Article Title



Elise Hodges, Ryann Shepherd, Claire Nagel, Kristina Woodford, Rebecca Larson, Hugo Pereira and Christopher Black

University of Oklahoma, Norman, OK

Abstract. Intense or prolonged exercise may lead to fatigue, or an inability to produce a required muscular force. Critical Torque (CT, the isometric equivalent to critical power) is a threshold torque output that can be maintained indefinitely and provides a way to better understand exercise intolerance and muscular fatigue. Electrical stimulation allows for examination of the peripheral components of CT and little is known about the effects of aerobic training status on the recovery of these parameters. PURPOSE. The purpose of this study was to examine how aerobic training status and recovery time (5- or 15-min of rest between bouts) altered CT (determined using two different stimulation frequencies 20 and 100Hz). METHODS. Twenty-six participants (10 trained, peak VO2 values 54.3 ± 6.8 and 16 untrained, peak 38.0 ± 5.6 mL∙kg-1∙/min-1,) completed four bouts of electrically stimulated exercise, consisting of 75 contractions using a 2-sec:2-sec on/off duty cycle of the knee extensors. A rest period of 5 or 15-min between bouts was randomly assigned. Absolute CT was calculated as the mean torque of the final six contractions and relative CT was calculated by normalizing torque to the peak torque during 100 Hz stimulation. RESULTS. Relative CT at 100Hz did not differ between trained or untrained or between rest periods (p ≥0.26). For absolute CT at 100Hz, there was a significant main effect for exercise bout (p=0.003, 18.5 Nm ± 10.2 vs. 16.4 Nm ± 9.3), but no effects for rest period (p=0.40) or training status (p=0.74). Relative CT at 20Hz also did not differ between trained and untrained or between rest periods (p≥0.09), but there was a significant main effect for bout 1 vs bout 2 (p=0.009, 41.6 ± 10% for bout 1 vs. 44.4 ± 14.7% for bout 2). Lastly, there was a significant main effect for absolute CT at 20Hz for exercise bout (p<0.001, 36.6Nm ± 9.3 for bout 1 vs. 29.9Nm ± 7.8 for bout 2), but no significant effects for rest period (p=0.13) or training status (p=0.60). CONCLUSION. Our findings indicate that peripheral fatigue occurred, and unlike in previous studies it did not recover, even when 15-min of rest were provided.

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