Water intake accelerates post-exercise cardiac vagal reactivation in humans

Post-exercise cardiac vagal reactivation is well-investigated; however, the effect of water intake during this period has not been well studied. Therefore, our aim was to assess the influence of water intake on the cardiac vagal reactivation after 30 min of a submaximal cycling exercise. Ten healthy subjects (eight men) aged 23-35 years were evaluated. A 3-day testing cycle duration, subjects were randomly chosen to drink either 500 ml (experimental visit) or 50 ml (control visit) of water immediately after the 30-min cycling exercise at a workload representing 80% of a previously measured anaerobic threshold. A cardiac vagal index (CVI) was obtained using the 4-s exercise test measured before and after (10 and 30 min) exercise at each testing day. Data analysis (2 x 3 ANOVA for repeated measures) showed higher cardiac vagal activity at the 30-min post-exercise period when 500 ml of water was ingested. CVI values for the 500 and 50 ml trials were 1.55 +/- 0.04 vs. 1.49 +/- 0.04, P = 0.003 (mean +/- SEM), respectively. Heart rate and blood pressure values were relatively the same. In conclusion, water intake of about 500 ml immediately after 30 min of cycling exercise accelerates post-exercise cardiac vagal reactivation. These results suggest that post-exercise hydration might be beneficial not only for thermoregulation, but also for vagal reactivation.