Coactivation Does Not Contribute to Fatigue-Induced Decreases in Isokinetic Forearm Flexion and Extension Torque

Abstract

Purpose

The present study examined the effects of a reciprocal, slow velocity forearm flexion and extension task on fatigue-induced changes in isokinetic torque, agonist and antagonist muscle activation, and coactivation ratios at slow and moderate velocities.

Methods

Nine women (mean ± SD: age = 21.0 ± 1.7 years; body mass = 68.1 ± 8.2 kg; height = 167.4 ± 7.2 cm) completed pre-testing for forearm flexion and extension isokinetic peak torque at 60 and 180°/s, a fatiguing task of 50 maximal, reciprocal, isokinetic muscle actions at 60°/s, and post-testing. The amplitude (AMP) of the electromyographic (EMG) signals from the biceps and triceps were simultaneously recorded. Torque and EMG AMP were normalized to the corresponding values from the pre-testing peak torque movements. Repeated measures ANOVAs and pairwise comparisons were used to identify mean changes in torque, EMG AMP, and coactivation ratios.

Results

The torque analyses indicated significant decreases from pre- to post-testing for forearm flexion (14.1% ± 5.0%; P < 0.001) and extension (25.4% ± 12.2%; P < 0.001) at 60°. At 180°/s there was a significant decrease, collapsed across the forearm movements (24.7% ± 11.7%; P < 0.001). For EMG AMP and coactivation ratios, there were no changes (P > 0.05) from pre- to post-testing for either velocity or movement.

Conclusions

The torque responses were velocity-specific, with greater fatigability exhibited for forearm extension versus flexion at 60°/s, but no differences at 180°/s. The parallel EMG AMP responses between the agonist and antagonist muscles for both velocities supported the lack of fatigue-induced changes in coactivation ratios. Thus, our results demonstrated that fatigue-induced decreases in torque were not attributable to increases in antagonist activation or coactivation.