Abstract: The effects of intermittent hypoxic exposure (IHE) on cerebral and muscle oxygenation, arterial oxygen saturation (SaO2), and respiratory gas exchange during a 20-km cycle time trial (20TT) were examined (n = 9) in a placebo-controlled randomized design. IHE (7:3 min hypoxia to normoxia) involved 90-min sessions for 10 days, with SaO2 clamped at ~80%. Prior to, and 2 days after the intervention, a 20TT was performed. During the final minute of the 20TT, in the IHE group only, muscle oxyhemoglobin (oxy-Hb) was elevated (mean ± 95% confidence interval 1.3 ± 1.2 µM, p = 0.04), whereas cerebral oxy-Hb was reduced (-1.9% ± 1.0%, p < 0.01) post intervention compared with baseline. The 20TT performance was unchanged between groups (p = 0.7). In the IHE group, SaO2 was higher (1.0 ± 0.7?%, p = 0.006) and end-tidal PCO2 was lower (-1.2 ± 0.1 mm Hg, p = 0.01) during the final stage of the 20TT post intervention compared with baseline. In summary, reductions in muscle oxy-Hb and systemic SaO2 occurring at exercise intensities close to maximal at the end of a 20TT were offset by IHE, although this was not translated into improved performance.
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