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Robert Newton
07-29-1992, 06:48 AM
Dear Biomch-L users,

The development of muscular power in humans has generally centred
around training the stretch shortening cycle capability of the neuromuscular
unit through activities generally termed "plyometrics". Bosco, Komi, Schmidt-
bleicher and others have done some excellent work on the contribution of the
stretch shortening cycle to explosive performance. I would be interested in
any comments or work done on the accelerative concentric contraction of the
muscle and how this can be potentiated with training.

We have developed a device which allows a subject to actually jump off
the ground with a loaded bar and the eccentric landing can be controlled by a
braking mechanism. Similarly, in a bench press type movement, a loaded bar can
be thrown from the chest using an acceleration throughout the movement
achieving peak velocity at or near the end of the range. Previous attempts to
train explosively using traditional weights has been hampered by the fact that
the subject must slow down well before the end of the range where as in most
athletic situations this is the point of maximum velocity. This may explain
why this type of training has not been shown to effectively increase muscle
power output.

I am proposing to complete a training study involving bench throws.
One group will train using counter movement throws from the chest. The second
group will throw the bar but it will be returned slowly to them for the next
throw thus eliminating the eccentric component preventing them from utilising
the stretch shortening cycle. Each group will also be divided into subgroups
based on training load i.e. 10%, 30% and 90% of 1 repetition maximum.

Pre and post testing will involve measurement of maximum power output
during both counter movement and static bench throws, basketball and medicine
ball chest passes into a vertically mounted forceplate to measure impulse of
impact, emg during both throws and stiffness of the musculo-tendinous system
in the bench press position.

It is hoped that such a paradigm will seperate out what proportion of
enhanced power output is due to increased storage of elastic energy,
potentiation of the concentric muscle contraction through activation of the
stretch reflex and the enhanced ability of the muscle to contract
concentrically during high acceleration.

It is theorised that some of the increases in power output with
training are due to an increased ability of the muscle to continue to generate
force at the high velocities experienced during the later part of the movement
during say a throw or a jump i.e. a shift in the force velocity curve towards
greater force production at the higher contraction velocities.

I thank you for your time in reading this message and would greatly
appreciate any comments or suggested references.

Yours sincerely,

-- Robert Newton Internet: rnewton@loki.une.oz.au
Lecturer in Biomechanics ACSnet: rnewton@loki.une.oz
University of NewEngland,
Northern Rivers
P.O. Box 157
Lismore, NSW 2480 AUSTRALIA
Phone: +61 (066) 203762
Fax: +61 (66) 203880