Effect Of Sodium Bicarbonate Ingestion During Altitude Acclimatization On High-altitude, Short-duration, Cycling Performance

Abstract

PURPOSE: Acute altitude exposure induces hyperventilation which, in turn, results in respiratory alkalosis. In an attempt to restore blood pH, the kidneys enhance the rate of bicarbonate excretion which may reduce the buffering capacity of the blood and, thus, the performance in exercises that generate large amounts of lactic acid. Consequently, bicarbonate supplementation during altitude acclimatization may restore the buffering capacity of the blood and enhance exercise performance more so than supplementation at sea level. The purpose of this study, therefore, was to evaluate the effect of sodium bicarbonate ingestion during an 8-hour altitude acclimatization period on subsequent short-duration, high-intensity cycling performance at an altitude of 10,000 ft. METHODS: Following 3 to 5 accommodation trials, four time-trials (TT) were conducted on ten trained males under the following conditions: normobaric/placebo (NPo); normobaric/sodium bicarbonate (NSB); hypobaric/placebo (HPo); and hypobaric/sodium bicarbonate (HSB). All trials were performed in a hypobaric altitude simulator. The TT included completing 360 revolutions as fast as possible on a cycle ergometer at a resistance equal to ≈ 5.5% body weight. RESULTS: The rate of urinary bicarbonate excretion was significantly (p =.005) higher during the hypobaric (1.264 ± 1.05 mg·min-1) versus the normobaric (.324 ±.37 mg·min-1) acclimatization period. Pre- to post-exercise increment in serum lactate concentration was larger (p =.03) by 4.08 ± 2.6 mmol·L-1 in HSB TT compared to HPo TT but the difference between the Normobaric TTs (2.58 ± 1.5 mmol·L-1) was not significant. No significant differences between placebo and SB ingestion trials under both hypobaric and normobaric conditions were found for pre- to post-exercise drop in serum bicarbonate concentration. Additionally, no significant difference was observed between placebo and SB ingestion trials for performance time under normobaric conditions (NPo: 305.0 ± 47.7 sec; NSB: 304.9 ± 44.8 sec) but a significant difference resulted under hypobaric conditions (HPo: 352.5 ± 55.1 sec; HSB: 341.2 ± 58.1 sec; p =.02). CONCLUSIONS: SB ingestion improved cycling performance under hypobaric conditions but not under normobaric conditions.