Neurophysiological and neuromuscular responses associated with the repeated bout effect following eccentric exercise in healthy adults: a systematic review and meta-analysis.

Muscle damage severity decreases after repeated eccentric exercise bouts (the repeated bout effect [RBE]), but whether accompanying neural and neuromuscular changes contribute to protection or arise secondary to reduced damage remains unclear. This systematic review and meta-analysis compared neurophysiological and neuromuscular responses between initial and repeated eccentric bouts in healthy adults. Eight databases were searched from November 1990 to January 2025, and Hedges' g was calculated where outcomes were comparable. Given the small number of contributing studies, all pooled analyses were considered exploratory. Twelve studies met the inclusion criteria. Twitch/evoked force showed recovery-compatible point estimates at 24 h (g = 1.02, 95% CI -0.03-2.06) and 48 h (g = 0.50, 95% CI 0.08-0.92). Voluntary activation findings were mixed. TMS-derived voluntary activation produced positive single-study estimates at 24 h (g = 1.10, 95% CI 0.29-1.92) and 48 h (g = 1.06, 95% CI 0.26-1.87), whereas pooled ITT-derived estimates were imprecise at 24 h (g = 0.36, 95% CI -0.92-1.63) and recovery-compatible but based on only two studies at 48 h (g = 0.44, 95% CI 0.03-0.85). M-wave/Mmax showed no consistent between-bout pattern. Corticospinal, intracortical, spinal, reticulospinal, motor-unit and EMG findings were limited, inconsistent or directionally unclear. Neural and neuromuscular changes accompany the RBE, but whether they contribute to protection or reflect reduced damage remains unresolved. Peripheral contractile outcomes showed the most consistent recovery-compatible pattern, whereas evidence concerning central activation and motor-unit behaviour remained limited or inconsistent.