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The muscular system is
controlled by the nervous system. Muscles have no control of their own.
The obvious conclusion to draw is that people get tight muscles because
their nervous system is stimulating them to contract, generally through
learned habit. To be muscle-bound is to have muscles constantly triggered
to shorten by the nervous system.
That being the case, how can someone being stretched by
someone else possibly improve their control of their own muscle-tension?
To do so requires learning self-control, which is not the point when
someone else is stretching you - or even when you are stretching
yourself. The changes that result from stretching are therefore generally
unpredictable and unstable - as evident by the frequency of sports
injuries involving hamstrings.
As a result, people return, by tendency, to the level of
tension (and shortening) they experience habitually.
Athletes and dancers attempt to stretch their hamstrings
to avoid injury. "Attempt" is the correct word because stretching produces
only limited and temporary effects, which is one reason why so many
athletes (and dancers) suffer pulled hamstrings and knee problems.
Clearly, whatever benefits stretching confers, it has
some significant limitations. More than that, stretching has drawbacks -
and the pun is apt.
As anyone who has had someone stretch their hamstrings
for them knows, forcible stretching is usually a painful ordeal. In
addition, stretching the hamstrings disrupts their natural coordination
with the quadriceps muscles, which is why ones legs feel shaky after
stretching the hamstrings. The same is true of stretching any other
muscle. More than that, because muscular tension is maintained as a habit
(by which we maintain our sense of "normal" tension and posture) that is
protected by a postural reflex (the stretch reflex or "myotatic" reflex),
forceful stretching provokes that reflex to assert itself even more
strongly; the increased muscular tension makes repeated stretching
necessary. If one stretches themselves by pitting one muscle group against
another (which is what people usually do), the tension of both muscle
groups may increase -- a condition referred to as co-contraction.
Fortunately, there is a more effective way to manage
muscular tension than by stretching.
To lay the groundwork for your understanding of this
other way of getting muscles to lengthen, it is helpful for me to explain
why stretching works to the degree that it does.
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