The objective of this study was to test the hypothesis that high-intensity hypoxic training improves sea-level performances more than equivalent training in normoxia. Sixteen well-trained collegiate and Masters swimmers (10 women, 6 men) completed a 5-wk training program, consisting of three high-intensity training sessions in a flume and supplemental low- or moderate-intensity sessions in a pool each week. Subjects were matched for gender, performance level, and training history, and they were assigned to either hypoxic [Hypo; inspired O2 fraction (Fi O2 ) = 15.3%, equivalent to a simulated altitude of 2,500 m] or normoxic (Norm; Fi O2 = 20.9%) interval training in a randomized, double-blind, placebo-controlled design. All pool training occurred under Norm conditions. The primary performance measures were 100- and 400-m freestyle time trials. Laboratory outcomes included maximal O2 uptake (V˙o 2 max), anaerobic capacity (accumulated O2 deficit), and swimming economy. Significant ( P = 0.02 and <0.001 for 100- and 400-m trials, respectively) improvements were found in performance on both the 100- [Norm: −0.7 s (95% confidence limits: +0.2 to −1.7 s), −1.2%; Hypo: −0.8 s (95% confidence limits: −0.1 to −1.5 s), −1.1%] and 400-m freestyle [Norm: −3.6 s (−1.8 to −5.5 s), −1.2%; Hypo: −5.3 s (−2.3 to −8.3 s), −1.7%]. There was no significant difference between groups for either distance (ANOVA interaction, P = 0.91 and 0.36 for 100- and 400-m trials, respectively). V˙o 2 max was improved significantly (Norm: 0.16 ± 0.23 l/min, 6.4 ±8.1%; Hypo: 0.11 ± 0.18 l/min, 4.2 ± 7.0%). There was no significant difference between groups ( P = 0.58). We conclude that 5 wk of high-intensity training in a flume improves sea-level swimming performances andV˙o 2 max in well-trained swimmers, with no additive effect of hypoxic training.
High‐intensity training in normobaric hypoxia enhances exercise performance and aerobic capacity in Thoroughbred horses: A randomized crossover study
