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1 Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON, Canada
2 Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON, Canada; Department of Anatomy and Cell Biology, Faculty of Medicine and Dentistry, The University of Western Ontario, London, ON, Canada
* To whom correspondence should be addressed. E-mail: crice{at}uwo.ca.
The purpose of this study was to compare fatigue and recovery of maximal voluntary torque (MVC) and muscle oxygenation following voluntary (VOL) and electrically stimulated (ES) protocols of equal work. On one day, ten male subjects (25 ± 4y) completed a VOL fatigue protocol and, on a separate day, an ES fatigue protocol of the right dorsiflexors. Each task involved 2 min of intermittent (2-s on, 1-s off) isometric contractions at 50% of MVC. For the ES protocol, stimulation was delivered percutaneously to the common peroneal nerve at a frequency of 25 Hz. Compared with the VOL protocol, the ES protocol caused a greater impairment in MVC (75% vs. 83% pre-fatigue value; PRE) and greater increase in 50Hz half-relaxation time (165% vs. 117% PRE) post-exercise. Following acute (1 min) recovery, MVC impairment was similar for both protocols, whereas 50Hz half-relaxation time was still greater in the ES than VOL protocol. Total hemoglobin decreased to a similar extent in both protocols during exercise, but was elevated above the resting value to a significantly greater extent for the ES protocol in recovery (18 µM vs. 11 µM). Oxygen saturation was significantly lower in the ES than VOL protocol during exercise (46% vs. 57% PRE), but significantly greater during recovery (120% vs. 105% PRE). These findings suggest that in spite of equal work, ES contractions impose a greater metabolic demand on the muscle that leads to a transient greater impairment in MVC. The enforced synchronization and fixed frequency of excitation inherent to ES are the most likely causes for the exacerbated changes in the ES compared with the VOL protocol.
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