Jocelyn E. Arnett^1,, Robert W. Smith¹, Tyler J. Neltner¹, John Paul V. Anders², Dolores G. Ortega¹, Terry J. Housh¹, Richard J. Schmidt¹, Glen O. Johnson¹

The purpose of this study was to compare the composite, inter-individual, and intra-individual differences in the fatigue-induced torque, electromyographic (EMG), and mechanomyographic (MMG) patterns of responses during sustained, isometric fatiguing tasks anchored to a rating of perceived exertion (RPE) at elbow joint angles (JA) of 75° and 125°. Nine women (age: 21.0±3.0 yrs; height: 169.3±8.1 cm; body mass: 68.4±7.4 kg) performed 2,3s forearm flexion maximal voluntary isometric contractions (MVIC) before and after sustained, isometric forearm flexion tasks anchored to RPE = 8 to task failure (defined as torque reduced to zero) at JA75 and JA125. The EMG and MMG signals were recorded from the biceps brachii (BB). Polynomial regression analyses (linear and quadratic) were performed to examine the patterns for the torque, neuromuscular responses, and neuromuscular efficiency (NME) vs. time relationships. Six, separate 2 (Joint Angle: 75° vs 125°) x 2 (Time: Initial vs 5%TTF) repeated measures ANOVAs were performed to assess the mean differences for the torque and neuromuscular parameters values between the initial value and the value at 5%TTF. At JA75, there were significant (p≤0.05) negative torque (quadratic), EMG amplitude (AMP) (linear), EMG mean power frequency (MPF) (quadratic), MMG MPF (linear), and NME (linear) vs. time relationships. At JA125, there were significant (p≤0.05) negative torque (quadratic), EMG AMP (quadratic), EMG MPF (linear), MMG MPF (linear), and NME (linear) vs. time relationships. MMG AMP, however, did not change across time (p≥0.05) at JA75 or JA125. The individual neuromuscular responses varied from the composite data within and between JA75 and JA125. These findings indicated that for torque, joint angle did not affect the composite and individual responses when anchored to RPE = 8. There was, however, substantial inter- and intra-individual variability in the neuromuscular responses that may be specific to the joint angle at which the tasks were performed.

female, ratings of perceived exertion, fatigue, electromyography, mechanomyography, forearm flexion, neuromuscular