The Effects Of Hydration Status On Heart Rate Variability Following Heavy Intensity Resistance Exercise

Heart rate variability (HRV) is a non-invasive method used to monitor physiological stress via assessment of sympathetic and parasympathetic regulations and can indicate an individual’s recovery and readiness to exercise. Evidence suggests that dehydration negatively impacts HRV; however, the influence of hydration status on HRV following heavy resistance exercise (RE) is unknown. PURPOSE: To investigate the effect of hydration status on HRV indices following heavy intensity RE. METHODS: 14 resistance-trained men (age, 21 ± 2 years; height, 176.25 ± 5.84 cm; weight, 81.31 ± 12.77 kg) participated in this study. In a randomized, counterbalanced order, participants performed a heavy-intensity RE protocol in a euhydrated (EUH; urine specific gravity [USG] < 1.020) and a dehydrated (DEH; USG > 1.020) state, with conditions separated by 2-weeks. HRV indices (standard deviation of normal sinus beats [SDNN], root mean square of successive differences between normal heartbeats [RMSSD], high frequency power [HF], low frequency power [LF], LF:HF ratio, standard deviation of Poincaré plot perpendicular to [SD1] and along the line of identity [SD2]) were measured with participants lying in a supine position for 5 mins in a dark room at baseline, immediately post-, 1 hr-, 2 hr-, and 3 hr post-RE. Repeated measure analysis of variance was used to determine the effect of hydration status on HRV indices at each timepoint, with Bonferroni corrections for post-hoc analysis. RESULTS: RMSSD was significantly higher 1 hr post-exercise in EUH (30.69 ± 7.09 ms) compared to DEH (16.31 ± 2.44 ms; p = 0.04). Similarly, HF power was significantly higher 1 hr post-exercise in EUH (32.49 ± 4.12%) compared to DEH (16.63 ± 2.71%; p < 0.01). In contrast, LF power was lower 1 hr post-exercise in EUH (57.74 ± 3.62%) compared to DEH (75.95 ± 3.42%; p = 0.02), with LF:HF ratio significantly lower in EUH (2.36 ± 0.62) than DEH (6.21 ± 1.34; p = 0.01). SD1 was significantly greater 1 hr post-exercise in EUH (21.74 ± 5.03 ms) than DEH (11.54 ± 1.73 ms; p = 0.04). No significant condition x time effects were observed for SDNN and SD2, or at remaining timepoints. CONCLUSION: These findings indicate that recovery and readiness to exercise are impaired 1 hr following heavy intensity RE in a dehydrated state. However, impairments were ameliorated 2-3 hrs proceeding the RE bout.