Interactions between exposure to hypoxia and the training-induced autonomic adaptations in a “live high–train low” session

The autonomic and cardiovascular adaptations to hypoxia are opposite to those resulting from aerobic training. We investigated (1) whether exposure to hypoxia in a live high–train low (LHTL) session limits the autonomic and cardiovascular adaptations to training, and (2) whether such interactions remain 15 days after the end of the LHTL. Eighteen national swimmers trained for 13 days at 1,200 m, living (16 h day⁻¹) either at 1,200 m (live low–train low, LLTL) or at a simulated height of 2,500–3,000 m (LHTL). Subjects were investigated at 1,200 m before and at the end of the training session, and after the following 15 days of sea-level training. Cardiovascular parameters and the autonomic control assessed by spectral analysis of R–R and diastolic blood pressure (DBP) variability were obtained in the resting supine position and in response to an orthostatic test. At the end of the 13-day training, resting heart rate (HR) and sympathetic modulation on heart decreased in LLTL (−10.1% and −25.4%, P<0.01, respectively) but not in LHTL (−5.8, −15.5%, respectively). Total peripheral resistance (TPR) and DBP became higher in LHTL than in LLTL (P<0.05). Stroke index decreased in both groups during the tilt test, counteracted by an increase in HR and sympathetic modulation to the heart and vasculature, and a decrease in vagal modulation to the heart. After the following 15-day sea-level training, differences in TPR and DBP between groups disappeared. During an LHTL session, adaptations to hypoxia interacted with the autonomic and cardiovascular adaptations to training. However, these interactions did not limit the adaptations to the following sea-level training.