Science and Stretching Mechanisms

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One thing that makes writing these articles difficult is that it’s hard to state anything scientific in clear and certain terms.  Take any given subject…stretching for instance. There are still so many questions about things that seem so basic; should you stretch before you engage in a vigorous physical activity?  Is ballistic stretching (bouncy stretching)  good or damaging? Does stretching do you any good at all?  New research and new theories are still being published that inform these questions.


For instance, there was a 2010 meta analysis of several experiments (they were randomized control trials, which is a way to structure an experiment and is considered good research) on the observed effects of stretching.  The basic question was, “What does stretching do?” or “By what mechanism does it create an effect?”.


It’s been believed for a long time that the primary effect of stretching was an increase in the length of our tissue – either by slowly adding extra tissue, or by making the tissue that’s there more elastic, or possibly by using a reflex effect that tells muscles to contract less.  What this study showed was that none of those effects was significant. If extra muscle bits (sarcomeres) were added then there was a corresponding shortening of all the bits to accommodate the new ones. And if the muscle was stretched the tensile load travelling through the muscle didn’t decrease over time.  


Instead the reason why we seem to be able to move our body part into positions that were more difficult before the stretch is because the act of stretching modified the sensations of the limb being in that position.  In other words, it’s not that your hamstrings tissues got longer after you stretched them, it’s that your mind (nervous system, biofeedback mechanism…what have you) found the sensations more acceptable and allowed more movement to take place.  


Now…I’m going out on my own limb and away from the pure, cautious tones of good science…the way I think of that is the body saying something like. “Whoa! What’re you doing with my hamstrings!?  Hang on just a minute!” and so you wait for a minute and then the body says, “Hmmph! Well…I guess that’s okay…go ahead then.”

You’d get laughed right out of your lab coat if you said something like that in a science article.


But let’s celebrate for a minute how truly cool this little grain of evidence is.  Think of all the times you were stretching your hamstrings or what have you, picturing in your mind’s-eye the rubber bands of tissue getting elongated, when in reality you may have been recalibrating your biofeedback loop to allow you to move farther into a range of motion without alarm bells going off.


Now just what the implications are for Davis’ Law of soft-tissue modeling, we’ll have to wait and see.

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