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

Purpose The present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters. Method Healthy men (18-24 years) 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 center dot s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10 Hz and 100 Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1 h, 1 day and 2 days after each exercise, and were compared among the groups. Results 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 (2 days 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 +/- 19.8 mm) and ISO (17.5 +/- 21.0 mm) similarly (p = 0.15). Voluntary activation decreased immediately (- 3.7 +/- 6.6%) and 1 h post-exercise (- 4.7 +/- 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (- 30.1 +/- 15.6%) and 1 h post-exercise (- 35.0 +/- 12.8%) for ECC than others, and the decrease in 10/100 Hz ratio was also greater immediately (- 30.5 +/- 12.6%) and 1 h after ECC (- 23.8 +/- 10.3%) than others. Conclusion 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.