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

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 degrees 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 degrees 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 degrees 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.