Determinants of curvature constant (W') of the power duration relationship under normoxia and hypoxia: the effect of pre-exercise alkalosis.

Purpose: This study investigated the effect of induced alkalosis on the curvature constant (W') of the power-duration relationship under normoxic and hypoxic conditions.

Methods: Eleven trained cyclists (mean ± SD) Age: 32 ± 7.2 years; body mass (bm): 77.0 ± 9.2 kg; VO: 59.2 ± 6.8 ml·kg·min completed seven laboratory visits which involved the determination of individual time to peak alkalosis following sodium bicarbonate (NaHCO) ingestion, an environment specific ramp test (e.g. normoxia and hypoxia) and four x 3 min critical power (CP) tests under different experimental conditions. Participants completed four trials: alkalosis normoxia (ALN); placebo normoxia (PLN); alkalosis hypoxia (ALH); and placebo hypoxia (PLH). Pre-exercise administration of 0.3 g.kg BM of NaHCO was used to induce alkalosis. Environmental conditions were set at either normobaric hypoxia (FiO: 14.5%) or normoxia (FiO: 20.93%).

Results: An increase in W' was observed with pre-exercise alkalosis under both normoxic (PLN: 15.1 ± 6.2 kJ vs. ALN: 17.4 ± 5.1 kJ; P = 0.006) and hypoxic conditions (ALN: 15.2 ± 4.9 kJ vs. ALN: 17.9 ± 5.2 kJ; P < 0.001). Pre-exercise alkalosis resulted in a larger reduction in bicarbonate ion (HCO) concentrations during exercise in both environmental conditions (p < 0.001) and a greater blood lactate accumulation under hypoxia (P = 0.012).

Conclusion: Pre-exercise alkalosis substantially increased W' and, therefore, may determine tolerance to exercise above CP under normoxic and hypoxic conditions. This may be due to NaHCO increasing HCO buffering capacity to delay exercise-induced acidosis, which may, therefore, enhance anaerobic energy contribution.