Differential effect of metabolic alkalosis and hypoxia on high-intensity cycling performance

The purpose of this study was to investigate the effects of sodium bicarbonate (NaHCO₃) ingestion and acute hypoxic exposure on repeated bouts of high-intensity cycling to task failure. Twelve subjects completed 4 separate intermittent cycling bouts cycling bouts to task failure (120% peak power output for 30-second interspersed with 30-second active recovery) under the following conditions: normoxia (F_IO₂% at 20.93%) alkalosis (NA), normoxia placebo (NP), hypoxia (F_IO₂% at 14.7%) alkalosis (HA), and hypoxia placebo (HP). For the NA and HA trials, the buffer solution (0.3 g·kg^-1 of NaHCO₃) was dispensed into gelatin capsules and consumed over 90 minutes with 1 L of water. Whole-blood acidbase findings demonstrated metabolic alkalosis in both NA and HA before exercise (HCO₃^-: 32.8 ± 1.8 mmol·L^-1). Time to task failure was significantly impaired in the hypoxic conditions (NA: 199.1 ± 62.3 seconds, NP: 183.8 ± 45.0 seconds, HA: 127.8 ± 27.9 seconds, HP: 133.3 ± 28.7 seconds; p< 0.001; η² = 0.7). There was no difference between the HA and HP conditions (p = 0.41); however the 2 normoxic conditions approached significance with the NA condition on average resulting in approximately 15-second improvement in time to task failure (p = 0.09). These findings suggest that an acute decline in F_IO₂% consistent with hypoxic exposure is more inhibiting than metabolic acidosis during intermittent highintensity cycling to task failure. In application, the use of hypoxia and NaHCO₃ concurrently to improve performance under these conditions does not seem warranted.