Muscle activation and time to task failure differ with load type and contraction intensity for a human hand muscle |
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Authors: | Email author" target="_blank">Katrina?S?MalufEmail author Minoru?Shinohara Jennifer?L?Stephenson Roger?M?Enoka |
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Institution: | (1) Department of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA |
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Abstract: | Time to failure for sustained isometric contractions of the elbow flexors is briefer when maintaining a constant elbow angle
while supporting an inertial load (position task) compared with exerting an equivalent torque against a rigid restraint (force
task). Our primary purpose was to determine whether the effects of load type on time to task failure exist when motor unit
recruitment cannot be enhanced during a sustained submaximal contraction of an intrinsic hand muscle. A second purpose was
to determine whether a greater reserve remains in the muscle after early failure of the position task. Two groups of 10 strength-matched
men performed the force and position tasks at either 20% or 60% of maximal force (MVC) with the first dorsal interosseus,
followed by a second force task at the same relative intensity. The rate of increase in surface EMG was greater (P = 0.002) and time to failure was briefer (P = 0.005) for the position task (593±212 s) compared with the force task (983±328 s) at 20% MVC, whereas there were no task
differences in these variables at 60% MVC (P ≥ 0.200). Time to failure for the second force tasks did not differ at either contraction intensity (P≥0.743). These results demonstrate that previously observed effects of load type generalize to a hand muscle, although only
for low-intensity contractions. For the position task at low forces, muscle activity increased more rapidly and no additional
reserve remained in the muscle at failure compared with the force task. We propose that the briefer time to failure for the
position task during sustained, low-intensity contractions is due to earlier recruitment of the motor unit pool. |
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Keywords: | Muscle fatigue Electromyography Isometric contraction |
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