The influence of alkalosis on repeated high-intensity exercise performance and acid-base balance recovery in acute moderate hypoxic conditions

Purpose: Exacerbated hydrogen cation (H ⁺) production is suggested to be a key determinant of fatigue in acute hypoxic conditions. This study, therefore, investigated the effects of NaHCO ₃ ingestion on repeated 4 km TT cycling performance and post-exercise acid–base balance recovery in acute moderate hypoxic conditions. Methods: Ten male trained cyclists completed four repeats of 2 × 4 km cycling time trials (TT ₁ and TT ₂) with 40 min passive recovery, each on different days. Each TT series was preceded by supplementation of one of the 0.2 g kg ⁻¹ BM NaHCO ₃ (SBC2), 0.3 g kg ⁻¹ BM NaHCO ₃ (SBC3), or a taste-matched placebo (0.07 g kg ⁻¹ BM sodium chloride; PLA), administered in a randomized order. Supplements were administered at a pre-determined individual time to peak capillary blood bicarbonate concentration ([HCO ₃ ⁻]). Each TT series was also completed in a normobaric hypoxic chamber set at 14.5% FiO ₂ (~ 3000 m). Results: Performance was improved following SBC3 in both TT ₁ (400.2 ± 24.1 vs. 405.9 ± 26.0 s; p = 0.03) and TT ₂ (407.2 ± 29.2 vs. 413.2 ± 30.8 s; p = 0.01) compared to PLA, displaying a very likely benefit in each bout. Compared to SBC2, a likely and possible benefit was also observed following SBC3 in TT ₁ (402.3 ± 26.5 s; p = 0.15) and TT ₂ (410.3 ± 30.8 s; p = 0.44), respectively. One participant displayed an ergolytic effect following SBC3, likely because of severe gastrointestinal discomfort, as SBC2 still provided ergogenic effects. Conclusion: NaHCO ₃ ingestion improves repeated exercise performance in acute hypoxic conditions, although the optimal dose is likely to be 0.3 g kg ⁻¹ BM.