Coactivation During Fatiguing, Maximal, Reciprocal, Isokinetic Forearm Flexion And Extension Muscle Actions Using Mechanomyography

Abstract

Purpose: Mechanomyography (MMG) has rarely been used to examine coactivation responses during fatiguing tasks. Under some conditions, MMG amplitude (AMP) provides insights into motor unit (MU) recruitment, while MMG mean power frequency (MPF) provides a qualitative description of the global firing rate of the unfused activated motor units. Thus, the purpose of the present study was to use MMG to examine coactivation of the agonist and antagonist muscles during fatiguing reciprocal forearm extension (EXT) and flexion (FLEX) muscle actions. Methods: Ten men (mean ± SD: age = 21.6 ± 1.3 yrs; body mass = 80.9 ± 6.5 kg; height = 179.1 ± 5.9 cm) completed 50 consecutive, maximal, reciprocal, isokinetic forearm EXT and FLEX muscle actions at 60 and 180°·s-1. The AMP and MPF contents of the MMG signals from the biceps (BB) and triceps (TB) were recorded simultaneously throughout the fatiguing task. The MMG and torque values were averaged across 5 consecutive repetitions and normalized to the value from repetition five. A 2 (Speed: 60 and 180°·s-1) x 2 (Muscle: TB and BB) x 2 (Movement: EXT and FLEX) x 10 (Repetitions: 5 - 50) RMANOVA was used to determine mean differences for AMP and MPF. A 2 (Speed) x 2 (Movement) x 10 (Repetitions) RMANOVA was used to determine mean differences for torque. Results: The statistical analyses indicated that for EXT, MMG AMP was greater at 180°·s-1 than 60°·s-1 (p = 0.04) for both the TB and BB. For FLEX, MMG AMP for the TB was greater at 180°·s-1 than 60°·s-1 (p < 0.01), however, there was no significant difference between speeds for the BB. For MMG MPF during EXT, the TB was significantly greater than the BB (p < 0.01). For FLEX, there was no significant difference between muscles. There were significant (p < 0.05) reductions in torque throughout the fatiguing task for both EXT and FLEX. Conclusion: The results indicated that during forearm EXT and FLEX, the faster velocity muscle actions exhibited greater lateral oscillations than the slower velocities, likely due to differences in the contributions of fast and slow fibers to torque production. In addition, the TB exhibited a greater global MU firing rate, as suggested by the MMG MPF responses, than the BB during forearm EXT. Thus, the fatigued-induced decrease in torque was not attributable to changes in coactivation.