Archive for December, 2016

Polarized Training and Injury Prevention

December 29, 2016

Avoiding injury is one of the major goals of training for distance running.  On account of the impact forces experienced at footfall on every stride, runners are uniquely prone to injury.  However, effective strategies for preventing injury are elusive.  In recent years, advocates of techniques such as Pose have claimed that injuries are largely due to poor running technique, and have promised that the problem can be overcome by proper technique.  In particular, they have identified heel striking as a cardinal problem.  However, there is very little evidence to support this claim.   Others have advocated stretching during warm-up as a strategy to reduce risk of injury, though the evidence provides little support for this claim.  Advocates of barefoot running have proposed that running shoes are the problem, but again there is little evidence to support the claim that running barefoot or in minimalist shoes reduces risk of injury.  Conversely, the manufacturers of running shoes have placed blame on foot orientation problems such as over-pronation and claimed that motion control shoes can reduce this risk.  Yet again, the evidence is slight, though at least one study had found that over-pronation is associated with increased risk of injury.

It is likely that a wide variety of factors contribute to injury in different individuals.  Meta-analyses that pool the findings of many studies are only likely to identify risk factors that are common to many athletes.  Two risk factors emerge consistently: a history of previous injury; and a large weekly volume of training.   Lisa Callaghan has provided an up-to-date review of the evidence.

Prior injury

A history of previous injury might predispose to subsequent injury simply because the athlete has not corrected problems that contributed to the first injury.  It is also possible that unsatisfactory recovery from the previous injury plays a role.  Muscles, tendons and other connective tissues tear when subjected to force that exceed the limits of their resilience.  A cardinal factor in the resilience of connective tissues is the elongated spring-like structure of collagen fibres, making them resilient against forces acting along the direction of the fibre.  During the initial stages of repair following injury, collagen is laid down with random orientation providing a framework for tissue renovation, but full resilience requires remodelling such that the collagen fibres become aligned in the required direction.  Therefore effective recovery requires early mobilization to promote the laying down of appropriately aligned fibres, perhaps augmented by slow stretching.

Training volume

Observational studies report that training volumes of 65 Km (40 miles) or more per week are associated with higher rates of injury [Fields et al; van Ghent et al].   In part these observations might simply reflect the greater duration of exposure to risk of injury, though it is likely that fatigue plays an important role.   In particular fatigue impairs neuromuscular coordination increasing the likelihood of poor coordination between different types of muscles fibres within a muscle and poor coordination between muscles that act as agonists and antagonists, resulting in excessive local forces within tissues.

Polarized training

Simply limiting training volume is unlikely to be a satisfactory strategy for many runners, making it desirable to identify alternative strategies to reduce the damaging effects of fatigue.  As the forces exerted increase with increasing pace, it might be expected that injury risk would be greater at faster paces. However the observation by Van Middelkoop and colleagues that among marathon runners, those who do interval training have a lower risk of knee injury raises an intriguing question.  Could it be that interval training provides greater protection than training at   somewhat lesser paces in the vicinity of lactate threshold?   Interval training, in which short efforts at fast but sub-maximal pace are separated by recovery periods, tends to promote the development of neuromuscular coordination with relatively mild muscle fatigue.  As discussed in my recent post, interval training is likely to promote a favourable balance between anabolic and catabolic hormones, leading to strengthening of tissues. In contrast, running for a sustained period at threshold pace might produce fatigue with the associated risky deterioration of neuromuscular coordination during the session, and also tip the balance towards the catabolic effects of cortisol, promoting subsequent breakdown of tissues.

Even more speculatively, the viscoelastic character of the musculotendinous unit might result in a peak risk of damage to muscles and tendons at threshold paces. Viscoelastic materials offer strong resistance to brief sudden onset forces but less resistance to sustained forces.  Although force is greater at sprinting pace, time on stance decreases.  At speeds above LT there is actually a decrease in the impulse acting through the foot at each step because the increased force is more than compensated by  reduction in time on stance.  The product of forces x time on stance actually decreases, as illustrated in figure 1 based on data from the study by Weyand and colleagues.

ImpactForce&Impulse

Figure 1. Upper panel: the average vertical force (expressed relative to body weight) during stance as a function of running speed. Lower panel: the vertical impulse (average force x duration of stance) transmitted through the leg during stance as a function of running speed.

Thus, it is possible that the risk of tissues tearing is actually less at sub-maximal paces substantially above LT than in the vicinity of LT.   Nonetheless, it is crucial to prime the requisite neuromuscular coordination during the warm-up (for example by moderate intensity strides) and it is generally desirable to avoid absolutely maximal effort that taxes neuromuscular coordination to the limit, during training.

The other pole of polarised training is low intensity running.  This has the potential to build resilience of the muscles, tendons and the other connective tissues engaged during running by repeated application of moderate forces.   Provided training volume is built-up gradually and excessive fatigue is avoided, the risk of injury is low.

Conclusion

While the predisposing and precipitating factors causing running injuries remain controversial, consistent evidence indicates that a high weekly training volume increases the risk.  In contrast, the observation that interval training provides some protection suggests that polarised training might diminish the risk.  Observational evidence and also speculation based on principles of biomechanics and physiology suggest that high intensity sessions have the potential to build effective neuromuscular coordination, while low intensity training would be expected to enhance the resilience of muscles, tendons and other connective tissues with relatively little risk.  Nonetheless, as with any type of training, it is important to build up the training load gradually, and to warm up for each session in a manner the primes the requisite neuromuscular coordination.

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How does polarised training minimise lactate accumulation?

December 23, 2016

My previous post discussed evidence indicating that training in the vicinity of lactate threshold (LT) can lead to sustained elevation of cortisol which has the potential to damage to the neuromuscular system and suppress immune responses.  In particular, the study by Balsalobre-Fernandez indicates that frequent training at or a little above lactate threshold is more damaging than a lesser amount of training at a higher intensity.   This might be the key to understanding why a growing body of evidence favours polarized training, which includes a large volume of low intensity training, a small amount of high intensity training and a similarly small amount of threshold training,  in preference to a training program with a higher proportion of threshold training.

As distance races from 5 Km to marathon are raced in vicinity of lactate threshold, pace at LT is a crucial determinant of performance.  Enhancing the ability to delay the onset of lactic acid accumulation as pace increases is one of the key goals of training.   The effectiveness of polarised training raises the question of how a program with only a small about of threshold training might nonetheless be effective in enhancing ability to minimise lactate accumulation.

Lactate accumulation might be minimised by decreasing the rate of production and /or increasing ability to remove it.  The rate of production can best be minimised by increasing the capacity to generate energy aerobically, which in turn might be enhanced by increasing the capacity of aerobic enzymes in mitochondria and/or increasing delivery of oxygenated blood to muscles.

Developing Aerobic Capacity

While a large volume of low intensity running would be expected to increase the aerobic enzymes in slow twitch fibres, the more challenging question is how to enhance the aerobic capacity of fast twitch fibres.  Low intensity running beyond the point of exhaustion of slow twitch fibres might help achieve this, but frequent very long runs create the risk of excessive stress.   For many years followers of Arthur Lydiard’s approach to periodization, in which the base-building phase is almost exclusively devoted to relatively low intensity aerobic running, have  maintained that when you bring speed work into the program, you halt the development of aerobic enzymes. The size of the engine is now fixed; the task of speed work is to tune this engine.

This claim was associated with a widespread belief that the acidity generated above LT prevented development of aerobic enzymes, and perhaps even damaged them.   This belief is ill-founded.  Extensive research into high intensity interval training (HIIT) in recent years has demonstrated that HIIT is a very efficient way to increase the capacity of aerobic enzymes.  The available evidence indicates that HIIT achieves the enhancement of mitochondrial enzymes via the increasing the activity of the messenger molecule, PGC-1alpha, the same messenger as  appears to mediate mitochondrial development in response to lower intensity endurance training

HIIT research is largely focussed on comparing high intensity training with low intensity training and has not so far investigated the potential benefits of a polarised approach.  It would be anticipated that in a polarised approach the rate of gain in aerobic capacity would not be a rapid as with HIIT, but it is scarcely credible that diluting the high intensity session with low intensity sessions would abolish  the aerobic gains of the high intensity sessions, provided there is adequate opportunity for recovery.

Not only does HIIT produce efficient development of aerobic enzymes, but it is also effective in enhancing the development of the enzymes that metabolise fats, thereby promoting the generation of energy from fat, a processes that does not generate lactate

With regard to increasing the supply of oxygenated blood to muscle, sprint interval training is as  effective as endurance training in promoting development of capillaries.  Although the effect of HIIT on development of cardiac output has been less thoroughly studied, it is noteworthy that the Gerschler’s rationale for the introduction of interval training was the stimulation of cardiac output.  In his word interval training provides “a stimulus particularly powerful to reach the heart.”

Transport of lactate

The alternative approach to minimizing lactate accumulation is removal of lactate from muscle and blood.  With regard to the relative efficacy of polarised training compared with threshold training, the important issue is whether or not this is better promoted by brief surges of intensive lactate production or by sustaining a moderate level of lactate.   The mechanisms by which lactate is removed from muscle include the transport of lactate from fast twitch fibres, where it is produced, to slow twitch fibres, which have the capacity to metabolise the lactate; the transport to other organs such as heart muscle which are well adapted to metabolising lactate; or transport to the liver where the process of glycogenesis converts lactate to glucose and subsequent storage in the form of glycogen.

The transport of lactate across cell membranes is mediated via a set of transport molecules, the monocarboxylate transporters (MCTs) that transport lactate together with protons.  Transport by MCT’s involves diffusion and the rate is determined by the transmembrane gradient of either lactate or acidity (protons).  It is likely that under most conditions, lactate flux is determined mainly by the gradient produced by metabolism-driven uptake, while the availability of MCTs is rate-limiting only after the establishment of large transmembrane gradients.   Therefore, the first goal in enhancing the capacity to clear lactate during distance running is enhancing the ability to metabolise lactate. In heart and slow twitch fibres, this is achieved by enhancing vascularization and aerobic enzyme activity.  The evidence discussed above suggests that polarized training is an effective way to do this.  Nonetheless, it is desirable to ensure that MCT’s are maintained at an adequate level. Because  MCT-mediated transport is rate-limiting only in the presence of large transmembrane gradients, it would be expected that brief surges of lactate  will be more effective in promoting development of MCTs than sustained moderate levels.

Buffering of acidity

The role of acidity in stimulating training effects is ambiguous.  On the one hand rising acidity eventually halts metabolism in muscle, but on the other, some degree of stress is likely to be necessary to promote adaptation.   Ingestion of sodium bicarbonate (baking soda) which neutralises acid has been shown to diminish the secretion of anabolic hormones, such as growth hormone, following intense exercise. Thus rise in acidity appears to facilitate at least some of the desired effects of training.  In contrast, sodium bicarbonate ingestion augments the increase in activity of the messenger molecule PGC-1alpha in skeletal muscle during recovery from intense interval exercise in humans, and therefore might promote the development of mitochondria.

This raises the question of the role of natural buffering mechanisms in the blood.    During intense exercise there is a transient rise in the body’s natural buffers, phosphate ions and bicarbonate ions, that helps neutralise the rise in acidity despite the rise in lactate concentration.  Thus it is plausible that one of the advantages of interval training compared with threshold training is that the transient natural buffering during interval training allows more intense exercise and hence allows greater lactate production without excessive acidity.    Perhaps this would act as a greater stimulus to PGC-1 Alpha activity and perhaps MCT production as well. On the other hand, natural buffering might diminish the potentially beneficial increase growth hormone activity.  Overall, on account of the competing antagonistic effects, I doubt that buffering is an important adjunct to training.   The issue is similar to the debate about the value of cold baths to reduce inflammation after training.

Nonetheless, the possibility that buffering might increase tolerance of lactate production, together with the substantial evidence for improved endurance performance in rats and humans, reviewed  McNaughton and colleagues, has led to the proposal that bicarbonate doping might enhance race performance.  I am intrinsically opposed to the ingestion of substances in marked excess of the amounts present in a normal healthy diet for the sake of enhancing performance, but some athletes might argue that provided it is not illegal it is acceptable.   However, the dose required to produce an appreciable effect (20-30 gm) can cause vomiting or diarrhoea.  I would regard this is too great a risk to take.

Long term improvement

It is clear that many of the physiological adaptations required to minimise the rate of accumulation of lactate can be achieved very efficiently by HIIT.  This evidence undermines the principle that enhancement of the ability to handle lactate is achieved most effectively by specific training in the vicinity of LT.

Unfortunately, most of the HIIT research so far has focussed on the contrast of HIIT with lower intensity training, delivered over a time scale of several weeks.   There is some evidence  that the benefits of HIIT do plateau after a period of a few months.   The study by Stoggl and Sperlich demonstrated that for athletes who have a history of regular training, polarised training produces greater benefits than either threshold training or predominantly high intensity training.  It is plausible that the adaptations produced by HIIT can also be achieved, perhaps more gradually but with the potential for steady improvement over a prolonged period, by a polarised program.  Hitherto there have been too few studies that have examined the development of physiological capacities such as aerobic enzymes, delivery of blood to muscle and the transport of lactate, during training programs sustained over a full season or longer.

Injury prevention

Injury is an issue of perennial importance to athletes.  In general, muscle injury is likely if a large force is exerted unexpectedly, or if muscles are fatigued.  Protection against injury is minimised by the strengthening promoted by anabolic hormones on the one hand, or diminished by the breakdown of tissues promoted by sustained elevation of catabolic hormones such as cortisol.  In the next post in this series, I will address the question of whether injury is more or less likely with a polarised program than with threshold training.

Is threshold training over-rated? Stephen Seiler v Jack Daniels

December 19, 2016

In the early years of a runner’s career, almost any reasonably sensible training plan with a gradual build-up of training load will produce improvement.  However, once a runner has reached a plateau of performance, the challenge is to identify the type of training that offers the best chance of further improvement.   Races ranging from 5K to marathon are run at paces in the vicinity of lactate threshold (LT).  Race performance is largely determined by the fact that as pace rises above lactate threshold, acid accumulates in muscles and blood, eventually resulting in an enforced slow-down.  Thus, one of the major goals of training is increasing pace at lactate threshold, as this will allow increased race pace.  The principle of specificity of training suggests that the optimum training program will include a large amount of running near lactate threshold to enhance capacity to prevent accumulation of acid.  Indeed, this is the approach adopted by many recreational runners.

Polarized training

However, the evidence from examination of the training logs of elite endurance athletes, reviewed comprehensively in a lecture by Stephen Seiler in Paris in 2013, indicates that many elites adopt a polarised approach  that places emphasis on the two extremes of intensity. There is a large amount of low intensity training (comfortably below LT) and an appreciable minority of high intensity training (above LT).  Polarised training does also include some training near lactate threshold, but the amount of threshold training is modest; typically the proportions are 80% low intensity, 10% threshold and 10% high intensity.

As reviewed in my previous post on the topic, several scientific comparisons  of training programs have demonstrated that for well-trained athletes who have reached a plateau of performance, polarised training produces greater gains in fitness and performance, than other forms of training such as threshold training on the one hand, or high volume, low intensity training on the other.

The specificity principle

Nonetheless many  coaches and athletes who advocate specific training paces to achieve the various required adaptations required for distance running, maintain a firml belief that threshold training is the best way to increase the pace at lactate threshold, and should form a substantial component of a distance runner’s training program.  Jack Daniels, doyen among coaches advocating specific paces for specific adaptations, has argued that because stress level rises rapidly at paces exceeding threshold there is a sweet spot in the vicinity of lactate threshold that achieves sufficient stress to promote adaptation while avoiding the danger of excessive stress.

Evidence from laboratory studies of rats appears to provide some support for this view.  While it is necessary to be cautious in using evidence from studies of rats to inform training of humans, the basic physiology of rat muscle is similar to that of human muscle.  They share with us an aptitude for running at aerobic paces. The evidence from the well-controlled systematic studies that are feasible in rats is potentially useful in establishing principles that apply across species.  Dudley’s studies in which he measured changes in aerobic enzymes produced by a variety of different training intensities and durations in rats (all training for 5 days per week for 8 weeks) demonstrated that running beyond a certain duration produced no further increase in aerobic enzymes.   Furthermore, the duration of running beyond which there was no further improvement is shorter at higher training intensity.  This suggests that at any given intensity, training runs beyond a certain duration  will produce no further increase in aerobic capacity though there might of course be other gains, for example increase resilience of bones, muscles, ligaments, tendons and also the mind.  But there is also likely to be an increase in overall stress.  At very high intensity the duration limit is so short that the overall gain in aerobic fitness is less than can be achieved by longer session at lower intensity. The greatest overall increase in aerobic enzymes in muscles with predominantly red (aerobic) fibres, was achieved by an intensity that led to maximum gain at around 60 minutes.  Thus in Dudley’s rats, there appeared to be a sweet spot in intensity for optimum development of aerobic capacity.  Although Dudley did not measure lactate levels, it is plausible that this intensity corresponds roughly to lactate threshold in humans.

Hormones and training

However even if we accept that Dudley’s studies support Jack Daniel’s argument for a sweet spot, it is crucial to note that Dudley assessed the effects of training over a total duration of only eight weeks.  The important issue for the athlete who has reached a plateau is the likely consequences of training over a longer time-scale than 8 weeks.  It is probable that the crucial issue is the balance between catabolic and anabolic effects of training.  During a training session, the catabolic hormones cortisol and noradrenaline are released into the blood stream to mobilise body resources, especially glucose, required to meet the demands of training.  The release of catabolic hormones also triggers the subsequent release of anabolic hormones, such as growth hormone, that promote repair and strengthening of body tissues.    As training intensity rises above lactate threshold the release of catabolic hormones and the associated release of anabolic hormones increases sharply (as illustrated by Wahl and colleagues).  Thus the potential stimulus triggering the benefits of training rises sharply as intensity exceeds lactate threshold.  The accumulation of cortisol also increases with increased duration of running.  For example, Cook and colleagues report that salivary cortisol increases steadily during a marathon, typically achieving a fourfold increase at 30 minutes after completion of the race compared with the level prior to the start.

While a transient rise in cortisol tends to be beneficial, sustained elevation of cortisol is potentially harmful because cortisol promotes the breakdown of body tissues.  Cortisol levels in hair samples provide an indication of cortisol level sustained over a period of weeks or months.   Skoluda et al measured cortisol levels in hair in a group of distance runners over a season. They reported that these runners had abnormally high cortisol levels over a prolonged period, raising the possibility of adverse sustained catabolic effects, including suppression of the immune system.  Skoluda concluded that repeated physical stress of intensive training and competitive races is associated with potentially harmful sustained elevation of cortisol.  However, they did not explicitly compare different training programs.

There is no published evidence of differences in medium or long term catabolic/anabolic balance between polarised training and threshold training.  Furthermore, because gradual increase in training load leads to a blunting of the sharp rise in catabolic hormones produced by training in the vicinity of LT, a fully informative study would need to take careful account of the structure of the training program over a sustained period.  Nonetheless a study of high level distance runners by Balsalobre-Fernandez and colleagues does provide relevant information.  They recorded training, performance and salivary cortisol level in 15 high-level middle and long-distance runners from the High Performance Sports Center, Madrid, throughout a period of 10 months.  The group comprised 12 men and 3 women, mean age 26.4 years, with personal bests in 1500-metres between 3:38–3:58 (men) and 4:12–4:23 (women). They rated training in three zones: zone 1 included long-distance continuous training, or interval training with long sets (4–6 km), at relatively relaxed paces; zone 2 included of intervals with sets of 1–3 km at approximately 5 K pace , likely to be moderately above lactate threshold; zone 3 included short-distance and sprint interval training at paces ranging from around 1500m pace to full sprint. Thus zone 1 and 3 roughly correspond to low intensity and high intensity zones of a polarised program, while zone 2 sessions are a little more intense but less sustained than a typical threshold training session in the mid-zone of a typical polarised program.

During the winter months, the athletes did a substantial amount of low intensity (zone 1) training.  The 25 weeks of spring and summer training was dominated by zone 2 training.  For 15 weeks within this 25 week period, the average training zone was in the range 1.75-2.25, indicating a large proportion of zone 2 training; while for 3 weeks the average was above 2.25, indicating an appreciable amount of training in zone 3 in addition to zone 2.

In addition to recording race performance, Balsalobre-Fernandez and colleagues regularly assessed vertical counter-move jump height (CMJ) as a measure of neuromuscular performance.  Averaged over the entire season, the runners with higher long-term cortisol levels has significantly lower CMJ scores, confirming that sustained elevation of cortisol is associated with poor neuromuscular performance.  However, analysis of correlations between weekly average cortisol and CMJ values revealed that higher CMJ scores were recorded in weeks with higher cortisol levels, indicating that transient elevation of cortisol is associated with better neuromuscular performance.  The weeks with higher CMJ performance were weeks with lower training volume but higher training intensity (i.e. more Zone 3 sessions).  Finally, CMJ scores were significantly higher in the week before the season’s best competition performance

In summary, the evidence from the study by Balsalobre-Fernadez and colleagues confirms that sustained elevation of cortisol is harmful and favours a lower volume of higher intensity training rather than moderately large volume a little above lactate threshold.  This might be a key to understanding why polarised training might be superior to threshold training.   In my next post, I will examine the mechanisms by which the training adaptations required for distance running might be best achieved using a polarised approach.  In particular I will discuss the ability of negative ions such as phosphate and bicarbonate in the blood to provide temporary buffering of the acidity associated with lactate production.  This buffering might allow transient surges of lactate produced by brief high intensity exercise to produce beneficial enhancement of the transporter molecules that facilitate transport of lactate from type 2 to type 1 muscle fibres in which it can be used as fuel, and also the transport of lactate from muscles to liver and heart, without the potentially damaging effects of increased acid levels associated with sustained increase in level of lactate.

Hill sprints

December 3, 2016

In recent days there has been an interesting discussion on the Fetcheveryone ‘Polarised training’ thread about the value of the short intense hill sprints that Renato Canova and Brad Hudson recommend for distance runners.

Typically these take to form of 6 or more short (6-8 second) intense uphill sprints with adequate recovery between each sprint.  They can be done at either the beginning or end of a training session.   Canova recommends them up to twice a week. I have never done them more frequently than once per week.   Although 6 hill sprints do not add greatly to the training load of a ‘serious’ athlete, I have always been concerned to avoid the risk of excessive stress.   It is more important to maintain good form that promotes optimum muscle fibre recruitment

One of the immediate benefits is a feeling of speed in your legs that can make subsequent fast pace running feel relatively easy.   Some athletes do intense hill sprints in the 24 hours before a race for this purpose.  Although I have not habitually done this, I usually do  ‘bounding’ drills during the taper for a target race to achieve a similar result.  In fact hill sprints are probably safer than bounding drills as they present little risk of injury provided you warm up adequately.

I think that the feeling of ‘having speed in your legs’ is based largely on the sensation of recruiting fast twitch fibres.  However, you might wonder why this is helpful for a long distance runner, since fast twitch fibres are poorly adapted for aerobic metabolism.  I suspect the reason is that fast twitch fibres are good at capturing the energy of impact at footfall as elastic energy.  Provided you have developed the ability to recycle lactate from fast-twitch fibres to slow twitch fibres that can use the lactate as fuel, the fast twitch contractions do not lead to increase in blood acidity.