Slow-wave sleep mediates the compensatory effects of acute moderate-intensity exercise on declarative memory deficits in sleep restriction.

Insufficient sleep impairs cognition, particularly hippocampal-dependent memory. However, effective strategies for addressing these effects in humans remain limited. Physical exercise enhances slow-wave sleep (SWS) and improves memory performance, suggesting it may provide a physiologically grounded buffer against sleep-loss-related memory deficits. Here, we tested whether a single session of moderate-intensity exercise may protect long-term declarative memory following sleep restriction, and whether SWS mediates this effect. Eighty-eight healthy young adults (52% female; 24.0 ± 3.8 years) were randomly assigned to one of four groups based on exercise and sleep opportunity: average sleep (S8: 8.5 hours/night), sleep restriction (S5: 4.5 hours/night), exercise before average sleep (ExS8), and exercise before sleep restriction (ExS5). Participants completed either a 30-min evening moderate-intensity cycling (7: 00 p.m.; 55%-60% VO₂max) or seated rest prior to learning 80 face-name pairs (10:00 p.m.), followed by immediate and delayed recall (120 face-name pairs: 80 studied, 40 novel) after polysomnography-recorded sleep. We found a significant exercise × sleep interaction for delayed recall performance (discriminability index, d'; p = .033, partial η2 = 0.056). The delayed recall d' of the ExS5 was significantly higher than the S5 (p = .028), but was comparable to S8 and ExS8 groups (ps > 0.05). The proportion of SWS mediated the association between exercise and delayed recall d' (B = 0.105, SE = 0.091, 95% bootstrap CI (0.073, 0.924)). These findings indicate that acute moderate-intensity exercise is associated with offsetting the negative impact of sleep restriction on long-term declarative memory in sleep restriction, an effect statistically mediated by SWS percentage.