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unknown user
12-10-1999, 01:08 PM
Hello all,

I would like to add some additional thoughts to Dr. van den Bogert's and
Dr. Devita's comments on this interesting topic.

3) Along the lines of inhibition during isokinetic testing. Dr. Graham Caldwell
and I have compared the EMG and kinematics of sprinters running on a treadmill
at 30% grade and 4.5 m/s to running at the same stride frequency as the incline
(MSSE in press). We found EMG amplitudes over 400% MVC in the mono-articular
hip extensors, knee extensors, and plantar flexors as well as in the bi-articular
rectus femoris and gastrocnemius during the stance phase of the incline condition
and amplitudes of over 200% MVC (as did Jacobs and van Ingen Schenau) during
level running at ~7.6 m/s (same stride frequency). I agree that there are
some methodological problems with EMG amplitude/MVC measures, but these amplitudes
are so much higher that there still may be something to "lazy" motor control.


4) Energy transfer mechanisms via bi-articular muscles. Jacobs et al. (J.
Biomech. 29(4): 513-523, 1996) and Prilutsky and Zatsiorsky (J. Biomech.
27(1): 25-34, 1994) have shown/suggested that energy generated at adjacent
joints can be transferred via bi-articular muscles to assist in torque production
at the joint of interest--such as the rectus femoris may do when the hip
and knee are extending concomitantly during dynamic leg extension activities
(vertical jumps, running, sprint push-offs). Adjacent joints are typically
fixed during iso-kinetic testing.

5) Differing muscle lengths of bi-articular muscles. This is especially
evident with the hamstrings during isokinetic testing of the knee. Altering
hip angles has a large effect on isokinetic knee flexor torque (Johnson et
al. MSSE 30(5s): abstract #267, p. s47, 1998) most likely due to the hamstrings
operating on different portions of the length/tension curve. Standardization
of adjacent joint angles during isokinetic testing has sometimes been lacking.


I look forward to continued discussion on this interesting topic.

Regards,


Steve

Stephen C. Swanson, MS
Biomechanist
Institute for Sport Science and Medicine at
The Orthopedic Specialty Hospital
5848 South Fashion Blvd.
Salt Lake City, UT 84107

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