Increasing the resting time between drop jumps lessens delayed-onset muscle soreness and limits the extent of prolonged low-frequency force depression in human knee extensor muscles.

Abstract

Unaccustomed eccentric contractions generally result in a long-lasting contractile impairment, referred to as prolonged low-frequency force depression (PLFFD), and delayed-onset muscle soreness (DOMS). We here used repeated drop jumps (DJs) as an eccentric contraction model and studied the effects of increasing the time between DJs from 20s to 5min. We hypothesized that both PLFFD and DOMS would be less marked at the longer DJ interval due to the longer time to restore structural elements between DJs. Young men (n = 12) randomly performed 50 DJs with either 20-s (DJ-20s) or 5-min (DJ-5min) rest between DJs. Voluntary, 20Hz and 100Hz electrically stimulated isometric knee extension torques and muscle soreness were monitored before and for 7days after DJs; serum CK activity was measured to assess muscle fibre protein leakage. In additional experiments, changes in mRNA levels were assessed in muscle biopsies collected before and 1h after exercise. A marked PLFFD was observed with both protocols and the extent of 20Hz torque depression was smaller immediately and 1day after DJ-5min than after DJ-20s (p < 0.05), whereas the MVC and 100Hz torques were similarly decreased with the two protocols. Markedly larger differences between the two protocols were observed for the muscle soreness score, which 1-4days after exercise was about two times larger with DJ-20s than with DJ-5min (p < 0.01). The larger protective effect of the longer DJ interval against DOMS than against PLFFD indicates that their underlying mechanisms involve different structural elements.