Hypoxia matters: comparison of external and internal training load markers during an 8-week resistance training program in normoxia, normobaric hypoxia and hypobaric hypoxia

Purpose To compare external and internal training load markers during resistance training (R T ) in normoxia (N), intermittent hypobaric hypoxia (HH), and intermittent normobaric hypoxia (NH). Methods Thirty-three volunteers were assigned an 8-week R T program in either N (690 m, n = 10), HH (2320 m, n = 10), or NH (inspired fraction of oxygen = 15.9%; ~ 2320 m, n = 13). The R T program (3x/week) consisted of six exercises, with three sets of six to 12 repetitions at ~ 70% of one repetition maximum (1RM) with the first session of each week used for analysis. 1RM in back squat and bench press was used to evaluate muscle strength before and after the program. External load was assessed by the volume load relative to body mass (RVL, kg·kg −1 ). Internal load was assessed by the ratings of perceived exertion (RPE) and heart rate (HR). Results Smaller relative improvements were found for the back squat in the N group (11.5 ± 8.8%) when compared to the NH group (22.2 ± 8.2%, P = 0.01) and the HH group (22 ± 8.1%, P = 0.02). All groups showed similar RVL, HR responses and RPE across the program ( P ˃0.05). However, reduced HR recovery values, calculated as the difference between the highest HR value (HR peak ) and the resting heart rate after a two min rest, were seen in the N and NH groups across the program ( P $$<$$ < 0.05). Conclusion It seems that 8 weeks of intermittent R T in hypoxic environments could maximize time-efficiency when aiming to improve strength levels in back squat without evoking higher levels of physiological stress. Performing R T at hypobaric hypoxia may improve the cardiorespiratory response, which in turn could speed recovery.