The Effects of Intermittent Normobaric Hypoxia Training on

[[abstract]]Objective: Interval normobaric hypoxic training (IHT) consists of repeated (three to more times) short periods (5-15 min each) of steady or progressive hypoxia, interrupted by similar periods of rest/recovery. Aim: to determine the effects of IHT on aerobic endurance and cardiac autonomic modulation in adolescents. Method: Thirty male adolescents completed a 15 days IHT regimen (5:5-min hypoxia-to-normoxia ratio for 60 min) of intermittent normobaric hypoxia (12%O2) combining 65% peak oxygen comsumption (V ? O2peak) (IH+E), intermittent normobaric normoxia (21%O2) combining 65% V ? O2peak (IN+E) or intermittent normobaric hypoxia (12%O2) only at rest (IH). Transfer function analysis of heart rate variability (HRV) and respiration were measured during IHT used to characterize low- (mainly sympathetic) and high-frequency (vagal) cardiovascular fluctuations. Before and after IHT experimental protocol, we recorded body composition and hematologic indexes at rest in the morning. Subjects were performed the incremental exercise test. Lactate threshold (LT), V ? O2peak and catecholamines changes (CAs) were determined to refer as the aerobic capacity. Results: (1)There were significantly increased hematologic indexes in EPO (23%), reticularcyte count (10.4%) and hemoglobin (14.7%) after IHT in IH+E. (2)No significant changes were found on body composition. (3)The performances of LT (43.9%) and relatived V ? O2peak（ 26.7%）were improved after IHT in IH+E. Plasma noradrenaline level after exhaustion test were increasing 206.2% significantly in IH+E. (4) IHT decreased sympathovagal tone in the initial stage and recovered progressively in later period. Chronic IHT combining exercise induced better sympathovagal balance, leading to greater tolerance of chronic hypoxia. Conclusion: These results suggested that exercise in combination with IHT might have a benefit for the aerobic performance and cardiac autonomic modulation.