Neuromuscular responses to isometric, concentric and eccentric contractions of the knee extensors at the same torque-time integral.

Abstract

The present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters. Healthy men (18-24years) were placed to either isometric (ISO), concentric (CONC), or eccentric (ECC) group (n = 11/group) that performed corresponding contractions of the knee extensors to exert the same amount of torque-time integral (24,427 ± 291 Nm·s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10Hz and 100Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1h, 1day and 2days after each exercise, and were compared among the groups. MVC torque decreased immediately after ISO (-17.0 ± 8.3%), CONC (-21.7 ± 11.5%) and ECC (-26.2 ± 15.6%) similarly (p = 0.35), but the decrease sustained longer (p < 0.05) for ECC (2days post-exercise: -12.9 ± 14.8%) and ISO (-5.5 ± 7.9%) than CONC (+ 5.0 ± 11.0%). Muscle soreness developed after ECC (25.1 ± 19.8mm) and ISO (17.5 ± 21.0mm) similarly (p = 0.15). Voluntary activation decreased immediately (-3.7 ± 6.6%) and 1h post-exercise (-4.7 ± 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (-30.1 ± 15.6%) and 1h post-exercise (-35.0 ± 12.8%) for ECC than others, and the decrease in 10/100Hz ratio was also greater immediately (-30.5 ± 12.6%) and 1h after ECC (-23.8 ± 10.3%) than others. ISO, CONC and ECC with the same torque-time integral produced similar neuromuscular fatigue at immediately post-exercise, but the force loss was longer-lasting after ISO and ECC than CONC, and the changes in peripheral fatigue parameters were the greatest after ECC, suggesting greater muscle damage.