Currently there is a great deal of discussion of the "correct" posture and
pattern of moving or lifting, but there are at least two processes involved:
1. The 'correctness', precision, repeatability of the external movement of
the body
2. The 'correctness', precision, repeatability of the internal muscle
involvement
Most of the discussion of core stabilisation, transversus abdominis
recruitment and rotator cuff action suggests that both of the above processes
take place in a very deterministic manner. Thus, it is implied that the
pattern of external posture or movement is "correct" if the pattern of
internal muscle involvement is "correct". Moreover, this also implies that
the same pattern of muscle action always produces the same output motor
pattern and any other pattern of muscle action cannot do so.
This functional relationship, however, has not been confirmed to be correct,
yet it is assumed so often that many folk seem to accept that it is virtually
a law. Several studies involving simultaneous video recording of the
external movement and EMGs of given muscles has shown that this assumption is
far form the truth.
For example, the Russian scientist Pakhamov analysed the variation in muscle
EMGs during the Olympic lifts and found that the least variation took place
in the external movement, but there was significant variation in the EMG
indicators (Zhekov IP "'Biomechanics of the Weightlifting Exercises', 1976).
Interestingly, the variation of all the functional indicators decreases with
increase in load on the bar, but was much wider with light loads or no loads
at all.
During a prolonged training session, the degree of variation changed. With
novices and lower qualified lifters, the variation decreased during the
middle of the session, but rose towards the end. In highly qualified
lifters, it was very interesting to discover that, as the variation in the
trajectory of the bar decreased, the variation in EMG increased, which is
precisely the opposite of what would be expected if the ideas of the "correct
muscle recruitment" hypothesis are to be believed.
As Zhekov noted, this corroborates Bernstein's hypothesis that, in the
repeated reproduction of a movement, one observes a "repetition without
repetition". Apparently, the variation is a general characteristic of
programmed movement which allows one to create and store different motor
programs and to select the optimal movement variant in a given situation.
This variational principle, according to Pakhomov, provides a large
reliability to enable the athlete to produce the required movement.
Furthermore, this switching between controlling and muscle groups serves to
delay the onset of fatigue and minimises any increase in injury risk.
Dr Mel C Siff
Denver, USA
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