Velocity-Specific Coactivation and Neuromuscular Responses to Fatiguing, Reciprocal, Isokinetic, Forearm Flexion, and Extension Muscle Actions

Abstract

Neltner, TJ, Anders, JPV, Keller, JL, Smith, RW, Housh, TJ, Schmidt, RJ, and Johnson, GO. Velocity-specific coactivation and neuromuscular responses to fatiguing, reciprocal, isokinetic, forearm flexion, and extension muscle actions. J Strength Cond Res 36(3): 649-660, 2022-The purpose of this study was to examine the effects of fatiguing, reciprocal, maximal, isokinetic, forearm flexion, and extension on coactivation. Ten recreationally trained women (mean 6 SD: age 5 21 6 1.63 years) performed 50 maximal, reciprocal, isokinetic, forearm flexion, and extension muscle actions at 60 and 180˚•s 21 on separate days. Electromyographic (EMG) and mechanomyographic (MMG) signals from the biceps brachii (BB) and triceps brachii (TB) were recorded. A 2 (time) 3 2 (velocity) 3 2 (movement) and 4 separate 2 (time) 3 2 (velocity) 3 2 (muscle) 3 2 (movement) repeated-measures analysis of variances were used to examine normalized torque and normalized EMG and MMG amplitude (AMP) and mean power frequency, respectively, with an alpha of p , 0.05. There were no significant interactions for torque but a main effect for time (p , 0.001, d 5 3.29) such that it decreased. There was a significant four-way interaction for EMG AMP (p 5 0.004, h 2 p 5 0.61) which revealed parallel responses between the BB and TB during both movements, with no changes at 60˚•s 21 and increases at 180˚•s 21 . The current findings suggested a common drive between agonist and antagonist muscles during fatiguing forearm flexion and extension muscle actions, with velocity-specific activation strategies. In addition, both EMG and MMG are viable techniques for assessing coactivation during fatiguing exercise.

Load-Specific Performance Fatigability, Coactivation, and Neuromuscular Responses to Fatiguing Forearm Flexion Muscle Actions in Women

“…The results of the EMG AMP analysis for the BB vs. TB indicated fatigue-induced, load-dependent, changes in the coactivation ratio from the initial to final repetitions, but not from the prefatigue and postfatigue MVIC trials. These findings were consistent with previous studies involving submaximal forearm flexion muscle actions which reported no changes in the coactivation ratio before and after the fatiguing task (23,30,35,37). However, during the RTF at 30% 1RM, there was a significant increase in the coactivation ratio (less coactivation) from the initial to final repetitions, which reflected a 42% increase (from 37 to 79%) in EMG AMP of the agonist BB and a 6% increase (collapsed across 30 and 80% 1RM) in EMG AMP of the TB which functioned as the antagonist.…”

“…Thus, despite performance fatigability being greater in the low- vs. high-load condition, the fatigue-induced reductions in force in this study were less than those previously reported for DCER leg extensions in men (32). The force reductions at the low-load, but not the high-load, in this study were, however, similar to those previously reported for isokinetic forearm flexion in women (35). Perhaps the lower magnitude of fatigability in this study, compared with those previous reported for leg extensions in men, can be attributed to differences in sex-specific fatigue characteristics (22).…”

“…In this study, the magnitude of excitation of the TB when acting as the antagonist was 9–16% of the pretest maximal EMG AMP value when the TB was acting as the agonist. Similar magnitudes of antagonist excitation (8–38%) have been reported for the TB during forearm flexion muscle actions (3,28,35). The results of the EMG AMP analysis for the BB vs. TB indicated fatigue-induced, load-dependent, changes in the coactivation ratio from the initial to final repetitions, but not from the prefatigue and postfatigue MVIC trials.…”

“…Contrary to our findings, in a sample of resistance trained men, Marshall et al (32) reported parallel declines in maximal torque of 76 and 67% after high (80% 1RM) and low (50% 1RM) load DCER leg extensions, respectively. More recently, Neltner et al (35) demonstrated parallel decreases in intraset forearm flexion torque development ranging from 32 to 38% during 50 maximal, reciprocal, isokinetic forearm flexion, and extension muscle actions at 2 distinct velocities. Thus, despite performance fatigability being greater in the low-vs. highload condition, the fatigue-induced reductions in force in this study were less than those previously reported for DCER leg extensions in men (32).…”