Exercise modality-specific regulation of sleep stability in mice: An EEG-based comparative study of high-intensity...

Sleep stability is operationally defined here as the continuity and consolidation of sleep over time, reflected tended to by fewer wake-sleep transitions, fewer fragmented bouts, and longer uninterrupted sleep bouts. Sleep duration is treated as a complementary quantity measure rather than, by itself, evidence of improved stability. Exercise is an effective non-pharmacological intervention for sleep, but whether different exercise formats differentially affect these stability-related features, and whether responses differ by sex, remains unclear.

Forty-eight healthy adult C57BL/6 mice, with equal numbers of males and females, were randomly assigned to an untrained control group (UT), a moderate-intensity continuous training group (MICT), or a high-intensity interval training group (HIIT). Long-term in-cage electroencephalographic (EEG) monitoring was performed using the Cerebus multichannel neural signal acquisition system. Continuous 48-h recordings were obtained at baseline, after 4 weeks of intervention, and after 6 weeks of intervention. Sleep-wake states were scored using SleepSign for Animal 3.0. Total sleep time (TST), NREM and REM sleep duration, the number of wake-sleep transitions, defined as the total number of transitions between wakefulness and sleep, and circadian rhythm amplitude were quantified. Linear mixed-effects models (LMMs) were used to analyze the effects of time, group, sex, and their interactions.

HIIT significantly increased TST (β = 18.50, 95% CI: 9.03-27.97, p < 0.001) and NREM sleep duration (β = 19.46, 95% CI: 10.38-28.54, p < 0.001), with the largest changes at week 4. MICT produced a limited increase in TST but reduced wake-sleep transitions and prolonged NREM bout duration, a pattern consistent with lower fragmentation and greater continuity. HIIT-related sleep prolongation was accompanied by longer NREM bouts, but may also represent recovery-related sleep pressure after strenuous exercise. Neither protocol altered the normal circadian phase distribution. Sex-stratified findings were exploratory because of the small within-sex sample size and the absence of estrous-cycle monitoring. Relative to the untrained control group, HIIT showed a more pronounced trend toward increasing total sleep time and NREM sleep duration, whereas MICT tended to reduce sleep fragmentation and wake-sleep transitions and to prolong NREM bout duration. However, direct statistical comparisons between the two exercise modalities did not reach statistical significance after FDR adjustment (Supplementary Table S1). Accordingly, the differential patterns observed between HIIT and MICT should be interpreted as descriptive trends relative to the control condition rather than statistically established modality-specific effects.

MICT and HIIT were associated with different EEG-defined sleep phenotypes. MICT showed the clearest pattern of improved continuity, whereas HIIT tended to increased sleep quantity and prolonged NREM bouts. Because exercise intensity, stress physiology, endocrine status, and molecular mechanisms were not directly measured, these findings should be interpreted as descriptive evidence of modality-associated sleep architecture rather than proof of distinct biological mechanisms. The results support further physiologically validated studies of exercise format and sleep continuity.