Comparison between Eccentric-Only and Coupled Concentric-Eccentric Contractions for Neuromuscular Fatigue and Muscle Damage

Purpose Eccentric contractions induce muscle damage, but less is known about the effects of preceding concentric contractions to eccentric contractions on muscle damage. We compared eccentric-only (ECC) and coupled concentric and eccentric contractions (CON-ECC) of the knee extensors for parameters of neuromuscular fatigue and muscle damage. Methods Twenty participants (age, 19-36 yr) were randomly placed into an ECC or a CON-ECC group (n = 10 per group), without significant (P > 0.06) differences in baseline neuromuscular variables between groups. The ECC group performed six sets of eight ECC at 80% of ECC one-repetition maximum (1-RMecc), whereas the CON-ECC group performed six sets of eight alternating concentric (CON) and ECC (16 contractions per set) at 80% of CON 1-RM and 1-RMecc, respectively. Maximal voluntary isometric contraction force, rate of force development, resting twitch force, maximal M-wave (M-MAX), voluntary activation, motor evoked potentials, corticospinal silent period, short interval intracortical inhibition, and muscle soreness were measured before, immediately after, and 1-3 d after exercise. Results No significant (P >= 0.09) differences between ECC and CON-ECC were observed for changes in any variables after exercise. However, maximal voluntary isometric contraction force decreased immediately after exercise (ECC: -20.7% +/- 12.8%, CON-ECC: -23.6% +/- 23.3%) and was still reduced 3 d after exercise (ECC: -13.6% +/- 13.4%, CON-ECC: -3.3% +/- 21.2%). Rate of force development at 0-30 ms reduced immediately after exercise (ECC: -38.3% +/- 33.9%, CON-ECC: -30.7% +/- 38.3%). Voluntary activation, resting twitch force, and motor evoked potential/M-MAX decreased and corticospinal silent period increased after exercise (all P <= 0.03), but short interval intracortical inhibition and M-MAX did not change. Muscle soreness developed (P < 0.001) similarly for both groups (peak, 38.5 +/- 29.5 mm). Conclusions CON-ECC did not exacerbate neuromuscular fatigue and muscle damage when compared with ECC, despite twice as many contractions performed. Thus, eccentric contractions (n = 48 in both groups) seemed to mainly mediate the neuromuscular responses observed.

Automated summary

This study investigated the effects of concentric and eccentric contractions on neuromuscular fatigue and muscle damage, and found that coupled concentric and eccentric contractions did not exacerbate these issues, despite performing twice the number of contractions compared to eccentric-only contractions.