Areej Rashid

Background: Exercise-induced muscle damage (EIMD) following unaccustomed resistance training manifests as elevated muscle soreness, reduced functional capacity, and increased circulating biomarkers such as creatine kinase (CK). Protein supplementation is proposed to attenuate these responses through enhanced amino acid availability, yet the evidence base is inconsistent and underpowered for sex-specific effects. Aim: This study examined whether short-term protein supplementation moderates EIMD, delayed-onset muscle soreness (DOMS), and functional recovery in males and females. Methods: Forty healthy, recreationally active adults (20 males, 20 females) completed a muscle-damaging resistance exercise protocol (leg extensions and drop jumps) and were randomised, in a double-blind manner, to consume either whey protein supplement (1 g·kg⁻¹·day⁻¹) or isocaloric maltodextrin (placebo) for three days, in addition to their normal diet. Outcomes included serum CK, DOMS ratings, countermovement jump (CMJ) performance, and leg extension repetitions to fatigue, assessed at baseline, 24h, and 48h. Results: Robust time effects were observed across all outcomes. CK rose markedly at 24–48 h (p < 0.001) with no clear difference between supplements. DOMS increased significantly over time, with a significant Time × Condition effect indicating a smaller increase at 24 h in the protein group (p = 0.027). CMJ declined at 24 h, with females demonstrating smaller decrements than males (Time × Sex, p = 0.032). Protein supplementation also showed a near-significant protective trend for CMJ overall (p = 0.059). Leg extension repetitions to fatigue declined at 24 h in all groups, with no significant sex or supplementation interactions. Conclusion: Protein supplementation significantly influenced perceived soreness and showed a near-significant tendency to support CMJ recovery, but did not significantly alter CK or repetition-based performance. Females exhibited smaller decrements in CMJ compared with males, suggesting a possible sex-related difference in functional recovery following EIMD. Confounders such as habitual protein intake may have limited the magnitude of the observed effects. Further adequately powered, sex-stratified trials are needed.