Robert W. Smith^1,, Terry J. Housh¹, John Paul V. Anders², Tyler J. Neltner¹, Jocelyn E. Arnett¹, Dolores G. Ortega¹, Richard J. Schmidt¹, Glen O. Johnson¹

Few studies have assessed changes in the time course of the torque and neuromuscular responses during a sustained, isometric task anchored to a constant rating of perceived exertion. The purpose of the present study was to examine the effects of joint angle on the torque and neuromuscular responses during sustained, isometric forearm flexion tasks anchored to RPE = 7 (OMNI-RES scale). Ten college-aged (mean ± SD: age = 21.3 ± 1.8 yrs.) men agreed to participate in this cross-sectional study and performed two, 3s maximal voluntary isometric contractions (MVIC) at elbow joint angles of 75° and 125° before sustained, isometric, forearm flexions anchored to RPE = 7 to task failure at the respective joint angles. The amplitude (AMP) and frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals from the biceps brachii were recorded. Repeated measures ANOVAs and Bonferroni corrected dependent t-tests were used to examine differences across time and between joint angles for torque and neuromuscular parameters. There were decreases (p < 0.05) in torque and EMG AMP across time that were not joint angle dependent, but, there were no changes (p > 0.05) for the other neuromuscular parameters. The results indicated three distinct phases for the torque versus time relationships for both joint angles, including 1) An initial rapid decrease in torque; 2) followed by a plateau; and 3) a final decline in torque to task failure. From these responses, we hypothesized that afferent feedback from group III/IV motor neurons and corollary discharge caused decreases in torque to maintain the prescribed RPE.

perception, exertion, fatigue, torque, electromyography, mechanomyography