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The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 2030-2039
Copyright ©2000 by the American Physiological Society
Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder, Colorado 80309-0354
Graves, Andrew E.,
Kurt W. Kornatz, and
Roger M. Enoka.
Older Adults Use a Unique Strategy to Lift Inertial Loads With
the Elbow Flexor Muscles. J. Neurophysiol. 83: 2030-2039, 2000. The purpose of this study was to
determine the effect of age on the ability to exert steady forces and
to perform steady flexion movements with the muscles that cross the
elbow joint. An isometric task required subjects to exert a steady
force to match a target force that was displayed on a monitor. An
anisometric task required subjects to raise and lower inertial loads so
that the angular displacement around the elbow joint matched a template
displayed on a monitor. Steadiness was measured as the coefficient of
variation of force and as the normalized standard deviation of wrist
acceleration. For the isometric task, steadiness as a function of
target force decreased similarly for old adults and
young adults. For the anisometric task, steadiness
increased as a function of the inertial load and there
were significant differences caused by age. Old adults were less steady
than young adults during both shortening and lengthening contractions
with the lightest loads. Furthermore, old adults were least steady when
performing lengthening contractions. These behaviors appear to be
associated with the patterns of muscle activation. These results
suggest that different neural strategies are used to control isometric
and anisometric contractions performed with the elbow flexor muscles
and that these strategies do not change in parallel with advancing age.
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