Increases in M-wave latency of biceps brachii after elbow flexor eccentric contractions in women

Abstract

Eccentric contractions (ECCs) induce muscle damage that is indicated by prolonged loss of muscle function and delayed onset muscle soreness. It is possible that ECCs affect motor nerves, and this may contribute to the prolonged decreases in force generating capability. The present study investigated the hypothesis that M-wave latency of biceps brachii would be increased after maximal elbow flexor ECCs resulting in prolonged loss of muscle strength. Fifteen women performed exercise consisting of 60 maximal ECCs of the elbow flexors using their non-dominant arm. M-wave latency was assessed by the time taken from electrical stimulation applied to the Erb's point to the onset of M-wave of the biceps brachii before, immediately after, and 1-4days after exercise. Maximal voluntaryisometric contraction (MVC) torque, range of motion (ROM) and muscle soreness using a numerical rating scale were also assessed before and after exercise. Prolonged decreases in MVC torque (1-4days post-exercise: -54 to -15%) and ROM (1-2days: -32 to -22%), and increased muscle soreness (peak: 4.2 out of 10) were evident after exercise (p<0.05). The M-wave latency increased (p<0.01) from 5.8±1.0ms before exercise to 6.5±1.7ms at 1day and 7.2±1.5ms at 2days after exercise for the exercised arm only. No significant changes in M-wave amplitude were evident after exercise. The increased M-wave latency did not fully explain the prolonged decreases in MVC torque after eccentric exercise, but may indicate reversible motor nerve impairment.