Repeated-sprint exercise in hypoxia does not alter sleep quality in young male adults

To investigate the effect of repeated-sprint exercise in hypoxia on sleep quality. Ten healthy young male adults performed three trials on different days: repeated-sprint exercise in normoxia (NOR, fraction of inspired oxygen [FiO 2 ] 20.9%), repeated-sprint exercise in hypoxia (HYP, FiO 2 14.5%), and no exercise in normoxia (REST, FiO 2 20.9%). In NOR and HYP, trials were performed between 4:30 PM and 6:00 PM, consisting of 30 min of submaximal pedaling followed by two sets of repeated sprints (6 × 6-s with 30-s rest). During sleep, heart rate (HR), HR variability ( e.g., the percentage of adjacent R-R intervals > 50 ms [pNN50]), skin temperature were monitored and sleep quality was assessed via electroencephalography. Total sleep time, sleep efficiency, sleep latency, duration of each sleep stage (non-REM [sleep stage without rapid eye movement] stages 1–3, REM) did not significantly differ among the three trials. During the first 90 min of sleep, HR was significantly higher in HYP (53 ± 2 bpm) than in REST (49 ± 1 bpm, P < 0.05). Furthermore, pNN50 was significantly lower in both HYP (48.8 ± 4.8%) and NOR (50.4 ± 4.9%) than in REST (58.3 ± 3.6%, P < 0.05). Performing repeated-sprint exercise in hypoxia in the early evening altered HRV-derived indices during the first 90 min of sleep, without markedly affecting sleep quality.