Exercise-Induced Autonomic and Cardio-Respiratory Stress at High Altitude in Leisure Athletes

Kolokas, Iraklis, Jenny Schlichtiger, Sara Jamali, Lina Kronschnabel, Paul Adam, Jeremias Götschke, Pontus Mertsch, Christian Goelz, Solveig Vieluf, and Stefan Brunner. Exercise-induced autonomic and cardio-respiratory stress at high altitude in leisure athletes. High Alt Med Biol. 00:00–00, 2026. Background: Exercise at high altitude imposes additional cardiovascular and autonomic demands on leisure athletes. We investigated how acute exposure to high altitude alters cardiovascular, respiratory, and autonomic regulation during rest, exercise start, and peak exercise. Methods: Briefly, 12 nonacclimatized participants (five female) performed standardized exercise tests at low and high altitude, while heart rate (HR), respiratory rate (RR), heart rate variability (HRV_RMSSD), respiratory rate variability (RRV_RMSSD), and respiratory sinus arrhythmia (RSA) were measured using wearable electrocardiogram (ECG) recordings and computer-based signal analysis. Results: Maximal power output during the maximal incremental cycling test was lower at high altitude (235.5 ± 65.5 W) compared to low altitude (276.4 ± 77.5 W). HR and RR increased with exercise intensity and showed a nonsignificant increase at high altitude. RMSSD decreased during exercise (−116.67 ± 79.29 ms, p < 0.01) and at high altitude (−50.16 ± 91.55 ms, p = 0.015), with a significant interaction during exercise at high altitude ( p < 0.01), while RRV remained relatively stable. RSA was reduced at high altitude (−1.1 ± 0.71 bpm, p = 0.028) and during exercise (−4.37 ± 0.38 bpm, p < 0.01), reflecting lower cardio-respiratory coupling. Conclusion: These patterns indicate that acute high-altitude exercise shifts autonomic balance, imposing heightened cardiac strain while the respiratory system maintains adaptive ventilatory flexibility, highlighting their differential roles in supporting oxygen delivery and systemic homeostasis under hypoxic stress.