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

Pirlot, Thibaud, Thibaud Mihailovic, Philippe Gimenez, Grégoire P Millet, Franck Brocherie, Eric Fruchart, Gilles Ravier, Romain Baron, Sandrine Bouzigon, Emmanuel Guirronnet, Alain 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. 00:00-00, 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.