Sports Drink Ingestion Inflates Heart Rate Variability: Implications for Pre-training Measures

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Presentation given at National Strength and Conditioning Association National Conference, Washington, D.C.

Sports teams acquire pre-training heart rate variability (HRV) in athletes to assess training status. HHowever, pre-training hydration practices may acutely affect cardiovascular dynamics and thus obscure resting-HRV. This creates a methodological concern for staff because coolers filled with bottles of water and sports drinks are typically made available for athletes in the hours before training. PURPOSE: To determine the effects of 591 ml of cold water and sports drink ingestion on HRV. METHODS: Recreationally-trained, college-age men (n = 6) and women (n = 3) volunteered for this study. On separate days after an overnight fast, subjects ingested 591 ml of water, a sports drink or control (10 ml water) in a randomized order. R-R intervals were recorded for 10 min pre- and for an additional 25 min post-fluid ingestion. Beverages were consumed within a 2-min window. The natural logarithm of the root-mean square of successive R-R intervals (LnRMSSD) was calculated from min 5–10 pre-ingestion to establish baseline (T1) and again at 5–10 min post- (T2) and 20–25 min post-fluid ingestion (T3). A linear mixed model and Cohen’s effect sizes (ES) were used to examine variation in LnRMSSD responses. RESULTS: A significant condition × time interaction was observed (p < 0.0001). LnRMSSD did not change across time for control (T1 = 4.19 ± 0.36, T2 = 4.17 ± 0.39, T3 = 4.27 ± 0.31, p >0.05). LnRMSSD increased following both water (T2 = 4.52 ± 0.26, ES = 1.06) and sports drink (T2 = 4.66 ± 0.38, ES = 1.27) ingestion at T2 (p < 0.05). LnRMSSD remained significantly elevated at T3 for sports drink (T3 = 4.54 ± 0.37, ES = 0.97) relative to control (p < 0.05). Though not statistically significant, ES analysis revealed that LnRMSSD at T2 for the sports drink condition was greater than water (ES = 0.83, p >0.05). In addition, water at T3 (4.49 ± 0.31, ES = 0.64, p >0.05) was greater than control at T3. CONCLUSIONS: Water and sports drink ingestion caused significant increases in LnRMSSD at 5–10 min post-ingestion. The effects persisted to 20-25 min post-ingestion, primarily for the sports drink condition. PRACTICAL APPLICATIONS: Fatigue-related decrements in LnRMSSD may be masked by acute fluid ingestion and thus result in a misinterpretation of training status. For example, elevated HRV typically indicates a positive coping and recovery response to training, reflecting high cardiac-parasympathetic activity. However, the effects of fluid ingestion may produce a false positive by transiently inflating an athletes HRV, masking their true resting-state autonomic activity. Therefore, practitioners should control for fluid ingestion when obtaining HRV measures prior to training. Since LnRMSSD remained above baseline at 25 min post-ingestion, further investigation using extended post-ingestion follow-up is needed to determine how long effects persist.


National Strength and Conditioning Association National Conference


Washington, D.C.