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1 Department of Integrative Physiology, University of Colorado, Boulder, Colorado, United States
* To whom correspondence should be addressed. E-mail: thorsten.rudroff{at}colorado.edu.
Time to failure and EMG activity were measured during two types of sustained submaximal contractions with the elbow flexors that required each subject to exert the same net muscle torque with the forearm in two different postures. Twenty men performed the tasks either by maintaining a constant force while pushing against a force transducer (force task) or by supporting an equivalent load while maintaining a constant elbow angle (position task). The time to failure for the position task with the elbow flexed at 1.57 rad and the forearm horizontal was less than that for the force task (5.2 ± 2.6 and 8.8 ± 3.6 min, P = 0.003), whereas it was similar when the forearm was vertical (7.9 ± 4.1 and 7.8 ± 4.5 min, P = 0.995). The activity of the rotator cuff muscles was greater during the position tasks (25.1 ± 10.1 % MVC) compared with the force tasks (15.2 ± 5.4 % MVC, P < 0.001) in both forearm postures. However, the rates of increase in EMG of the accessory muscles and mean arterial pressure were greater for the position task only when the forearm was horizontal (P < 0.05), whereas it was similar for the elbow flexors. These findings indicate that forearm posture influences the difference in the time to failure for the two fatiguing contractions. When there was a difference between the two tasks, the task with the briefer time to failure involved greater rates of increase in accessory muscle activity and mean arterial pressure.
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