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It is often fashionable
to attribute poor performance or sports injuries very glibly to "muscle
imbalance", which is a result of one's regular training or sport leading to
one muscle group being stronger or weaker than another. Sometimes, this
imbalance is quantified by use of an isokinetic dynamometer, by "manual
testing" or on the basis of differences between the isolated actions of
"agonist" and "antagonist" muscles.
Despite the fact that substantial differences in strength or joint torque
between opposing limbs have not categorically been shown to correlate with an
increase in the incidence of injury, this very general notion of "muscle
balance" often seems to be applied in a very simplistic manner to address
the alleged problem. This diagnosis then guides the therapist or trainer to draw
up a list of suitable exercises to increase the strength of the apparently
offending muscles. But is this approach necessarily logical and appropriate?
Since strength is a function of musculoskeletal structure and function, any
alleged imbalance may be modified by improving the structure or the function, or
both, of these features. This is where a therapeutic dilemma arises. Is the
"imbalance" due to some sort of deficit in intrinsic strength of the
muscle itself or is due to inefficient activation or motor control of the
muscles involved in the action? After all, what may be considered as a deficit
in muscle hypertrophy or intrinsic strength may really reflect some deficit in
neuromuscular control, so that a more appropriate solution would be to improve
the motor skills in specific movement patterns.
Part of the problem may even be related to the unwanted intervention of
inhibitory processes which limit one's ability to produce maximal strength (or
joint torque) in a given action, something which occurs quire reflexively in
many muscle groups to prevent further trauma. For example, it is well known that
damage to the knee joint commonly causes reflex inhibition of the knee extensor
muscles, so that measuring the strength of muscles where some small injury or
overtraining is present may be futile. The muscles involved may be in
"ideal" balance and very strong, but inhibition associated with some
other injury or fear of injury will distort any tests which purport to assess
relative muscle strength.
It might even be that a certain combination of structural and functional
approaches, a mix of enhancing both hypertrophic and neuromuscular types of
therapy would offer the best way of addressing the "imbalance".
In short, is the concept of "muscle balance" being far too
simplistically and liberally applied? If so, what suggestions would you make to
rectify this flawed approach to the management of the given problem?
Dr Mel C Siff
Denver, USA
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