Influence of Normobaric Hypoxia on Maximal Force Production Following High-Intensity Resistance Circuit Training

Background: Previous research suggests that resistance training in hypoxia can cause physiological and muscle adaptations. However, this method may not be efficient for individuals who are training to optimize maximal strength and power. Objective: This study aimed to investigate the effects of 8 weeks of high-intensity resistance circuit in normobaric hypoxic conditions on maximal and explosive measures of muscle strength in upper and lower limbs. Methods: A total of 28 subjects were randomly assigned to either hypoxia (fraction of inspired oxygen [F_IO₂] = 15%; HRC_hyp: n = 15; age: 24.6 ± 6.8 years; height: 177.4 ± 5.9 cm; weight: 74.9 ± 11.5 kg) or normoxia [F_IO₂] = 20.9%; HRC_norm: n = 13; age: 23.2 ± 5.2 years; height: 173.4 ± 6.2 cm; weight: 69.4 ± 7.4 kg) groups. Training sessions consisted of two blocks of three exercises and the training intensity was fixed performed at six repetition maximum. Participants exercised twice weekly for 8 weeks, and upper and lower body power tests were performed before and after the training program. The statistical analysis applied was a two-way analysis of variance with repeated measures and Bonferroni post hoc. Results: No significant differences were observed between groups. However, the hypoxia group showed higher intra-group differences in absolute (N) (F = 7.97; Δ7.3%; p < 0.05; ES = 0.49) and relative (N/Kg) (F = 8.34; Δ7.2%; p < 0.05; ES = 0.49) maximum push-up force after the training period. Conclusions: Hypoxic circuit training may improve a specific upper body performance outcome, but no clear advantage over normoxia was observed.