Pre-Sleep Casein Protein and Next-Day Muscle Soreness and Performance Recovery in Resistance-Trained and Competitive Athletes: A Systematic Review

Abstract

Casein protein is a slow-digesting milk protein hypothesised to attenuate the overnight decline in muscle protein synthesis (MPS) that follows resistance exercise. Because strength/power athletes typically train in the evening and rely on rapid next-day performance restoration, pre-sleep casein has been proposed as a practical nutritional strategy to reduce delayed-onset muscle soreness (DOMS) and accelerate performance recovery. This study examines the effect of pre-sleep casein protein ingestion on next-day muscle soreness and performance recovery indices (maximal strength, power, jump performance, and biochemical markers of muscle damage) in resistance-trained and competitive strength/power-relevant athletes. Eight electronic databases were searched from January 2015 to December 2025. Nine primary studies (N=235 participants) met eligibility criteria. Chronic (12-week) pre-sleep casein ingestion combined with progressive resistance training augmented gains in muscle strength and cross-sectional area relative to placebo. In acute, single-session paradigms, benefit for next-day soreness and functional performance recovery (countermovement jump, reactive strength index, pressure-pain threshold) was most consistently observed when casein (30–40 g) was ingested close to a late-evening/night-time training or competition bout, particularly in team-sport and mixed-methods designs. Conversely, several well-controlled trials in resistance-trained men and women, and studies in which the damaging exercise bout occurred in the morning, reported no significant between-group differences in soreness, maximal voluntary contraction, or 1-repetition-maximum performance the following day. Pre-sleep casein protein ingestion appears to support chronic strength and hypertrophy adaptations and may accelerate acute functional recovery when administered shortly after evening/night-time resistance-type or high-intensity exercise, but current evidence does not support a uniform, clinically meaningful reduction in next-day muscle soreness across all resistance-trained populations. The evidence base remains concentrated in recreationally resistance-trained adults and professional team-sport/endurance athletes; dedicated trials in competitive powerlifters, Olympic weightlifters, and other dedicated strength/power-sport specialists are still sparse and are warranted to confirm generalisability to that specific population.