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

Abstract

PurposeThis study investigated the effect of induced alkalosis on the curvature constant (W’) of the power-duration relationship under normoxic and hypoxic conditions.MethodsEleven trained cyclists (mean ± SD) Age: 32 ± 7.2 years; body mass (bm): 77.0 ± 9.2 kg; VO2peak: 59.2 ± 6.8 ml·kg−1·min−1 completed seven laboratory visits which involved the determination of individual time to peak alkalosis following sodium bicarbonate (NaHCO3) 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−1 BM of NaHCO3 was used to induce alkalosis. Environmental conditions were set at either normobaric hypoxia (FiO2: 14.5%) or normoxia (FiO2: 20.93%).ResultsAn 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 (HCO3 −) concentrations during exercise in both environmental conditions (p < 0.001) and a greater blood lactate accumulation under hypoxia (P = 0.012).ConclusionPre-exercise alkalosis substantially increased W’ and, therefore, may determine tolerance to exercise above CP under normoxic and hypoxic conditions. This may be due to NaHCO3 increasing HCO3 − buffering capacity to delay exercise-induced acidosis, which may, therefore, enhance anaerobic energy contribution.

Effects of daily ingestion of sodium bicarbonate on acid-base status and anaerobic performance during an altitude sojourn at high altitude: a randomized controlled trial

“…The primary finding of the study was that chronic NaHCO 3 ingestion had a considerable impact on acid-base balance, which resulted in a higher alkalotic state; however, chronic NaHCO 3 ingestion did not significantly influence PTSR-related performance outputs and associated physiological responses. A higher alkalotic acid-base balance prior to exercise under hypoxic conditions has been reported to be related to higher performance output and higher maximum blood lactate values after highintensity exercise [11,16,19]. The suggested mechanism underlying the increased [H + ] buffering from intramuscular to extramuscular compartments may lead to improved protection of intramuscular pH and increased anaerobic energy provision and glycogen utilization [16,50].…”

“…Feriche Fernandez-Castanys et al [22], Hauswirth et al [23], and McLellan et al [24] all described increased or constant exercise performance under acute altitude conditions in hypoxic chambers compared with sea-level performance in subjects receiving alkalizing agent supplements prior to exercise. In addition, Deb et al [11,19] and Gough et al [16] reported positive effects of NaHCO 3 under acute moderate hypoxic conditions at simulated altitude during intermittent and repeated high-intensity exercise. They conclude that NaHCO 3 ingestion may offer an ergogenic strategy to mitigate hypoxia-induced declines in exercise performance.…”

“…Dietary strategies have previously been used to attenuate the impaired exercise performance under hypoxic conditions [11][12][13]. Among these, supplementation with sodium bicarbonate (NaHCO 3 ) as an alkalotic buffer is an interesting approach to alleviate the elevated acidic stress during exercise above the lactate threshold under hypoxic conditions [11].…”

“…Dietary strategies have previously been used to attenuate the impaired exercise performance under hypoxic conditions [11][12][13]. Among these, supplementation with sodium bicarbonate (NaHCO 3 ) as an alkalotic buffer is an interesting approach to alleviate the elevated acidic stress during exercise above the lactate threshold under hypoxic conditions [11]. In normoxic conditions, NaHCO 3 is proposed to enhance anaerobic exercise performance by increasing the availability of blood [HCO 3 − ], thereby strengthening the physiochemical buffering capacity to reduce the rate of hydrogen cation ([H + ]) production during exercise [11,14,15].…”

“…Among these, supplementation with sodium bicarbonate (NaHCO 3 ) as an alkalotic buffer is an interesting approach to alleviate the elevated acidic stress during exercise above the lactate threshold under hypoxic conditions [11]. In normoxic conditions, NaHCO 3 is proposed to enhance anaerobic exercise performance by increasing the availability of blood [HCO 3 − ], thereby strengthening the physiochemical buffering capacity to reduce the rate of hydrogen cation ([H + ]) production during exercise [11,14,15]. However, while the results of some studies have suggested that significant increases in [H + ] may impair subsequent exercise performance by reducing the capacity for muscle force production [16,17], the results of other studies suggest that exercise performance may be unaffected by disturbances in acid-base balance [18]; thus, there remains no consensus in the literature regarding the roles of acid-base status in anaerobic exercise performance and skeletal muscle fatigue.…”