Stretching: What’s the big whoop? Debunking one of the oldest exercise myths

Flexibility is a fantastic asset, especially from an athletic point of view. Maintained stretching (15-20 seconds) results in the elongation of muscle through a few mechanisms including stress relaxation and the alignment  of collagen fibres (of the connective tissues) along the line of tension. Having longer muscles allows for a greater range of movement about your joints, which can lead to benefits like increasing the stride length for runners!

flex cell

Muscle fibres consist of bundles of myofibrils, repeating units of the functional unit of the muscle: the sarcomere. The sarcomere consists of chains of actin (thin filaments – blue) and myosin (thick filaments – red). To contract, ATP (which we derive from the sugar in our diet) is utlised to slide these filaments over one another such that they overlap more, shortening the muscle fibres. During stretching, the degree of overlap lessens, lengthening our muscles.

Furthermore, the process of stretching is helpful in the sense that it also facilitates the realignment of disorganised muscles fibres, increases blood flow to the muscle body (allowing for the removal of toxins such as lactate which build up during exercise) and can result in the strengthening of myotendon junctions (where the muscle inserts into the tendon) through the production of microtears which repair during rest and recovery. However, (as you may have heard many times before) stretching your muscles in this manner before exercise can be a bad idea, as a study we came across reveals:

In this piece of work, 10 healthy volunteers with no history of injury to the right ankle were analysed to determine the effect of passive stretching on maximum voluntary contractility and stiffness of the soleus (see diagram below). Half of the subjects undertook a bout of passive stretching which involved 13 maximal stretches (alternating between maximal tolerated plantar flexion and dorsiflexion – demonstrated below) with 5 seconds rest between each, over 33 minutes. Clearly this is far more than any athlete would stretch an individual muscle. The other volunteers acted as a control group by not completing the stretches.

flex graph

Immediately post-stretching (or not stretching in the case of the controls) measurements for maximum voluntary contractility MVC (i.e. strength), muscle activation (measured as the percentage of motor units within the muscle which are successfully recruited during contraction) and muscle stiffness were obtained.

flex GRAPHHH

A) The control group, who did not undergo stretching, are able to produce a significantly higher maximum voluntary contraction than those who did. B) It seems that the process of stretching decreases the degree to which the muscle can be activated during contraction. C) Stretching the soleus significantly decreases its stiffness.

This experiment suggests that by stretching before exercise, the degree to which a muscle can be activated  to contract (i.e. the muscle strength) is decreased and although this value returns to close to 100% by 15 minutes, the maximum voluntary contractility is still reduced by up to 8% after an hour after stretching (down from 25% immediately post-stretching). Stretching incorrectly, therefore, might lead to a decreased ability to perform to your maximum potential during a race. Fatigue plays no part in this effect under these circumstances as the stretching process is passive. However if an athlete were to carry out these stretches individually, fatigue may also contribute to decreased muscle performance.

Muscle stiffness correlates with maximum voluntary contractility and could perhaps account in part for the observed reduction in strength. These data apparently corroborate data collected in a study entitled “Acute muscle stretching inhibits maximal strength performance” though we cannot access this article. Unfortunately, the study I have described only focused on a very limited sample set but the findings are quite interesting. It has at least scared me away from stretching pre-race.

The solution? While stretching is beneficial and does have its place, before a race or workout is not the time to do it. Pre-race, it is recommended to not do any static stretches. Rather, by actively stretching (through dynamic exercises such as high knees and bum kicks) you increase your heart rate, increase your range of muscle movement and increase muscle activation, without weakening your muscles, hopefully resulting in a stronger performance! Limit static stretches to post-exercise while your muscles are still warm, and (as I have been advised) work systematically through your muscles, holding each stretch for 15-20 seconds.

Thanks for reading!

James.

 

If you enjoyed this, you might like our other posts:

Running and circadian rhythms

The molecular basis of creatine

 

Images adapted from:

http://en.wikipedia.org/wiki/File:Sarcomere.svg

http://www.ucl.ac.uk/~sjjgsca/muscleSlidingFilament.html

http://ibexadventure.com/2011/05/solutions-for-a-strained-soleus/

Source:

Fowles JR, Sale DG, & MacDougall JD (2000). Reduced strength after passive stretch of the human plantarflexors. Journal of applied physiology (Bethesda, Md. : 1985), 89 (3), 1179-88 PMID: 10956367

 

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2 responses to “Stretching: What’s the big whoop? Debunking one of the oldest exercise myths

  1. Hello, my name is Ashley Armstrong and I am a first year graduate student in Mechanical Engineering at the University of Illinois. I am publishing a review paper on the musculoskeletal effects of Cerebral Palsy in the journal called Clinical Biomechanics and I currently have one of your figures from this article in my current draft of the paper. I am writing to you to ask for permission to use this image in my final version. I would of course site your website.

    All the best,
    Ashley Armstrong

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