Author(s): SLUNECKO, M., VOGL, A., BIRATELLE, R., CSAPO, R., Institution: UNIVERSITY OF VIENNA, Country: AUSTRIA, Abstract-ID: 2376

INTRODUCTION:
Poor sleep is common, and shorter sleep duration is consistently associated with impaired physical performance. A prevalent form of sleep loss, sleep fragmentation involving repeated nocturnal awakenings, affects many athletes [1]. However, the effects of acute sleep fragmentation on endurance performance and aerobic capacity have not yet been examined.
METHODS:
Using a counterbalanced cross-over design, 35 (16f/19m, 25.8 ± 4.3 years) healthy, well-trained adults (women: VO2peak = 51.1 ± 8.6 mL·kg⁻¹·min⁻¹; men: VO2peak = 60.0 ± 8.9 mL·kg⁻¹·min⁻¹) completed two consecutive nights of fragmented sleep (FRA; auditory awakenings every two hours) and two nights of habitual sleep (HAB). Prescribed time in bed was kept constant between conditions and individualized according to one week of baseline sleep (BASE). Sleep metrics (nocturnal awakenings, perceived quality, efficiency, time in bed, time asleep) were assessed using diaries and fitness trackers. Each condition was followed by a standardized incremental cardiopulmonary exercise test to exhaustion using a ramp protocol on a cycle ergometer. Identical protocols were applied in both trials, workload was concealed to prevent intentional pacing, and meals were standardized for composition and timing. Peak work rate (WRpeak), peak oxygen uptake (VO2peak), maximal fat oxidation (MFO) and the corresponding intensity, and oxygen uptake and heart rate at both ventilatory thresholds were compared between sleep conditions using paired t-tests (α = 0.05). Effect sized are reported as mean differences (MD).
RESULTS:
The FRA condition resulted in more awakenings (BASE: 0.4 ± 0.6, HAB: 0.3 ± 0.6, FRA: 2.9 ± 1.3, p < .001), lower perceived sleep quality (rated from very poor (1) to very good (10); BASE: 7.3 ± 1.0, HAB: 7.8 ± 1.0, FRA: 5.0 ± 1.8, p < .001) and sleep efficiency (BASE: 94.5 ± 2.1%, HAB: 94.5 ± 2.9%, FRA: 90.9 ± 2.3%, p < .001) compared with HAB and BASE, indicating successful fragmentation. Time in bed (BASE: 7.97 ± 0.72 h, HAB: 8.15 ± 0.91 h, FRA: 7.97 ± 0.95 h, p = .426) and time asleep (BASE: 6.96 ± 0.63 h, HAB: 7.10 ± 0.77 h, FRA: 6.85 ± 0.83 h, p = .234) did not differ. No significant differences between HAB and FRA were found for VO2peak (p = .119, MD = ─0.95 mL·kg⁻¹·min⁻¹ 95%CI [─2.17, 0.26]), WRpeak (p = .245, MD = ─4.20 W 95%CI [─11.4, 3.0]), MFO (p = .087, MD = ─0.038 g·min⁻¹ 95%CI [─0.082, 0.006]), or any of the remaining outcomes.
CONCLUSION:
Two consecutive nights of experimentally induced sleep fragmentation, with time in bed controlled, did not significantly affect endurance performance in cardiopulmonary exercise tests. Participants achieved comparable peak power outputs, and physiological responses were similar across tests. Future studies should investigate whether prolonged sleep fragmentation elicits cumulative effects.
[1] Vitale et al., Int J Spo Med, 2019