INDUCED ALKALOSIS DOES NOT ATTENUATE THE OXYGEN DRIFT DURING CONSTANT-LOAD EXERCISE 1082

Abstract

Previous investigations have demonstrated an upward drift in oxygen consumption (VO2) during prolonged high intensity exercise. A suggested mechanism for the increase in VO2, given a static power output, is a decrease in blood and muscle pH. The purpose of this study was to determine if induced alkalosis would reduce the magnitude of the oxygen drift during constant-load exercise. Twelve physically active males performed 30 min cycling trials under two experimental conditions, with each condition separated by 7 d. Exercise intensity was equal to the lactate threshold (LT) plus 50% of the difference between the LT and maximal aerobic power (VO2 max). Subjects ingested 0.3 g*kg body wt-1 of either NaHCO3 (BIC) or placebo (PLC) in a randomized counterbalanced order. Arterialized capillary blood samples were collected pre-ingestion, 120 min post-ingestion, and at 10 min, 20 min and 30 min of exercise. Blood samples were analyzed for pH, bicarbonate (HCO3-), base excess (BE), and lactate (La). Expired gas samples were collected continuously and analyzed for VO2 with average values provided every 60 s. The oxygen drift was defined as the change in VO2 from min 3+4 to min 28+29. A repeated measures ANOVA and paired t-tests were used to determine differences between treatments, with p≤0.05. pH, HCO3 and BE were significantly higher for BIC compared to PLC at post-ingestion and throughout exercise. For both BIC and PLC there was a significant increase in VO2 from min 3+4 to min 28+29, however no significant difference was observed between treatments. VO2 values at min 3+4 for BIC and PLC were 28.2±1.6 and 28.8±1.2 mL*kg-1*min-1, respectively. VO2 values at min 28+29 for BIC and PLC were 32.5±1.2 and 32.0±1.3 mL*kg-1*min-1, respectively. In conclusion, while acid-base measures were significantly elevated during the BIC trial, the induced alkalosis did not attenuate the oxygen drift during constantload exercise.