The Impact Of Exercise And Heat Therapy On Overnight Heart Rate Variability

Abstract

Previous research has shown that exercise is an essential lifestyle intervention to improve cardiovascular health and that heat therapy, in the form of hot baths or saunas, may provide numerous cardiovascular health benefits. Purpose: To investigate how combined acute exercise and heat therapy will impact nocturnal heart rate variability, compared to heat therapy or exercise alone in normotensive and hypertensive individuals. We hypothesized that combined exercise and heat therapy will result in a larger decrease in nocturnal heart rate and a larger increase in heart rate variability when compared to heat therapy and exercise tested alone. Methods: This study consisted of three trials in a randomized, counterbalanced order in which six subjects [3 male, 3 female, age 24 ± 6 yr, body mass index (BMI) 30 ± 6] participated in three treatments: exercise alone, heat alone, or exercise and heat combined. Each exercise session consisted of walking on a treadmill for 30 minutes at 60% effort. Each heat therapy session consisted of 45 minutes in a hot (42C) leg bath. The combination session consisted of the exercise trial followed by a heat therapy trial. After each session, subjects ambulatory blood pressure and heart rate variability was taken overnight to assess the outcomes that the interventions had on the subjects. Results: Overnight heart rate significantly decreased following the HT intervention when compared to Ex, ExHT, and baseline measures (Pre: 76 ± 18; Post: 62 ± 14 beats/min); No treatment significantly altered overnight heart rate variability: Ex (Baseline: 68 ± 36; Post: 72 ± 36 ms), ExHT (Baseline: 68 ± 36; Post: 71 ± 34 ms), and HT (Baseline: 68 ± 36; 66 ± 26 ms). Conclusion: Ultimately, exercise alone, heat alone, and exercise and heat combined did not appear to impact the reciprocal balance of sympathetic and parasympathetic dominance assessed by HRV.