holmes to a gold medal double in Athens, but I am inclined to think that for a marathoner efficient muscle recruitment is even more important than sheer strength.  Observing the video of Mary Keitany in VLM 2012 suggests that her efficient gait was a major factor in her ability to increase speed steadily despite accumulating exhaustion in the late stages.

Controlling rotation of the torso

Keitany swings her arms in a neatly controlled manner that sets the tone for her trunk and legs. As her arm swings down and back close to her body, the hip of her swinging leg rotates forward and the contralateral hip rotates back.  By virtue of allowing her pelvis to rotate she minimises wasteful angular rotation of the whole body around the vertical axis.  In general, her foot usually lands fairly near the midline of the body when viewed from the front (eg at 1:55:13).  In contrast, Edna Kiplagat, who vied with Keitany for the lead until around 35 Km, and Priscah Jeptoo, who eventually finished in third place to put three Kenyan women on the podium, both land more often with the foot more to the side of midline, due to lack of rotation of the pelvis. If the foot is grounded to the side of the midline, the body must rotate around the vertical axis, on account of the momentum of the torso.  The tendency for the torso to swing around can be minimised by a counter rotation of the arm.  Because a less compact body has a greater moment of inertia, if the arm displaced outwards, the angular displacement of the torso itself is reduced but the angular momentum of the torso plus arms is not.  This angular momentum must be cancelled in the next step, which wastes energy.

Lady Dorothy

The crucial link that coordinates the action of arm and opposite leg is provided not only by the motor programmes the evolved in the brains of our distant quadripedal ancestors, but also by a direct connection via the most extensive muscle of the human body: Latissimus dorsi.  The Latin name means ‘widest back muscle’.  Body builders refers to this muscle when they talk about  developing their ‘lats’, while medical students call it ‘Lady Dorothy’ to help them remember the arrangement of its attachment to the humerus in the upper arm.   The mildly bawdy mnemonic  ‘Lady Dorothy lies in a ditch between two majors’ reminds them that its tendon runs in a groove between the attachments of Pec Major and Teres Major.   However this mnemonic serves to reinforce the role of Latissimus dorsi in pulling the arm inwards and back, while distracting attention from its attachment to the thoraco-lumbar fascia (TLF).

Figure 1: Latissimus dorsi (in red) and its attachment to the iliac crest and lumbar spine via the thoraco lumber fascia (From Grays Anantomy)

When the left foot is grounded and the hip extends back, the glutes on the left side stabilise the pelvis, providing a firm anchor point for the TLF along its line of attachment to the iliac crest.  The simultaneous contraction of latissimus on the right side, pulls the arm back while rotating the lumbar spine so that the left side of the pelvis rotates forwards while the more lateral, vertically oriented muscle fibres tend to prevent it dropping as the swing leg moves forwards.  Thus the coordinated action of glutes with the latissimus stabilises the pelvis in a horizontal position as seen from the front, while allowing it to rotate about the vertical axis that facilitates the efficient passage of the swinging leg.

Figure 2: Posterior hip muscles (from Wikipedia) When the left foot is on stance, G. maximus on the left anchors the left side of the pelvis, thereby proving a firm anchor via the thoraco-lumbar facscia for right sided Latissimus dorsi as it contracts to pull the right arm down and back. Simultaneously G. medius (on the left) minimises the downwards tilt of the pelvis from left to right.

Avoiding snagging of the ITB

However this action must be quite precisely controlled.   If the swing leg rotates too far, carrying the foot too far towards the midline at foot-fall, the ilio-tibial band (ITB), which is under tension as it provides the anchor for gluteus maximus, will be dragged across the bony protrusion of bone on the lower end of the femur.  This problem will be greatly exacerbated if the pelvis has been allowed to tilt down on the side of the swinging leg.  This makes the angle between pelvis and femur even more acute, dragging the ITB closer to the femur.  This problem will also be exacerbated if the foot is prevented from pronating as the stance leg tends to twist over the grounded foot.   Thus, if risk of injury is to be minimised there is quite limited tolerance in the allowed range of rotation of the pelvis and movement of the swinging foot towards midline.  Sideways drop of the pelvis must be limited and adequate pronation of the foot allowed.    It is likely to be counter-productive to focus consciously on controlling all of these movements while running.  I believe that conscious attention to a neatly controlled arm swing, in which the hand sweeps down close to the body from a point to the side of the midline and a little above mid-chest height, towards the hip, is the best way to trigger the non-conscious motor control program that coordinates all of this.  The extent of the swing should increase a little as speed increases, but the hand should never cross the midline.

The crucial role of a stable core

Precisely controlled rotation of the pelvis about the vertical axis and minimal tilt from side to side is crucial not only for maintaining an efficient gait for the duration of a marathon, but perhaps even more importantly, for avoiding injury during the high volume training that the marathon demands.   While I believe that the program of plyometrics which Gerald Hartman introduced in 2001 to develop leg strength played a key part in the transformation of Paula Radcliffe into the most outstanding female marathoner the world has yet seen, I suspect that greater attention to the coordination of the complex system of muscles extending from shoulder to foot via Latissimus dorsi, the glutes, ITB and the lower leg muscles, might have protected her from the injuries that confounded her Olympic dreams in 2004 and 2008.

 

The future of the women’s marathon

With her victory in London in a time of 2:18:37, Mary Keitany broke the Kenyan women’s marathon record established by Catherine Ndereba in the 2001 Chicago marathon.  Ndereba’s  time of 2:18:47 was not only the Kenyan record but also the world record in 2001.   However it is noteworthy that even a decade later, Keitany shaved only 10 seconds off that time to take the Kenyan record, whereas in Chicago in 2002, Paula Radcliffe had taken possession of the world record by slicing almost a minute and a half off Ndereba’s time.  Then, the following year in London, Radcliffe took a further minute and 53 seconds off her own record.   While Keitany’s run in London in March has made her the favourite for gold in London in August 2012, Radcliffe’s world record is not threatened.  Keitany is now 30 and slightly older than Radcliffe was when she reached her peak, so the likelihood that Keitany will ever challenge Radcliffe’s record is receding.

The fact that three Kenyan women were on the podium in the World Championship in 2011 and again London in March this year confirms that Kenyan women are beginning to emulate their male compatriots’ domination of the event.  It is wild speculation to try to identify who among the current leading Kenyan women might eventually challenge Radcliffe’s record.  Nonetheless, I think that Florence Kiplagat is the one to watch – though her marathon performances so far have been erratic.  She did not finish her debut in Boston last year, but then looked very powerful and well-coordinated as she picked up speed in the final Km on her way to winning the Berlin marathon 5 months later.  However, in London in April this year, her fourth place was not enough to secure her a place in the Kenyan 2012 Olympic team.  Perhaps the intense pressure that Kenyans, both women and men, faced to achieve Olympic selection this year had taken its toll.  But it is probable that at 25, Florence is still some way from her peak.  However, if the women’s marathon is the follow the path of the men’s event, the upcoming generation will need to combine the grit of Radcliffe with the grace of Ndereba and Keitany.

The Enigmatic Benefits of Pose

April 22, 2012

My post ‘Natural Running’ posted on March 29 has so far elicited 157 comments, which at first sight might indicate that it was a topic of wide popular appeal.  While I hope there is some truth in that, the number of comments actually reflects something different.  Of the almost 4000 apparently ‘serious’ views of my blog ( not including the almost countless number of spam hits) in the past three weeks, only 288 were views of that page.  Meanwhile, in the same three week period, my post from early March, ‘Does Usain Bolt run Pose Style,’ has been viewed over 500 times, while two of my perennially popular pages (‘Why do Marathon Runners have Skinny Legs?’ and  ‘HRV during Exercise’) have drawn a few hundred views each, as is typical of any three week period.   The popularity of the Bolt post is a pointer to the explanation for the large number of comments on the ‘Natural Running’ post. The majority of the 157 comments have been discussions between Jeremy, Hans, Simon and myself on issues closely related to Pose style.

I have enjoyed participating is this lengthy discussion especially because it has yet again emphasized several of the characteristic features of Pose.  One is the issue that drew Hans in to the discussion.  As I remarked in a recent post, Hans is a runner who previously suffered a number of injuries while running with an approach based on effortful pushing.  However, apart from some transient Achilles tendon problems, has enjoyed a relaxed, injury free running since taking up Pose, under the guidance of Jeremy.  Hans has been eager to understand the physics and biomechanics of running but has been left with a dilemma: how can he explain the clear success of his current relaxed Pose style of running in light of the apparent conflict with the principles of physics and biomechanics.  He has continued to design experiments to demonstrate that gravitational torque might provide kinetic energy which can be harnessed for propulsion when running.   We have discussed his proposed experiments in some detail in the comments section of ‘Natural Running’.  Hans has a clear enough understanding to see that ground reaction forces, both horizontal and vertical, must account for forward and upward motion of the body, but is still trying to devise the experiment that will demonstrate the role of gravitational torque, for the understandable reason that his experience demonstrates that Pose works.

Simon has occasionally chipped to the discussion between Hans and myself, sometimes to re-inforce to Hans the inevitable consequences of Newton’s laws of motion, and sometimes to remind me that even though Newton’s laws clearly demonstrate that a push against the ground is required, this is a push that is largely automatic, and to warn me that my use of the term ‘push’ creates danger of misdirecting recreational runners towards a running style that emphasizes conscious push against the ground.  In fact I agree strongly with Simon that for many runners it is counterproductive and perhaps even dangerous to produce a conscious push.  Meanwhile Jeremy, who was an elite athlete with a sub-4 minute mile to his credit in the days before he took up Pose, has contributed comments reflecting the more typical position of a Pose advocate: namely that experience demonstrates Pose is unarguably the right way to run and anyone who questions this is simply wrong.

As I have pointed out several times in the past, I have been  fascinated by Pose for almost eight years on account of the fact that  many recreational runners have found it has helped them run with fewer injuries, at least once that they have got beyond the Achilles problems that are common in the early stages.  As I and others have frequently pointed out, Pose is based on a faulty understanding of physics and biomechanics, so what is the secret to its success?

The most immediately apparent answer is that by creating an illusion that gravity provides free energy, Pose encourages the runner to stop consciously pushing against the ground.  Since we are far more likely to push as the wrong time or in the wrong direction if we try to impose conscious control on the organization of a process that is better left to the non-conscious motor control system in our brain, it is not surprising that Pose often works well, at least for recreational athletes.  However, if decreasing the rate of injury is merely a matter of disengaging our conscious mind from involvement in the task, simply chatting with a running partner should work just as well.  This is probably not the case, suggesting that there are some more positive reasons why Pose works.

While it would be fatuous for an outsider to claim to understand Pose with the insight of a disciple fully imbued with the tradition and rituals of the practice,  the long and challenging discussions with Hans and Jeremy left me with a feeling that I now understand what it is about Pose that works sufficiently well to allow me to fit these beneficial features into my own approach to running, without the need to embrace the cartoon physics.   So what are the elements of Pose that might be beneficial?

 

Acceleration

First, it is important to note the role of gravity is accelerating, either at the start of a run or when changing speed.  Leaning does allow us to use gravity to generate kinetic energy which can then be re-directed to provide horizontal acceleration by means of ground reaction force.  This involves a push against the ground but this push is mainly a reflex action to stop falling on one’s face.  So there is no doubt that gravity helps acceleration, even though the work is ultimately done by the muscles.  For a sprinter, he/she consciously pushes against the starting blocks and the ground but an endurance runner rarely perceives the push.

 

Minimising time on stance

When running at a steady speed, Newton’s first law, which states that a body continues in a state of uniform motion unless acted upon by a force, tells us that we can minimise the need for any push by minimising braking.  We minimise braking by spending a small time on stance.  There are two feature of Pose that minimise braking.  The first is high cadence.  This results in a shorter gait cycle, including shorter time on stance and shorter airborne time. The shorter airborne helps reduce stance time by virtue of the fact that the impulse required to get airborne can be delivered within a shorter stance time (for a specified value of average vertical Ground Reaction Force).

The other relevant feature of Pose that helps achieve a short time on stance is the mental focus on rapidly pulling the foot from the ground.  This pull is supposedly led by a hamstring contraction (see Pose tech article 000280). In fact it is an illusion that pulling gets us airborne. It is a push that gets us airborne, though a substantial portion of the energy for this push is provided via elastic recoil.  By encouraging a mental focus on pulling the foot from the ground, Pose encourages a short time on stance. I believe this is largely achieved by producing non-conscious pre-tensioning of the hip extensors (hamstrings and gluteus maximus) in late swing, leading to a strong contraction of these muscles at foot-fall, thereby capturing impact energy as elastic energy and contributing to the build up of a strong push against the ground.  This arrests the falling body and propels it forward and upwards after mid-stance.  However, Dr Romanov argues that the hamstring contraction at the end of stance provides an upwards pull that breaks contact between foot and ground.  While there is no doubt that the push (admittedly largely automatic and powered at least in part by elastic recoil) is what generates the ground reaction force that propels the body upwards, it is nonetheless feasible that by pulling the foot towards the upwardly moving hips, a hamstring contraction might contribute to breaking contact.  To understand the role of this hamstring contraction, it is necessary to consider what happens in early swing phase

 

The mechanism of the swing

The principle role of the swing is to get the foot forwards from a position behind the torso at the end of stance to a position a short distance in front of the torso at footfall.  In early swing phase, both hip and knee flex.  The flexion of the hip causes the thigh to move forward and up while and the knee flexion causes the foot to swing upwards relative to the thigh.   In Post Tech article 000280 Dr Romanov acknowledges that both the hamstrings and hip flexors play a role in this, but he strongly emphasises that the hamstrings play the leading role.  He argues that it is preferable to focus on a hamstring contraction rather than a powerful contraction of the hip flexors because not much work is required to achieve the swing.  In Chapter 8 of Pose Method of Triathlon Techniques, he states: ‘There is no need at all to move the swing leg forcefully forward; all the runner needs to do at this point is to continue to fall forward’

His justification for this claim is based on a seriously mistaken understanding of Coriolis force, but his claim does indeed contain a germ of truth.  Coriolis force is a virtual force that is invoked to account for the path of an object viewed by an observer in a rotating frame of reference.  Neither the runner nor a stationary observer is in a rotating frame of reference.  Coriolis force might only need to be invoked to account for the trajectory of a part of the body viewed via a video camera mounted on a rotating part of the leg or arm.   And even for such an observer, the Coriolis force would not be a real force; it would simply provide a way of describing the fact that the observed body part is moving relative to the observation platform.  By invoking Coriolis force as the force involved in the swing while pointing out that it is not a real force, Dr Romanov creates an illusion that very little work is required to swing the leg.  This is simply wrong.  In fact, at high speeds, the energy cost of swinging the leg  exceeds the costs of overcoming braking and of getting airborne (as discussed in my post of  April 5th, on cadence).

However, the germ of truth comes in the fact that in Chapter 8 of Pose Method of Triathlon Techniques, Dr Romanov explains how Coriolis force works by referring to the equation for the moment of inertia of a rotating body.  In the context of the swinging leg, this equation for moment of inertia has nothing to do with Coriolis force, but is very relevant to making the swing efficient.  The change in moment of inertia accounts for the remarkable effect obtained when the distribution of mass in a rotating objects is adjusted to make the rotating body more compact.  The effect is illustrated most dramatically by a pirouetting ice skater.  As the skater draws his or her arms in towards the torso the speed of rotation in increases. This is because for the amount of force that is required to produce rotational motion depends on both the mass of the object and the square of the distance of each part of the body from the axis about which it is rotating.   The moment of inertia of a body about a given axis is the sum of a contribution from each body part calculated by multiplying mass of the body part by square of distance of that part from the axis.   A smaller force is required to accelerate a compact rotating body on account of its relatively small moment of inertia.  If the body is already rotating, the law of conservation of angular momentum ensures that making it more compact will cause it to spin faster without requiring  input of more energy.

With regard to the swing leg, if the foot is folded up near to the buttocks as a result of knee flexion, it has a smaller moment of inertia and requires a smaller force (and less energy) to swing it.  Most coaches simply refer to this as the benefit of a short lever arm.

By spuriously invoking the concept of the virtual Coriolis force, Dr Romanov  has emphasised that it is best to avoid consciously driving the swing.  In fact, the pendular swing of the thigh around the hip and the lower leg around the knee does require exertion of force.  It is not purely driven by gravity. However much of the work of swinging the thigh is done by the psoas muscle which is buried deep in the pelvis.  Because it plays a major role in maintaining posture and in many everyday actions such a climbing stairs, psoas is a fairly strong muscle in most people.  Many runners are not aware of it, unless it is injured; and then they sometimes find themselves incapacitated for a period of months.  However most of the time psoas gets on with what we require of it without need for conscious attention.

Furthermore in late stance, the hip flexors, including psoas, are preloaded by the stretch that occurs as the torso moves ahead of the thigh, thereby extending the hip.  So at the beginning of the swing, psoas and the other hip flexors contract automatically.  If they did not, the leg and foot would drag behind the torso.   Although Dr Romanovs’ emphasis on the hamstrings as the prime mover in initiating the swing is based on erroneous physics and biomechanics, in practise it is probably best to avoid consciously driving the hip flexors.  Conscious driving is likely to lead to over-striding, in which the foot lands too far in front of the torso producing excessive braking, which wastes energy and might increase the risk of injury

 

Conclusions

Thus despite being based on erroneous physics and erroneous biomechanics, Pose does encourage the runner to engage muscles that achieve efficient running in an apparently less effortful manner, and to avoid conscious forceful contraction of muscles which are best left to contract automatically.  If we are to run well we need to avoid unnecessary or mistimed pushing.  In particular we need to avoid wasting kinetic energy by unnecessary braking and we need to learn how to capture impact energy via elastic recoil.    I therefore think that for recreational endurance runners Pose is better than a running style that is based on the mistaken belief that strong conscious pushing is required.   Elite sprinters do need to push consciously, but that is not our present topic.

However, while Pose has advantages for the recreational runner, there are two types of problem with Pose.  First, it creates the illusion that large forces are not required and this illusion does predispose to some injuries.  Secondly, for a recreational runner who wishes to achieve his/her best possible performance, there is a risk of failing do the type of training that is required.  To give one very specific example, the Change of Stance and High Knees drills involve similar movements: the flexion of hip and knee of one leg as it rises while the other leg descends to the ground.  However, CoS promotes precise timing while High Knees develops powerful hip flexors.  Pose places a disproportional emphasis on CoS at the expense of High Knees.   If we wish to achieve our peak performance we need to ensure that the hip flexors, including psoas, are powerful.

Summary

The emphasis on minimizing push against the ground avoids the dangers of a mistimed or delayed push.  In practice a push is essential to get airborne and to compensate for braking.  Nonetheless, by promoting high cadence and rapid lift-off from stance, Pose minimises the amount of braking while encouraging a non-conscious push.  Similarly, by minimising the role of the hip flexors during swing, Pose reduces the risk of harmful over-striding.  In practice, the required hip flexor contraction occurs automatically.  For the recreational runner for whom avoidance of injury is more important that achieving peak performance, Pose has several features to recommend it, including minimizing the risk of protracted push against the ground and the risk of over-striding.

Running naturally using sense and science

April 11, 2012

A few months ago I had a fairly clear idea about the content of my next few blog posts: my debate with Robert over the New Year period (recorded at length in the comments section of my Dance with the Devil article) had prompted me to tackle the issue of applying Newton’s equations of motion to running in a systematic manner, so my immediate priority at that time was a few technical articles on the mechanics of running.  After those articles, I intended to return to the issues of developing aerobic fitness; the influence of hormones such as growth hormone on tissue repair and regeneration; and some further accounts of my experiences with monitoring my heart rate.   This broad sketch is still on the drawing board but I have been waylaid by many interesting diversions. Apart from one post on the heart of the runner, that I felt could not wait too long because it was, in a way, my tribute to John Hadd, who had died while running a few months earlier, my posts this year have been heavily focussed on Newtonian mechanics, but many aspects of running mechanics remain untouched.

I anticipated that after the main article, posted on January 16th, in which I outlined the application of Newton’s equations to the motion of the runner’s centre of gravity (COG) and demonstrated the inevitable reality that getting airborne efficiently – the essence of efficient running – demands a short, sharp push against the ground, that I would easily tie up a few loose ends: important issues such a identifying optimum cadence and more peripheral issues such as dealing with wind resistance; but I had under-estimated the magnitude of the task.  In that first article, I had alluded in passing to the energy cost of repositioning the swing leg.  However I intended to by-pass this tricky topic by focussing on low to moderate speeds where repositioning costs are a minor fraction of the total energy cost.  However, Simon, whom I had come to know, at least in cyberspace, as a kindred spirit sharing a sceptical fascination with Pose technique, would not let me get away so easily with ignoring repositioning costs.  Others have jointed the debate from various perspectives, and as a result, I am still far short of my initial goal of reviewing the implications of Newton’s equations.  I continue to ponder the issues of aerobic fitness, tissue regeneration and heart rhythms, but my planned updates on these topics have been delayed.

The conundrum of the push

However, I have not been able to ignore another issue.  The conundrum that it is almost certain that for most runners, conscious focus on delivering a short, sharp push against the ground is not the best way to run safely and efficiently, except perhaps when sprinting.  It is this conundrum that has fuelled my long-standing fascination with Pose.  Despite the ‘looney-toon’ cartoon physics proposed by Dr Romanov in his book, ‘Pose Method of Running’, and unfortunately still lingering in articles on the Pose Tech website, there is little doubt that this irrationally-inspired running technique  has helped a large number of recreational runners to enjoy safer, more satisfying running.  There have also been many individuals disillusioned by being told by Pose coaches that their Achilles tendon injuries are simply due to not doing Pose properly, and others who have been disappointed that their race performances have not improved in the way they had hoped.  However, there does appear to be some magical injury-reducing ingredients in Pose.  One of these is the necessity to cut one’s training volume while developing the skill to perform the technique.  Furthermore, the reduced stress on the knee is an easily understood consequence of the Pose emphasis on forefoot or midfoot landing, though ironically it is the forefoot landing that puts the Achilles at risk.   The recommendation of high cadence reduces the magnitude of the force required for each step.  However, I think an even more important issue is the fact that the illusion that gravity provides ‘free energy’ allows Pose runners to achieve the essential short-sharp push against the ground without trying.

The secret

Is there a secret?  Many comments that have appeared on internet discussion threads in recent years imply that the secret lies in ignoring the physics; that  it is subjective experience that counts;   that we should perhaps revert to the noble primeval state of our Palaeolithic ancestors who are thought to have engaged in persistence hunting, barefoot, on the African savannah two million years ago.  The core idea is that thinking about what you are doing gets in the way of doing it.  In fact I strongly agree that attempting to exert conscious control over skills that our unconscious brain has learned to perform is often counter-productive.  However I do not believe that the secret is to revert to a primeval Palaeolithic state.  In fact I do not believe that would be natural.  In the two million or so years that separate early members of the Homo genus, such as Homo erectus who apparently had developed the musculo-skeletal features necessary for endurance running, from Homo sapiens with his/her large skull, we have developed an extraordinary capacity to achieve our goals, a capacity residing largely in our brains.

For several millennia, this capacity was strongly shaped by spirituality.  In the video recording of persistence hunting in our own era by bushmen in the Kalahari, narrated by David Attenborough, there is a moving moment near the end, after the quarry has been killed, in which the hunter strokes the head of the dead animal in acknowledgment of the spirit with which it had eluded its pursuer in an eight hour run across the savannah.   Spirituality is a key human persisting attribute.  If we are to be truly in tune with our own nature, we need to find a way to integrate the legacy we have received from our Palaeolithic ancestors with the capacity for science that is embodied in Newtonian mechanics.  For the present discussion, we can put aside relativity, quantum mechanics, and string theory.  Our Palaeolithic ancestors, perhaps unencumbered by too much weighty remembrance of the past or planning for the future, lived much more in the present moment, in which sensations not only of sight and sound, but also the sensations of the body in its environment, dominated awareness.  Can we run in a way that utilises both sense and science?

John Woodward, a practitioner of the Alexander Technique based in the Lake District where he teaches the art of running barefoot across the Lakeland fells, summarises the challenge: ‘.. in our modern lives our thinking caps (our heads) have become disengaged from our kinesthetic (body) sense. Unlike our ancient ancestor we are rarely in the vivifying moment but we languish in some past memory or crave some future state.’

Feldenkrais

I have been diverted into this train of thought by some challenging questions and comments on my article  on Natural Running (posted  on 29th March), especially by Hans, a Feldenkreis practitioner who had attempted various ways to escape his previous injury-prone running style before trying Pose, under the guidance of Jeremy Huffman.  Jeremy is an elite athlete with a sub-4 minute indoor mile to his credit, who has subsequently become a strong advocate of Pose, and frequently comments on this blog.  Jeremy helped Hans find the practical answer he was seeking, but left him with the challenge of understanding how Pose had worked while Feldenkrais had not.   Feldenkrais had been developed by Moshe Feldenkrais, who was an engineer who attempted to integrate a sound scientific understanding of human movement with a holistic awareness of one’s body in space.  Moshe Feldenkrias did not develop a theory of running but others, such as Feldenkrais practitioner, Jae Gruenke, have done so.  Hans concluded the emphasis on avoiding driving and pushing was a key issue in the success of Pose.  In his comments on my blog he initially questioned the necessity of the push.  After we had discussed a number of actual and hypothetical experiments that he devised, he was willing to accept that the push occurs, but proposed that the action of the leg might best be described and experienced as springy, rather than a push movement.  He agreed that that muscle work is involved in creating the springy effect, but this could happen without conscious effort

I agree that it is desirable to maximise the recovery of energy via elastic recoil, and certainly accept that it is best to let this occur with minimal conscious effort.   However, my own view is that we need a somewhat more comprehensive approach.  I think that it is best to cultivate a holistic perception of one’s body in space while applying a range of principles that are derived not only from physics and muscle physiology but also from neuroscience.

Some background

Perhaps it is time to give a little more detail about my background.  I began my scientific career as a physicist over forty years ago and subsequently have been fortunate enough to have had the opportunity do research in many different fields of science.  From physics I moved to biochemistry, or rather I integrated physics with biochemistry while holding joint academic posts in physics and biology.  Eventually, after several decades of diverse scientific and clinical experiences, I became what might be most accurately described as a neuroscientist, though I have always resisted labelling myself as a practitioner of a single discipline.  In the early 1990’s I was involved in some of the earliest investigations using modern brain imaging techniques to attempt to delineate the brain mechanism associated with willed action.  Since then I have continued to study brain function, mainly focussing on the conscious processing of information.  I am certainly not an expert in either the perceptual or motor systems in the brain.  Nonetheless, in some of my recent work using brain imaging techniques combined with electroencephalography (EEG), I have investigated the way in which the perception of bodily sensation engages the brain’s executive systems.

Although this work is exciting and high tech, it is also extremely primitive.   Indeed, while I am confident that neuroscience will furnish us with concepts that help us to understand many of the types of processes that go on in our minds and bodies, I believe it will never provide an understanding that matches the richness and diversity of personal experience.

In the days when I was doing my PhD in physics, I was also a marathon runner and a mountaineer.   Though physics, running, and spending time in the mountains were an integral part of my life, there were only a few strands that linked these activities.   Over the years, the rest of life’s activities displaced the running and, eventually, the adventurous aspects of mountaineering.  However nowadays I am once again running and also enjoying the hills and mountains, while I am still a scientist.  My forays into the intricacies of the human mind and brain have given me a slightly firmer foundation from which to try to integrate science, running and an appreciation of the natural world

The messages from neuroscience

Perhaps the most relevant message from cognitive neuroscience to the runner is that we can only focus consciously on a very small number of items of information at any one time, but the neural representation of many other aspects of a situation can be subliminally active in the background.  Furthermore, our brains are exquisitely sensitive to unexpected events. Thus we cannot focus on all of the aspects of running mechanics within a single gait cycle, but if we have practiced the actions and experienced the sensations often enough, the neural representation of most aspects of running are subliminally active, and are likely to enter into conscious awareness if the expected rhythm misses a beat.  In an attempt to instil the expectation of the pattern of activity involved in the swing of the leg from one stance to the next, I practice drills such as the Swing Drill.

The next important point emerges from our understanding of the sensori-motor systems: modern brain imaging has consolidated the observation of neurosurgeon Wilder Penfield at the Montreal Neurological Institute in the 1930’s, that the brain allocates far more of its processing resources to the hand than to the foot.   The region of the motor cortex devoted to the hand  is far greater in area than that devoted to the foot.  However, our brain can learn to integrate a complex set of muscle contraction into a single action.  Therefore, it is plausible that if we can link a set of movement of the hand to a set of movement of the leg and foot, we might be able to control this complex but integrated action more precisely.  Therefore I practice a version of the Change of Stance drill to establish in my brain a non-conscious motor program that combines a down sweep of my hand from a position near the sternum high on my chest wall towards my waist, with a quick extension of the flexed hip and knee of my elevated leg to the ground.  As I sweep my hand down, I hold forefinger and thumb lightly opposed to inculcate a sense of tidy but relaxed movement.  When I run, I rarely attend consciously to the extension of hip or knee but focus mainly on this brisk but relaxed and economical down-sweep of the hand.

This was the final sprint in a half-marathon a few years ago. I am 4449. The strain of running with a torn hip adductor, wrenched during a clumsy turn near the halfway mark, shows in the tense muscles in my neck and left shoulder, but the right hand, with forefinger and thumb lightly opposed at my waist is fairly well coordinated with the (non-conscious) push of my left leg.

The next important point to learn from the way in which our brain develops from infancy to adulthood, is that we learn how to detach unnecessary movement from a motor act.  A young child, when trying to do some intricate task with one hand, often exhibits mirror movements with the other.  Although we usually avoid this in adulthood, at times of stress, we are prone to introduce unnecessary movements.  Perhaps Paula Radcliffe’s tortuous movements of the neck during her 10,000m races in the late 1990’s were an illustration of this.  You can also see it in the picture of me.  However we have the capacity to release tension in unneeded muscles.    When I run I cultivate an awareness of the tension in my shoulder muscles, aiming for a sensation of the trapezius muscle relaxing to allowing my shoulders to relax downwards and slightly back.

I also find it helpful to maintain awareness of the pattern of pressure on the soles of my feet during stance, and to adjust this according to terrain and speed.  I do not run barefoot, except for short distances on grass, but do wear fairly light-weight shoes.

I regulate my level of energy expenditure largely by awareness of my breathing.  When breathing comfortably at a rate of one breath every six steps (about 30 breaths per minute),  I know I am in the lower aerobic zone, with minimal accumulation of acidity in my blood stream.  I can run for hours at this pace.  When my breathing rate increases to one every four steps, there has been mild accumulation of acid, but my body is dealing with it.  Nowadays I will be struggling after an hour at this pace, though a few years ago I could maintain this pace for about two hours.  When breathing rate becomes one breath every two steps, the acidity is accumulating rapidly.  This is only OK for the final stages of a race, or during high intensity intervals.

Some of these aspects of body awareness are well known to coaches and athletes; others, such as my focus on the down sweeping hand are experimental.  The over-arching principle is the cultivation of a holistic awareness of the sensations and movements involved in running, allowing for effort in the right time and place, while maintaining an overall sense of light, relaxed progress across the ground.

Final thoughts 

Here is John Woodward again, describing a workshop that he and his colleagues offer: ‘We perpetually stream down one route – the mechanical one: WE RUN MECHANICALLY. The aim of the workshop is to first and foremost stop the flow of traffic down the mechanical road the route well travelled. Like repositioning the points on the railway we want to initiate a flow down the road less travelled. This will enable the Thinking Gear to re-synchronize once more with the body. In this way we might begin to run creatively. There’s a number of key things about this invitation to re-route the traffic onto the road less travelled, the road to the present moment.’

I am not fully in tune with all of this statement.  I do not think we need to stop the traffic flow on the mechanical path.  I think the word ‘synchronise’ is the key concept. If we, as members of the species Homo sapiens, are to run truly naturally we need to find a way of synchronising the two routes: the mechanical path guided by knowledge and shaped by practice, and the path through sensations in the present moment.  I am still at the beginning of working out how this might be done.  My current experiments in running holistically might be clumsy, half-blinded attempts towards the goal.  I will value any comments.

Note added 12 April 2012

With regard to the proposal that it might be desirable develop a holistic sense of what is happening to the body, even though our attention is not focussed consciously on every aspect, there is a very informative picture in today’s Guardian newspaper, showing Prince Harry and Usain Bolt being silly for the sake of a photo-opportunity.  http://www.guardian.co.uk/uk/2012/apr/11/how-the-royals-became-cool   They are imitating a well known advertisement for Richard Branson’s company, Virgin. In the advertisement, Branson’s face is superimposed on Bolt’s body, as he mimes shooting an arrow from a bow.  In this Guardian photo of Harry and Bolt, note how the index finger of Bolt’s right hand is aligned perfectly with the index finger of his left hand.  I suspect he wasn’t consciously thinking about this as he posed for the photo.  Simply, his brain has an extremely good sense of where the ends of his limbs are at all times.  I think that is one of the reasons Bolt is the world’s fastest sprinter.  I think we can improve our running by improving our bodily awareness. In particular, awareness of the end of the index finger can probably associated with subliminal awareness of the location of the foot.

Is there a magic running cadence?

April 5, 2012

The six posts in my recent discussion of running mechanics, starting with my presentation of the equations of motion of the runner on 16th of January, have elicited 372 comments (including my own responses to the comments of others).  I have been delighted by the vigour of the discussion, but am intrigued by the fact that of these posts, the one which elicited the least comment was my post on the increased efficiency associated with increased cadence, on 6th February, which elicited only 5 comments.   I suspect that this relative paucity of comments reflects a widespread acceptance that increasing cadence does improve efficiency.  The major issues in the other five posts were related to the question of the push that is required to get airborne.  This appears to be a far more controversial topic.

From my own perspective, the controversy regarding push rather than cadence is a peculiar inversion of the uncertainties of running mechanics.  The fact that a large push is required to get airborne can be demonstrated by simple application of the laws of physics, and is readily confirmed by examination of force plate data.  A large vertical push makes it possible to minimise braking.  However, elastic recoil can produce at most 50% of the required energy for the push, so the vertical push is not cost free.  I suspect that the controversy about push exists because many runners, especially those who have adopted the Pose style, have found that they suffer less injury when they do not focus consciously on pushing.  Of course avoiding thinking about the push does not stop it happening.   But the evidence does suggest that avoiding thinking about it does reduce the risk of some common types of injury.  My own view is that denying the occurrence of a large push creates a different set of risks, and therefore I think that the challenging goal of developing a safe efficient running style is creating a mental image that allows a runner to avoid a mis-timed push and other associated unnecessary muscle activity, without the need to deny the existence of strong push.

The question of how to develop the optimum mental image is a question I will certainly return to in future.   The question that currently intrigues me is the apparently widespread acceptance that high cadence is generally good (a view that I myself advocate, but with reservations).  This view does not account for the clear evidence that most runners employ a relatively low cadence at low speed and increase as they increase speed.   While it is commonly believed that a cadence of 180 steps per minute (or 90 gait cycles per minute) is the optimum cacence, it is noteworthy that the representative runner depicted in figure 2 of Weyand’s paper (J appl Physiol, 89, 1991-1999, 200) increases cadence for about 144 steps per minute at a speed of 3.5 m/sec to 234 steps per minute at a speed 9.5 m/sec.  In my experience, these values are typical.   While many runners have a cadence around 140 steps /min or less when jogging, elite sprinters usually exceed 250 steps/min at top speed.   Therefore, the view that there is a target cadence of180 steps/min only corresponds very loosely with what runners do.

There is an optimum cadence for a given speed and peak vGRF

To estimate the most efficient cadence for a particular speed it is necessary to compute all three of the major costs of running: elevating the body, overcoming braking, and re-positioning the limbs.  While the combined costs of elevating the body and overcoming braking generally decrease with increasing cadence, the costs of repositioning the limbs increases with increasing cadence and also with increasing running speed (see calculations page, in the side bar, where I demonstrate that a fairly accurate estimate of the repositioing costs per Km per Kg body mass is given by 1.32CV Newton-metres where C is cadence in steps / min and V is running speed in metre/sec  ).  Therefore, for a given speed and peak value of vertical Ground Reaction Force (vGRF), there will be certain cadence at which the total energy cost will be minimised.  In other words, total energy costs decrease as cadence increases up to a certain point, but after the point at which the increasing cost of accelerating the swing leg outweighs the saving in the sum of elevation and braking costs, further increase in cadence will lead to greater costs.

Optimum cadence depends on ability to push

However, there is no single optimum value for cadence. The optimum cadence depends on one’s ability to exert a well timed strong push.  Elevation and braking costs decrease with increasing peak vGRF at a particular velocity, so the cadence at which the repositioning cost outweigh the elevation and braking costs at that velocity, will occur at a lower cadence in a runner who can exert a stronger push.  As the cost of accelerating the swing leg is lower at a lower cadence, peak efficiency will be greater in a runner who is capable of exerting a greater peak vGRF thereby achieving peak efficiency at lower cadence.  In other words, we can increase efficiency by developing the ability to exert a stronger push, provided the push is delivered at the right time and without producing unnecessary contraction of other muscles.

A comparison of age with youth

The computations that I presented on 6th February, clearly demonstrated that at a speed of 4 m/sec, the combined cost of overcoming braking and getting airborne is less at a cadence of 200 steps per minute than at 180 steps per minute, when the peak vGRF is 3 times body weight.  In fact, I myself adopt a cadence a little over 200 steps per minute at a speed of 4 m/sec, but most runners do not adopt such a high cadence at this modest speed.  I do so because, being a 66 year old with failing muscle strength, I find it difficult to exert a push against the ground of more than 3 times my body weight without straining.   Many younger athletes can easily exceed a peak push of this magnitude without consciously trying.  I am currently trying to increase my ability to achieve a stronger, well coordinated peak push, both by means of increasing my muscle strength, and also by improving the coordination of the push.

Recently Ewen pointed out on his blog that in setting the British 3000m indoor record of 7:40.99  in Glasgow in 2009, Mo Farah exhibited a cadence of only 176 steps/min in mid-race when he was covering each Km in about 2:35 (almost 6.5 m/sec).  He did increase to a cadence of around 187 in final few laps.

It appears that Mo is able to achieve a high efficiency at a relatively low cadence.  This demonstrates that he is capable of exerting an exceptionally strong, well coordinated push.

Conclusion

In summary, while the combined cost of elevation and braking decrease with increasing cadence, the cost of accelerating the swing leg increases with increasing cadence.  The total cost of elevation, braking and accelerating the swinging leg will decrease as cadence increases up to a certain limit, but beyond the point where rate of increase in swing costs outweighs the saving in elevation and braking cost, increasing cadence results in increasing cost.   A runner who is able to deliver a well-timed large push without simultaneously contracting unnecessary muscles can achieve peak efficiency at a relatively low cadence.

Natural running

March 29, 2012

The word ‘natural’ invokes images of wholesomeness but also carries a hint that we are in danger of being hoodwinked by a snake-oil merchant.  In contrast, the word ‘technological’ has overtones of something lacking wholesomeness.  Nonetheless, on the whole, I am glad I belong to a species with the brainpower to develop technology.   Many inventions created by human wit, ranging from reading glasses to electronic devices, extend the range of activities that are accessible to me and make life more interesting.  But when it comes to running, there is good reason to ask whether we have lost our natural skill as a result of growing up a modern technological society.

Humans are in fact remarkably good endurance runners.  Although many species can outpace us in a short sprint, few can maintain a steady pace for such long distances. On the other hand, a very large proportion of us get injured each year.  In a comprehensive review of studies of injury rates among distance runners, van Ghent and colleagues found that the incidence of lower extremity injuries reported in published studies ranges from 20% to 79% (Br J Sports Med 41: 469-480, 2007).

Persistence hunting

Accumulating evidence suggests that humans became good endurance runners because evolution favoured the development of anatomical (and perhaps biochemical) adaptations that enabled our forebears to engage in persistence hunting – in which the hunter pursues his quarry to the point of exhaustion – on the African savannah around two million years ago. (Bramble and Lieberman, Nature, 432, 345-352  2004).   We do not know whether or not early persistence hunters were also prone to injury, though evolution would scarcely have favoured those who were as prone to injury as modern-day runners. Perhaps only an elite few in the tribe were able to run without injury.  Among the few remaining peoples of the Kalahari desert who continue to practice persistence hunting today, the huntsman who engages in the long chase is an elite member of the hunting group.  Nonetheless, an ability to run far with few injuries is likely to have been a fairly common skill among our early ancestors.

Bare feet v shoes

So if we wish to minimize injury, it is probably worthwhile to ask how did our forebears run.  Perhaps the first point to note is that they would not have worn shoes (though it is also noteworthy that  modern-day persistence hunters in the Kalahari do wear shoes).  The most striking difference between barefoot and shod runners is the nature of the foot-strike.  Hasegawa and colleagues demonstrated that about 75% of runners wearing modern running shoes heel-strike (J Strength Cond Res. 21(3):888-93, 2007).  In contrast, Lieberman and colleagues have demonstrated that bare-foot runners are much more likely to land on the forefoot and then transfer a portion of the load to the heel whilst on stance.  Lieberman and colleagues have demonstrated this is a systematic study comparing American habitual barefoot runners with shod runners, and confirmed it in a less systematic observation of Africans who had grown up never wearing shoes (Nature. 463(7280):531-5, 2010.   Landing on the forefoot minimises the initial sharp increase in vertical ground reaction force that is seen with heel striking.

Lieberman is firm in pointing out that there is no strong evidence that minimising this sharp increase in ground reaction force leads to lower injury risk. However, in general, the repeated application of a rapidly rising large force is stressful and might be expected to lead to stress fracture.  So it is plausible that injury risk is greater when wearing shoes. This plausibility is confirmed by Kerrigan’s demonstration of greater torques at hip and knee during shod running (PM &R: The Journal of Injury, Function and Rehabilitation, Vol. 1, pp 1058-1063, 2009).  Thus it appears that Bill Bowerman’s first experiments with a waffle iron that led to the modern running shoe, were a faltering mis-step based on the mistaken idea that putting padding between the runners foot and the ground would increase safety and efficiency.

Getting airborne

I have discussed the question of running shoes and foot-strike in a previous post, and I will probably return to it again in the future.  However my main interest today is in the question of how our forebears were equipped to deal with the cardinal challenge of running: exerting a strong enough force to get airborne.  Getting airborne is the essence of running.  It allows us to minimise the inefficient braking that is an inevitable consequence of maintaining a stationary foot on the ground during the stance phase.  To minimise braking we must spend as small a portion of the gait cycle on stance as is possible.  We can do this by landing with the foot only a short distance in front of our centre of gravity (COG), but that necessarily entails the exertion of a large push against the ground.   If we are on stance for only a third of the gait cycle, the average push against the ground during stance must be three times body weight.

A substantial part of this push is generated via elastic recoil.  But in fact, measurements suggest that at most about 50% of the required energy can be generated by elastic recoil (Alexander, R.M. Energy-saving mechanisms in walking and running. J.Exp.Biol.160,55–69,1991).  So an equally substantial portion of the work must be done by an active push.   What evolutionary development allowed early member of the homo genus to achieve this crucial push?  A clue can be found by examining the anatomical differences between ourselves and our nearest primate relative, the chimpanzee.  Chimps, like other non-human primates, are not capable of endurance running.

Differences between man and chimp

The most immediately apparent anatomical difference is man’s larger skull.  However, the larger skull is a feature of homo sapiens rather than early members of the homo genus.  Possibly we owe our large skull and brains  at least in part to a somewhat more subtle change at the lower end of the vertebral column that occurred earlier in homo evolution.  This subtle change, present in early members of the homo genus, such as homo erectus, is a substantial enlargement of the upper part of gluteus maximus.  Gluteus maximus is a hip flexor.  Although it acts with less mechanical advantage than the hamstrings, it is more massive   Could the enlargement of gluteus maximus have played a key role in the development of endurance running ability, thereby facilitating persistence hunting and providing the protein rich diet essential for the eventual development of homo sapiens’ large brain, over a million years later.

The roles of gluteus maximus

To address this question Lieberman and colleagues  examined the activity on gluteus maximus throughout the gait cycle, by recording the electrical signals from an electrode placed over the muscle, during both walking and running (Journal of Experimental Biology 209, 2143-2155, 2006.)  Their  first important  observation was that gluteus maximus is much more active during running than walking, consistent with it being an evolutionary development associated with the acquisition of capacity for endurance running.  During the running gait cycle, there are two main bursts of activity in gluteus maximus: one when the foot from the opposite side of the body is on stance and the other beginning shortly before the footfall of the foot on the same side as the muscle,  and continuing through early stance on that foot.  The activity when the opposite foot is on stance almost certainly reflects the action of arresting the forward motion of the swinging leg.   Interpretation of the role of the burst of activity in early stance on same-sided foot is more complex.  The magnitude of the activation increases with speed of running and is also correlated strongly with the velocity and timing of the forward pitch of the trunk that occurs at foot-strike.  Thus it is very likely that a major role of gluteus maximus is stabilizing the torso.

Mark Cucuzella’s resonant phrase ‘you can’t fire a cannon from a canoe’ powerfully expresses the importance of stabilization of the torso, but it also raises the question of what cannon is being fired.   Could gluteus maximus also contribute to generation of the vertical ground reaction force (vGRF) that launches the body forwards and upwards from stance?   Lieberman and colleagues  observed that the timing and magnitude of activity in gluteus maximus is also correlated with the timing and magnitude of contraction of another major hip extensor, biceps femoris, which is one of the hamstrings.    This suggests an active role in hip extension.  It is important to note this active hip extension is largely confined to the early part of the stance phase.  As the hip and knee are slightly flexed at that time, the main consequence of hip extension will be an increase in the downwards push against the ground.   Thus, this action would be expected to contribute to the initiation of the upward acceleration of the body commencing in mid-swing. Perhaps gluteus maximus also contributes to firing the cannon.

It is noteworthy that one of the early proponents of ‘natural’ running, Ken Mierke, recognised that combining contraction of gluteus maximus with the hamstrings would greatly increase the power of hip extension, thereby reducing fatigue of the relatively weak hamstrings and promoting endurance.  While I think that the essence of Ken’s proposal is sound, I would place a somewhat different emphasis on the effect of the hip extension.  Ken argues that the hip extension largely provides forward propulsion.  I do not think that fits well with the timing of the active contraction of either gluteus maximus or the hamstrings.  Even after allowing for the 40-50 millisecond delay between the electrical signal and the mechanical effect of a muscle contraction, the active contraction of gluteus maximus and the hamstrings is complete shortly after mid-stance.   I think that the main consequence of this powerful hip extension is to accelerate the body upwards thereby achieving a stance that is short – this is the key requirement for efficient running.

Other muscles also contribute, notably contraction of the gastrocnemius, which reaches its peak contraction a little later in stance.  This will generate a forward and upward GRF.  The upward component will add to the impulse that gets us airborne, while the forward component will help compensate for the braking that occurred in early stance.  Because the hamstrings cross both hip and knee, residual tension in the hamstrings in late stance might add to the upswing of the lower leg relative to the torso thereby facilitating the breaking of contact.  However it should be noted that the contribution of a hamstring to pulling the foot towards the torso cannot contribute to raising the centre of mass of the body (as is proposed in Pose theory).  That would be pulling oneself up by ones bootstraps.  The upwards acceleration of the mass of the body must be produced by a push against the ground.  (Added note: it should be acknowledged that Pose theory appears somewhat ambiguous regarding the mechanism by which the centre of mass is raised.  See the comments from Hans and Jeremy below.)

Other evolutionary developments

Development of gluteus maximus was not the only anatomical change occurring early in the evolution of the genus homo.  Freeing up of the tethering of head to shoulders that limits the independent rotation of upper torso and head in other primates, allows us to produce the counter rotation of the torso necessary to balance the swinging leg, while maintaining the head upright and forward-facing.  In addition, the development of a longer Achilles tendon that occurred at some point along the evolutionary path from our even earlier ancestor, australopithecus, to early homo species, is likely to have enhanced the efficiency of capture of impact energy as elastic energy.   But in my opinion, it was the development of gluteus maximus that was the decisive development that allowed us to get airborne efficiently.

Minimizing risk of injury

While these speculations might explain how our forebears came to be efficient endurance runners, it still leaves us with the question of how we might avoid injury in the face the inevitably large vertical ground reaction forces generated by the powerful push.  I think that Kerrigan’s  demonstration of greater torques at hip and knee during shod running is a key observation.  This suggests that the orientation of the foot on the ground during the period around mid-stance when vGRF is at its peak is likely to play a major part in determining how much torque is produced.  Drills that help develop a sharp contraction of gluteus maximus that is well coordinated with the down swing of the contralateral arm will ensure that the non-conscious brain is well appraised of just when the peak vGRF will occur.  In addition, an appropriate  sharing of weight between forefoot and heel at mid-stance facilitated by  shoes that are light enough to allow a good perception of the distribution of ground reaction forces might allow the non-conscious motor control system in our brain  to coordinate the application of the push in a way that minimises potentially damaging torque at the knee and hip.

Conclusion

We have grown to adulthood spending hours each day sitting at a desk or in an automobile seat, and even longer periods with our feet encased in rigid shoes.  If we are to run naturally, in a style similar to that which allowed our early homo ancestors to master the art endurance running, perhaps we should focus on re-training our bodies so that our non-conscious brains can once again integrate the sensory signals from the joints in our arms and legs, with those from the numerous sensory nerve terminals in our feet, to coordinate the delivery a powerful, well-timed but fairly safe push against the ground to get us airborne.

Training to increase sprinting speed

March 15, 2012

The issues raised by Klas in his comments on my recent post on Usain Bolt’s sprinting style have led me to wonder just what it is that determines peak sprinting speed and what a runner might do to increase sprinting speed.

The key relevant scientific study is the investigation of 33 physically active adults (aged between 18 and 36) of varying sprinting ability, published by Peter Weyand and colleagues from Harvard University in Journal of Applied Physiology (J Appl Physiol, 89: 1991–1999, 2000).  They measured characteristics such as cadence, time on stance, swing time and ground reaction force observed across a range of speeds up each individual’s top sprinting speed.  The range of top speeds extended from 6.2 metre/sec up to 11.1 m/sec.  They observed that the faster sprinters exerted a stronger push on the ground while on stance and concluded ‘runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground’.

I agree with their conclusion, but closer inspection of their data leads me to a slight modification that might have important implications for how a runner should train to increase speed.

Limb repositioning time

First let us consider the time taken to reposition the swinging leg from its position behind the centre of gravity (COG) at lift-off from stance, to a position a little ahead of the COG at foot-fall.  This is the swing time.  It embraces two airborne intervals and a period of stance on the other leg.  Perhaps surprisingly, the swing time at top speed varies very little between runners of markedly different sprinting ability.  The average swing time of the 33 runners was 0.38 seconds with only weak evidence that faster runners have a shorter swing time.  For comparison, the average swing time of the three medal winners in the male 100m at the 1996 Olympics was 0.33 sec.  However, there is little evidence of a consistent trend across the range of sprinting ability.  For example, the slowest of the 33 individuals studies by Weyand had a swing time of 0.34 sec despite running only a little faster than half the speed of the fastest runners.

Although faster runners spend less time on stance, because their speed is greater, the foot gets left further behind during stance. Typically, a slow runner has to move the foot forward by about 85 cm relative to the COG during the swing, while the fastest runners have to move the foot forwards by about 105 cm.  Thus, the faster runners do swing their foot forwards a little faster. For an elite sprinter it is worthwhile expending some effort on improving swing dynamics, for example by flexing the knee to create a short lever arm at mid-swing.  However, this is only fine tuning – perhaps it might make the difference between a gold medal and fourth place, but it is not likely to produce the magnitude of improvement that might encourage a recreational distance runner to choose to become a sprinter instead.

It is interesting to wonder why swing time at top speed varies so little between elite sprinters and non-athletes.  It appears that most of the gain a  faster sprinter derives from increased ability to reposition the foot rapidly relative to the COG is required to compensate for the modest increase in the range of the swing required at higher speed.  It appears to be impossible to get swing time appreciably below a third of a second.  Although the swinging leg is not merely a passive pendulum it is hard to drive it much faster than its natural swinging rate

Time on stance

The strongest predictor of top sprinting speed is ability to get off stance rapidly.  In Weyand’s study, the slowest sprinters spent 0.135 sec on stance while the fastest spent about 0.09 sec on stance.  Furthermore, there was a very consistent trend for decreasing time on stance to predict faster top speed, across the full range of sprinting ability. The correlation between stance time and top speed was 0.76.

Shorter time on stance is associated with stronger push against the ground.  The average vertical ground reaction force (vGRF) during stance increased from 1.9 times body weight to 2.4 times body weight, although the relationship was not quite so consistent across the range of top speeds.  The correlation between average push and top speed was 0.62.  Thus the average vGRF while on stance was not quite such a reliable predictor of top speed as stance time.

It is of interest to note that because stance time decreases as strength of push increases, the impulse delivered (product of force by time for which the force acts) varies relatively little between the slower sprinters and the fastest.  The vertical impulse was 2.49 newton-sec at a top speed of 6.2 m/sec and 2.25 newton-sec at a top speed of 11.1 m/sec. As the vertical impulse determines how much upward momentum is imparted to the body, it determines how high the COG is elevated between mid-stance and mid-flight. .The peak elevation of the COG was marginally lower in the fastest spinters.  The precise gain in elevation from a given impulse depends on the shape of the relationship between force and time while on stance. . For a forefoot runer it is approximaltey sinusoidal and in this case, the range of vertical oscillation of the COG was 5 cm at 6.2 m/sec and 4.3 cm at 11.1 m/sec.

Estimated values for slowest and fastest runners based on linear trends across the group of 33 runners. *The calculation of peak vGRF and elevation assumes a sinusoidal variation of vGRF with time during stance – typical of a forefoot runner

Conclusion

These observations indicate that if one wants to sprint faster, one should aim to increase push and decrease time on stance.  Although these two variables are related, in fact the decrease in time on stance is a stronger predictor of peak speed than the magnitude of the push.  This is not surprising because decreased time on stance directly reduces braking, which leads not only to increased fuel efficiency, as discussed in my post on 16th January, but also to more efficient utilization of peak power.

It is necessary to have strong leg muscles to get off stance quickly, so it is worthwhile training so as to increase leg strength.  As eccentric contraction is required, plyometrics are potentially helpful. However, the fact that the ability to get off stance quickly is the strongest predictor of top speed, suggests that one requires not only adequate strength but also good coordination of the muscles so as to capture impact energy as elastic energy and then release that energy in a smoothly coordinated way.  This conclusion is similar to that reached on the basis of considering the style of Usain Bolt.  If I want to increase my sprint speed I should focus not only on increasing my strength, but also my coordination.

I suspect that genes and development during infancy play a large part in determining how quickly a person can get off stance.  Nonetheless, the fact that top speed decreases with age demonstrates that top speed is not fixed, and suggests that a training program aimed at producing changes opposite to those produced by aging might produce an increase in sprinting speed.

How might I increase my coordination?  Plyometrics are likely to increase coordination in addition to increasing strength, though they are risky, and should be performed in moderation.  A more direct focus on coordination might be worthwhile.  Coordination depends on proprioception  (the ability to sense  where ones limbs are) and the ability to send messages from the central nervous system to the muscles with the appropriate  precise timing.  I believe that drills such as ‘change of stance’ are likely to be an effective way to achieve this


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