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

Abstract

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 NaHCO₃ 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 (TT₁ and TT₂) 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 NaHCO₃ (SBC2), 0.3 g kg⁻¹ BM NaHCO₃ (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 ([HCO₃⁻]). Each TT series was also completed in a normobaric hypoxic chamber set at 14.5% FiO₂ (~ 3000 m).

Results

Performance was improved following SBC3 in both TT₁ (400.2 ± 24.1 vs. 405.9 ± 26.0 s; p = 0.03) and TT₂ (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 TT₁ (402.3 ± 26.5 s; p = 0.15) and TT₂ (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

NaHCO₃ ingestion improves repeated exercise performance in acute hypoxic conditions, although the optimal dose is likely to be 0.3 g kg⁻¹ BM.

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