Hello,
I am a physical therapist with not much training in formal biomechanics
or EMG stuff. In reading this post aabout correct muscle action it seems
that it indicates that there is an improvement in the "core stability" of
the lifters within their training session. Does not the decrease in
external sway... indicate an increase in the central postural control/
proprioceptive response system? Would'nt the variation in the EMG
activity of the trained lifters indicate the rapidly changing muscle
activity that would be required to maintain a more precise trajectory? If
my thinking is along the correct lines I do not see why this is the
opposite of what would be expected if the "correct muscle recruitment"
hypothesis were to be believed. Does this mean that if the correct muscle
recruitment hypothesis was correct that there would be less EMG activity
as well as less sway/smoother trajectory of the lift? My understanding of
core stability is that it is a pattern of muscle recruitment that improves
stability centrally that allows a more precise movement distally. It is
not meant to produce a rigidity which would seem to make precision more
difficult. Trunk stability is a concept that therapist that work with the
neurologically involved population have used for years on an intuitive
basis I guess.
Thanks for reading this jumbled message,
Glenn
On Fri, 5 Jan 2001 [log in to unmask] wrote:
> 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
> [log in to unmask]
>
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