Dehydration reduces heart rate variability in recreationally resistance-trained men

BACKGROUND: Optimizing hydration strategies is essential for athletic recovery, yet over 50% of athletes arrive at training dehydrated. Heart rate variability (HRV) assesses recovery and could be influenced by hydration status and resistance exercise (RE). This study investigated the effects of pre-RE hydration status on HRV up to 3 hours following RE. METHODS: Twelve recreationally resistance-trained men (mean±SD; age: 21±2 years; weight: 81.3±12.8 kg; height: 176.3±5.8 cm) completed 5 sets of 10 repetitions of bilateral leg press and knee extension at 80% of 1RM. Participants performed resistance exercise while euhydrated (EUH) or dehydrated (DEH) in a randomized order, indicated by a urine specific gravity of <1.020 and ≥1.020, respectively. HRV was assessed pre-RE, immediately post-RE, and hourly for 3 hours post-RE. Linear mixed-effects models assessed differences in HRV parameters between hydration conditions. RESULTS: Independent of time, dehydration significantly reduced HF power (DEH: 27.4±18.2%; EUH: 33.0±18.6%, P<0.01, d=0.30) and increased LF power (DEH: 61.7±15.6%; EUH: 56.3±14.8%, P<0.05, d=0.36) and LF/HF ratio (DEH: 4.5±4.3; EUH: 2.8±2.3, P<0.01, d=0.49) compared to euhydration. CONCLUSIONS: Overall, the results indicate that dehydration increases sympathetic activity and reduces parasympathetic activity, reducing HRV. These results provide implications for optimizing recovery status in athletes.