Effect Of Beverage Consumption On Cardiovascular And Resting Metabolic Responses To Post-exercise Dehydration

Commercially-available sports drinks (CES) are commonly consumed to aid post-exercise rehydration; however, their effects on autonomic function, metabolic rate, and substrate use are not well established. PURPOSE: To compare the effects of CES and water (PLA) on resting heart rate variability (HRV) and metabolism during post-exercise rehydration. METHODS: Sixteen healthy participants (6 female) cycled in the heat (35oC, 40% RH) to induce dehydration equal to 2% of body weight (BW). In a randomised crossover design, participants were assigned either CES or PLA to replace 150% of weight loss over a 30-minute period. Baseline resting metabolic rate (RMR) and HRV were assessed at a screening visit. Plasma glucose, RMR, and HRV were measured post-dehydration, and 60-, 120-, and 180-min post-rehydration and analyzed using a mixed model consisting of treatment (PLA vs CES), time, and their interaction. RESULTS: Mean dehydration (-1.80 ± 0.43% BW) and breathing rate during HRV analysis (16.4 ± 3.2 breaths/min) did not differ between trials (p > 0.54). Effects of time (p = 0.01), treatment (p = 0.05), and treatment*time interaction (p = 0.05) were found for low-frequency/high-frequency power (LF/HF) ratio due to an increased LF/HF post-dehydration that remained elevated at 60- (p = 0.01) and 120-post-rehydration (p = 0.01) in CES, but not PLA. Decreased HF and increased LF was observed post-dehydration compared to baseline (p < 0.01). A treatment*time interaction was found for HF and LF, with lower HF (45.9 ± 19.8 vs 54.8 ± 14.6 nU, p < 0.05) and greater LF (54.1 ± 19.8 vs 45.1 ± 14.6 nU, p < 0.05) in CES at 120-post-rehydration compared to PLA. Plasma glucose was elevated with CES throughout the 30 minute post-rehydration period compared to PLA (all p < 0.05). Total energy expenditure (EE; kcal/L O2) remained depressed at 180-min post-PLA ingestion but increased 60-min post-rehydration with CES and decreased back to baseline values by 180-min post-rehydration (all p < 0.05). Lower fat and higher carbohydrate oxidation was observed in CES compared to PLA during post-rehydration measurements (p < 0.01 for both). CONCLUSION: Post-exercise rehydration with CES may augment sympathetic activity and EE due to glucose effects. The depressed state in PLA could represent continued fatigue and energy conservation due to substrate availability.