Effects Of Maximal, Reciprocal, Isokinetic Fatigue On Coactivation For Forearm Flexion And Extension

Abstract

PURPOSE: It has been suggested that fatigue-induced decreases in torque may be influenced by coactivation of the antagonist muscle. Previously, studies have examined coactivation in response to single movement fatiguing tasks. Thus, the purpose of the present study was to examine the effects of reciprocal fatigue on activation of the agonist and antagonist muscles. METHODS: Ten women (mean ± SD: age = 21 ± 1.6 years; body mass = 68.8 ± 8.0 kg; height = 169.1 ± 7.3) performed 50 consecutive, maximal, reciprocal, isokinetic muscle actions of the right forearm flexors and extensors at 60 and 180°·s-1. The amplitude (AMP) contents of the electromyographic (EMG) signals from the biceps and triceps were recorded simultaneously throughout the fatiguing task. The average of the first 5 (Initial) and last 5 (Final) repetitions were used for analyses. The EMG AMP and torque values were normalized to the pre-test peak torque trials of the same speed. A 2 (Time) x 2 (Speed) x 2 (Muscle) x 2 (Movement) RMANOVA was used to determine mean differences for EMG AMP. A 2 (Time) x 2 (Speed) x 2 (Movement) RMANOVA was used to analyze torque changes across the fatiguing task. Follow-up pairwise comparisons were used when necessary. Paired t-tests were performed to analyze changes in the antagonist/agonist activation ratio from Initial to Final. RESULTS: The torque analyses indicated a significant main effect for Time, collapsed across Speed and Muscle, where Initial (95.8 ± 11.6) was greater than Final (58.1 ± 12.1; p < 0.001). For EMG AMP there was a significant 4-way interaction. Follow-up analyses indicated EMG AMP increased significantly from Initial to Final during flexion of the biceps (102.8 ± 29.6 to 157.8 ± 52.1) and triceps (18 ± 8.8 to 23.8 ± 9.6), and during extension of the triceps (107 ± 16.5 to 144 ± 22.2) and biceps (16.2 ± 8.1 to 22.6 ± 9) at 180°·s-1, while there was no change (p > 0.05) in either muscle, during either movement at 60°·s-1. There were no significant differences (p > 0.05) in the antagonist/agonist ratios at either speed during flexion or extension. CONCLUSION: The results of the study indicated a speed specific activation response to fatigue. There was a similar magnitude of increase in activation among the agonist and antagonist muscles, suggesting the decrease in torque with fatigue was not influenced by coactivation.