Author(s): SOUSA, A., BARREIRA, J.1,2, CUNHA, L.1,2, COSTA, J.3, MILHEIRO, J.4, VIANA, J.L.1,2, FIGUEIREDO, P.1,5, Institution: UNIVERSITY OF MAIA, Country: PORTUGAL, Abstract-ID: 314

INTRODUCTION:
The implementation of high-intensity interval training (HIIT) within altitude/hypoxic training environments has recently emerged as a novel tool to boost both individual and team sports performance (1, 2). Such training method can be physically challenging, imposing a greater stress on athletes. Thus, ensuring optimal recovery during these intense training periods is essential, with sleep playing a vital role despite being relatively underexplored. This study examined the effects of 4-weeks of HIIT and repeated sprint training (RST) in a simulated hypoxia setting on sleep and nocturnal heart rate variability (NHRV).
METHODS:
Eight well-trained subjects (mean ± SD age: 38.8 ± 4.6 yrs) were either assigned to the normoxia (CON: n=4) or hypoxia (HYP: n=4) condition after having their sleep monitored for 2 weeks (baseline). Then, for 4 weeks, participants performed 3 training sessions (HIIT=2, RST=1) each week in either a normoxia or simulated hypoxia setting (intervention). Sleep was objectively monitored through wrist-worn actigraphy devices, and NHRV was monitored through heart rate (HR) monitors. Comparison between groups, study phase (baseline and intervention) and the type of day (baseline, exercise, and rest) were examined.
RESULTS:
Overall, sleep duration was 452.5 (95% CI 440.0; 464.9) minutes and sleep efficiency 90.5 (89.8; 91.2) %. Resting HR was 50.3 (49.3; 51.3) bpm and NHRV 4.3 (4.2; 4.4) ms. There were similar results (p>0.05) in sleep and NHRV between baseline and intervention period in any group, besides wake-up time, which was earlier during the intervention for the CON group (p = 0.008, d = 0.47).
CONCLUSION:
Although subjects’ average sleep duration throughout the duration of the study was within current recommendations for healthy adults (7 or more hours per night on a regular basis), large heterogeneity in sleep variables and schedules was observed. Moreover, and compared with the baseline period, sleep and NHRV was not impacted to a larger extent when 4-weeks of HIIT and RST were held in simulated hypoxia conditions, when compared with the condition where the training design was held in normoxia.

Acknowledgements
Portuguese Foundation for Science and Technology (SFRH/BPD/114670/2016 and UID/04045/2020).

References
(1) Brocherie, F., et al (2017). Sports Medicine, 47(8):1651-1660.
(2) Girard, O., et al (2017). Sports Medicine, 47(10):1931-1949