Acidosis, but Not Alkalosis, Affects Anaerobic Metabolism and Performance in a 4-km Time Trial.

ABSTRACT

PURPOSE: This study aimed to determine the effect of preexercise metabolic acidosis and alkalosis on power output (PO) and aerobic and anaerobic energy expenditure during a 4-km cycling time trial (TT). METHODS: Eleven recreationally trained cyclists (V˙O2peak 54.1 ± 9.3 mL·kg·min) performed a 4-km TT 100 min after ingesting in a double-blind matter 0.15 g·kg of body mass of ammonium chloride (NH4Cl, acidosis), 0.3 g·kg of sodium bicarbonate (NaHCO3, alkalosis), or 0.15 g·kg of CaCO3 (placebo). A preliminary study (n = 7) was conducted to establish the optimal doses to promote the desirable preexercise blood pH alterations without gastrointestinal distress. Data for PO, aerobic and anaerobic energy expenditure, and blood and respiratory parameters were averaged for each 1 km and compared between conditions using two-way repeated-measures ANOVA (condition and distance factors). Gastrointestinal discomfort was analyzed qualitatively. RESULTS: Compared with placebo (pH 7.37 ± 0.02, [HCO3] 27.5 ± 2.6 mmol·L), the NaHCO3 ingestion resulted in a preexercise blood alkalosis (pH +0.06 ± 0.04, [HCO3] +4.4 ± 2.0 mmol·L, P < 0.05), whereas NH4Cl resulted in a blood acidosis (pH -0.05 ± 0.03, [HCO3] -4.8 ± 2.1 mmol·L, P < 0.05). Anaerobic energy expenditure rate and PO were reduced throughout the trial in NH4Cl compared with placebo and NaHCO3, resulting in a lower total anaerobic work and impaired performance (P < 0.05). Plasma lactate, V˙CO2, and end-tidal CO2 partial pressure were lower and the V˙E/V˙CO2 higher throughout the trial in NH4Cl compared with placebo and NaHCO3 (P < 0.05). There was no difference between NaHCO3 and placebo for any of these variables (P > 0.05). Minimal gastrointestinal distress was noted in all conditions. CONCLUSION: Preexercise acidosis, but not alkalosis, affects anaerobic metabolism and PO during a 4-km cycling TT.