Sex differences in neuromuscular function after repeated eccentric contractions of the knee extensor muscles.

ABSTRACT

PURPOSE: This study examined the mechanisms for force and power reduction during and up to 48 h after maximal eccentric contractions of the knee extensor muscles in young men and women. METHODS: 13 men (22.8 ± 2.6 years) and 13 women (21.6 ± 2.2 years) performed 150 maximal effort eccentric contractions (5 sets of 30) with the knee extensor muscles at 60° s-1. Maximal voluntary isometric contractions (MVIC) and maximal voluntary concentric contractions (MVCC) were performed before and after the 150 eccentric contractions. The MVCCs involved a set of two isokinetic contractions at 60° s-1 and sets of isotonic contractions performed at seven different resistance loads (1 N m, 10, 20, 30, 40, 50, and 60% MVIC). Electrical stimulation was used during the MVICs and at rest to determine changes in voluntary activation and contractile properties. RESULTS: At baseline, men were stronger than women (MVIC 276 ± 48 vs. 133 ± 37 N m) and more powerful (MVCC 649 ± 77 vs. 346 ± 78 W). At termination of the eccentric contractions, voluntary activation, resting twitch amplitude, and peak power during concentric contractions at the seven loads and at 60° s-1 decreased (P < 0.05) similarly in the men and women. At 48 h post-exercise, the MVIC torque, power (for loads ≥20-60% MVIC), and voluntary activation remained depressed (P < 0.05), but the resting twitch had returned to baseline (P > 0.05) with no sex differences. CONCLUSION: Central mechanisms were primarily responsible for the depressed maximal force production up to 48 h after repeated eccentric contractions of the knee extensors and these mechanisms were similar in men and women.