Archive for April, 2013

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.

Base-building for a half marathon/marathon

April 21, 2013

I need once again to re-build my aerobic base.   Last year, I enjoyed a year free of ill-health, and after averaging a little over 40 miles of predominantly low aerobic training each week in the spring and summer, was pleased to run half marathon in 101:50.  By mid-summer it appeared that I was mainly limited by lack of strength rather than aerobic fitness.  Therefore, following the half-marathon, I began regular resistance sessions: three sessions per week in which the major focus was on 5 sets of 5 squats with the goal of building up my 5 RM to at least 150% of body weight.  Although I did not know it at the time, Alberto Salazar had set a very similar target for Mo Farah in preparation for the London Olympics.  Mo achieved a 5 RM of 200lbs for squats.  My program of lifting went well, and to my amazement, I built up to a 5 RM of 230 lbs over a period of four months.  Since I am a little lighter than Mo and substantially more than twice his age, I felt quite pleased with my progress.  I am afraid that I will no longer be able to blame my atrophied elderly muscles for my poor running speed.  Furthermore my creaky joints appeared to cope with the lifting well.  By the end of the year I had less arthritic pain than at any time in recent years. So I was looking forward to redirecting my focus onto running in the new year

However, shortly after I started running again, my former arthritis returned.  As on previous occasions, the problem started in my neck and left wrist, before extending to my knees, so I do not think it can be attributed directly to the impact at foot-strike when running.  I do wonder whether running led to a build-up of circulating inflammatory molecules in the blood stream that inflamed the joints, but that is speculation.  The unfortunate consequence was curtailed training and loss of fitness.  In recent weeks, my joints have settled and now only my neck is painful – though my knees still feel fragile.  But my endurance and aerobic capacity have deteriorated.  I have deferred my target of a sub-100 minute half marathon in the spring to the autumn.

So once again I am facing the cardinal question: what is the best training strategy for base-building?  For an endurance runner, a sound base has two key components: resilience of the connective tissues (ligaments, tendons, bones, fascia) and ability to utilise fuel efficiently.   The simple rule of thumb for building up resilient connective tissues is a gradual increase in volume and intensity of training over a sustained period, though there is a paucity of detailed information about this topic.   On the other hand, there is abundant information about the topic of improving the efficiency of fuel utilization, but some crucial issues remain a topic of debate.

The major determinant of endurance running performance is the maximum pace that can be sustained without accumulating appreciable lactic acid.  Loosely speaking, that is the pace at lactate threshold.  The problem with this terminology is that there is no precise threshold. Although lactate level in the blood begins to rise fairly rapidly after a certain point, the graph of lactate concentration against pace does not show a single sharp kink between two straight lines. Instead there is an initial upward trend typically occurring at a lactate concentration above 2mMol and then a steeper up-slope beyond 4 mMol.   From the practical point of view, there are two fairly clear thresholds.  The first corresponds to maximum pace that can be sustained for several hours (provided your connective tissues have the necessary resilience, and you can avoid running out of glucose).  At this pace, the rate at which lactate is cleared from the blood matches the rate at which it is produced.  Typically this is at a lactate level of 2 mMol.  Roughly speaking, this is marathon pace.   Because blood acidity is a major influence on the urge to breathe, it also corresponds approximately to the point at which breathing becomes a noticeable effort.  Because I link my breathing rate to my step rate, I become aware that I have crossed this ‘aerobic’ threshold when I find I am more comfortable taking one breath every 4 steps rather than one breath every 6 steps. This ‘aerobic’ threshold is what Hadd refers to as the lactate threshold.

The second threshold is the pace beyond which lactate builds up to an intolerable level on a time scale measured in minutes.    I know I have crossed this ‘anaerobic’ threshold when breath rate increases to one breath every two steps – but I avoid this except in the final few hundred metres of a race (or occasionally on steep hills).     Races from 5K to HM are run at a pace somewhere between the aerobic and anaerobic thresholds, while the marathon is run at aerobic threshold.  So for the endurance runner, the success of the base building phase can best be quantified by measuring the pace at aerobic threshold, or as Hadd described it, the pace at lactate threshold.

Capillaries and VEGF

To re-iterate the key point, the late threshold is the point at which the rate of removal of lactate balances the rate of generation of lactate.   Therefore, a major goal of base-building is reducing the rate of generation of lactate.  Since no lactate is produced when fuel is metabolised in the presence of sufficient oxygen, the first requirement is delivery of a copious supply of oxygen to the muscle.  This requires enhancement of cardiac output and the development of capillaries in the muscle.  Both of these developments will be enhanced by running at a pace that is adequate to place the heart and muscles under some stress, but not too much.  The production of various growth factors, such as Vascular Endothelial Growth Factor (VEGF) that is responsible for stimulating the development of new capillaries, is promoted by a shortage of oxygen, so a degree of oxygen deprivation is required to maximise the development of capillaries.   The first major challenge is determining just where this ‘goldilocks’ level of stress occurs.    The answer is still a  matter of controversy, but before attempting to answer it, we need to consider several more issues.

Oxidative enzymes in mitochondria

Maximising power output at lactate threshold also requires the development of the oxidative enzymes in mitochondria that carry out the process of burning fats or glucose, and transferring the energy released to the high energy molecule, ATP, that is the direct source of energy for muscle contraction.   The required development of oxidative enzymes will occur if the system is appropriately challenged.  Running in the aerobic zone stimulates the development of oxidative enzymes, but it is also of interest to note that High Intensity Interval Training (HIIT) also leads to increased production of mitochondrial oxidative enzymes.

Removing lactate

In order to minimise accumulation of lactate when running near the threshold, we also need to maximise the ability to remove lactate.  This is done by a process that converts lactate back to glucose in the liver.  The process of transporting lactate to the liver, conversion to glucose and then transporting it back to muscle where it can be used again as fuel, is known as the Cori cycle.  It is likely that training at a pace that generates at least a moderate level of lactate will promote development of the enzymes of the Cori cycle.   However, the Cori cycle is not a source of ‘cost-free’ energy for muscle because conversion of lactate to glucose in the liver consumes energy.  Therefore, while it is beneficial to develop the enzymes of the Cori cycle, it is far more effective to minimise the production of lactate in the first place.

So far, the various issues we have considered emphasize the importance of training at a sufficiently high intensity to produce adequate stress on the system to stimulate production of growth factors such as VEGF; enzymes such as the mitochondrial oxidative enzymes and to a lesser extent, the Cori cycle enzymes.

The recruitment of different types of muscle fibre

However, this is only one side of the equation that must be balanced.  Muscles contain slow twitch and fast twitch fibres. The slow twitch fibres are specialised to function aerobically for long periods at low intensity. The fast twitch fibres are designed to generate high power output for a relatively brief time.  The fast twitch fibres occur in two types: aerobic and anaerobic.  The anaerobic are capable of generating the power needed for explosive movement.  They can develop power on a time scale that is rapid compared with the delivery of oxygen to tissues.  For this purpose, fuel efficiency is usually less important that speed of contraction.  These fibres generate their ATP via the rapid but uneconomical conversion of glucose to lactic acid.   Thus, when the anaerobic fast twitch fibres are engaged, acidity develops rapidly.

However, the nervous system is canny in the way it recruits muscle fibres.  As the requirement for increased power output increases, fibres are recruited in the order: slow twitch, aerobic fast twitch and finally anaerobic fast twitch.  At low power, slow twitch fibres are recruited and little acidity is generated.  Training at an intensity that puts a little bit of pressure on the slow twitch fibres will lead to further development of capillaries and mitochondria, thereby providing an increase in the power output that can be generated by these fibres.

If at the other extreme, you demand that your muscles generate a high power output, the anaerobic fast twitch fibres are recruited and the muscle is flooded with lactic acid.  Acidity makes muscle contraction less efficient and ultimately, the muscles shut down. It appears that the slow twitch fibres shut down first, although do not know of direct evidence for this,.  Whether or not the slow twitch fibres shut down first, when you run at a pace that preferentially recruits the anaerobic fast twitch fibres there is little opportunity for the prolonged activity that promotes the development of mitochondrial enzymes in slow twitch fibres.

Two options for increasing oxidative capacity

An unresolved  issue of major practical importance is what happens if you do multiple brief bursts of high intensity activity, separated by recovery periods in which lactate is cleared, as in high intensity interval training.  As mentioned previously, measurement of mitochondrial oxidative enzymes before and after HIIT reveals an increase in  oxidative capacity.  The question of whether this occurs preferentially in aerobic fast twitch fibres or occurs also in slow twitch fibres is not clearly established.  Nonetheless, if you want to increase oxidative capacity, you have two options: run slowly, though the gains are likely to be most rapid near to the point where appreciable recruitment of fast twitch fibres begins; or do high intensity interval training in which the recovery intervals are sufficient to clear lactate between the effort epochs.

Developing fat utilization

However, we should not focus only on developing the capacity to metabolise glucose.  At least in longer races such as the marathon, it is essential to derive a substantial proportion of the required energy from fat, simply because the glucose supply is inadequate.   The amount of energy that can be derived from fat increases up to a certain power output, but then decreases rapidly to near zero.  The power output at which the maximum rate of fat utilization is achieved varies between individuals, though on average, in trained athletes it occurs at around 63% of VO2max.  However, the level at which maximum fat utilization occurs can  be increased by appropriate training (and perhaps also by diet).  A marathon runner will be limited to an average pace that is not much greater than the pace at which maximum fat utilization occurs.  Therefore, in preparation for a marathon, increasing the proportion of VO2max at which fat utilization is maximal, is crucial.

Although several key questions remain unanswered, the above considerations provide a basis for rational planning of base-building.  In my next post I will address the question of the optimum practical strategy.