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

Abstract

This study examined the mechanisms for force and power reduction during and up to 48h after maximal eccentric contractions of the knee extensor muscles in young men and women. 13 men (22.8 ± 2.6years) and 13 women (21.6 ± 2.2years) 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 (1Nm, 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. At baseline, men were stronger than women (MVIC: 276 ± 48 vs. 133 ± 37Nm) and more powerful (MVCC: 649 ± 77 vs. 346 ± 78W). 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 48h 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. Central mechanisms were primarily responsible for the depressed maximal force production up to 48h after repeated eccentric contractions of the knee extensors and these mechanisms were similar in men and women.