Psychological, Sleep, and Heart Rate Variability Responses During Early- and Middle-Term Acclimatization of "Living...

Pirlot, Thibaud, Thibaud Mihailovic, Philippe Gimenez, Grégoire P. Millet, Franck Brocherie, Eric Fruchart, Gilles Ravier, Bertrand Baron, Romain Bouzigon, Sandrine Guirronnet, Emmanuel Brunet, and Alain Groslambert. Psychological, sleep, and heart rate variability responses during early- and middle-term acclimatization of "Living High-Training Low and High". High Alt Med Biol. 26:291-300, 2025. Background: This study investigated the relationships between psychological responses, sleep, and heart rate variability (HRV) before and during a "living high-training low and high" (LHTLH) camp. Methods: Ten elite female cyclists (mean ± SD, age = 17.3 ± 1.2 years, VO₂max = 54.9 ± 6.9 ml·min/kg) were monitored for 19 days divided into three periods: (1) normoxia (5 days preceding LHTLH), (2) early acclimatization period (days 1-4 of LHTLH), and (3) middle acclimatization period (days 5-14 of LHTLH) in normobaric hypoxic chambers set at a simulated altitude of 2,800 m. During the intervention, their training load (TL), sleep disturbance, psychological (stress, activation state, and perseverance) and physiological responses (sleep architecture, nocturnal peripheral oxygen saturation [SpO₂], and HRV) were monitored. Results: In normoxia, no significant correlations were observed between TL and any psychological and physiological responses. However, in the early acclimatization period, significant correlations were found between sleep disturbance and SpO₂ (r = -0.83, p < 0.005) and between achieving objectives and HRV (r = -0.91, p < 0.005). In the middle acclimatization period, significant correlations were found between the feeling during training and SpO₂ (r = 0.83; p < 0.005). Conclusion: This indicates that LHTLH exacerbates the psychophysiological interactions during the early acclimatization period that disappear during the middle acclimatization period while others appear.