Polarized Training and Injury Prevention

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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10 Responses to “Polarized Training and Injury Prevention”

  1. russtyd Says:

    A recent study in the British Journal of Sports Medicine divided runners into groups based on their foot type and the amount they pronated. The study participants were new to running and were all given the same model of lightweight neutral running shoe instead of a motion-control shoe designed to correct pronation problems. Their mileage and injury rates were tracked for one year. Contrary to what conventional running wisdom might predict, those who overpronated or underpronated were not significantly more likely to get injured compared to runners with neutral foot motion. This study confirms what several other studies have shown.

  2. russtyd Says:

    in fact the pronators had lower injury rates.. http://bjsm.bmj.com/content/early/2016/01/08/bjsports-2015-095031.full

  3. russtyd Says:

    i seem to remember coming across a review noting a study that showed that you could mix up shoe types with foot types and not make any difference to the injury profile.

  4. russtyd Says:

    having attempted a run while fatigued and turning my ankle i appreciate the reminder about collagen fibers! as always thankyou for writing.

  5. canute1 Says:

    Russtyd
    Thanks for your comments, and in particular, thanks for the link to the BJSM article by Malisoux and colleagues.

    That takes the story one step further than the article by Willems that I had referenced. Willems showed that over-pronation at initial assessment was associated with risk of subsequent injury. The BJSM study shows that among those who exhibited pronation, those who wore motion control shoes had lower rates of injury those who who wore standard shoes. Furthermore, those who had pronated feet and wore standard shoes had higher injury rate than those with neutral feet. Thus the evidence in favour of motion control shoes for those with pronated feet is becoming quite strong.

    ,
    However as your subsequent comment indicates, the overall evidence for the benefit of any partcualr shoe type has hitherto been mixed

  6. Ninky Says:

    Enjoyable read as ever canute.

    My own experience suggests running injury rates are influenced most by the following factors.

    Training frequency – inadequate Recovery
    Weight – normally excess but more rarely underweight
    Flexibility – hypermobility causing overstressed of joints, also stiffness/reduction of flexibility as a predictor of injury (perhaps cortisol induced)
    Training intensity – as you describe in your article. Either acute injury from supramaximal efforts or cases of general runs too fast.

    Are you aware of any studies monitoring cortisol levels to injury rates?

    • canute1 Says:

      Ninky, thanks for your comment.

      I do not know of studies showing relating cortisol levels to running injuries, though there are many anecdotal reports of cortisol injections causing tissue damage such as tendon rupture. Abnormal increases on systemic cortisol levels damage body tissues (eg Cushings syndrome, due to excess cortisol, causes visible wasting of muscles) and even a cortisol increase within the normal range is associated with breakdown of proteins in the body https://www.ncbi.nlm.nih.gov/pmc/articles/PMC425032/

      It is chronic cortisol elevation that is does the damage. Balslobre-Fendandez found that high cortisol averaged over the running season was associated with decreased jump height, whereas acute increases in cortisol were associated with increased performance. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4143373/

  7. Ewen Says:

    Thanks again Canute, and all the best for 2017.
    For myself (the experiment of one), relatively higher mileage tends to correlate with fewer injuries. I suspect because of the “resilience building” that you mention that occurs during the steady running days. I’m also careful to vary surfaces, include hills and alternate shoes. That being said, “high mileage” for me only ever topped out at around 70 miles per week.

    On the point of interval training offering some injury prevention results, one thing that faster running does (or helps do) is reduce overstriding. It’s difficult to run fast efficiently when “reaching out with the lower leg” and overstriding. Heel striking or touching with the heel first doesn’t mean the runner is overstriding. They can still have their foot under their centre of gravity on touch down and contact the ground lightly with the heel. Perhaps a small amount of fast running in a weekly schedule is better for injury prevention than regular hard effort interval training and the associated risk of pulled muscles etc?

    • canute1 Says:

      Ewen, Thanks for your comment. Yes I think for most runners a small amount of high intensity running is less likely to cause injury than a large amount of threshold running; in general, for a person in whom speed tends to precipitate injury, short hills are a good option, but as you previously pointed out, hill sprints are a bit risky for someone with a recent calf injury
      I hope your calf niggles are now behind you and that 2017 is a great year for you.

  8. Threshold training: integrating mind and body | Canute's Efficient Running Site Says:

    […] « Polarized Training and Injury Prevention […]

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