The effect of sodium bicarbonate supplementation on the decline in gross efficiency during a 2000-m cycling time trial

Background: Gross efficiency (GE) declines during high-intensity exercise. Increasing extracellular buffer capacity might diminish the decline in GE and thereby improve performance. Purpose: To examine if sodium bicarbonate (NaHCO₃) supplementation diminishes the decline in GE during a 2000-m cycling time trial. Methods: Sixteen male cyclists and 16 female cyclists completed 4 testing sessions including a maximal incremental test, a familiarization trial, and two 2000-m GE tests. The 2000-m GE tests were performed after ingestion of either NaHCO₃ supplements (0.3 g/kg body mass) or placebo supplements (amylum solani, magnesium stearate, and sunflower oil capsules). The GE tests were conducted using a doubleblind, randomized, crossover design. Power output, gas exchange, and time to complete the 2000-m time trials were recorded. Capillary blood samples were analyzed for blood bicarbonate, pH, and lactate concentration. Data were analyzed using magnitude-based inference. Results: The decrement in GE found after the 2000-m time trial was possibly smaller in the male and female groups after NaHCO₃ than with placebo ingestion, with the effect in both groups combined being unclear. The effect on performance was likely trivial for males (placebo 164.2 [5.0] s, NaHCO₃ 164.3 [5.0] s; Δ0.1; ±0.6%), unclear for females (placebo 178.6 [4.8] s, NaHCO₃ 178.0 [4.3] s; Δ-0.3; ±0.5%), and very likely trivial when effects were combined. Blood bicarbonate, pH, and lactate concentration were substantially elevated from rest to pretest after NaHCO3 ingestion. Conclusions: NaHCO₃ supplementation results in an unclear effect on the decrease in GE during high-intensity exercise and in a very likely trivial effect on performance.