The effects of hot-water immersion on cardiovascular and cardiorespiratory health of healthy adults: A systematic review and meta-analysis.

Regular exercise benefits cardiovascular and cardiorespiratory health. Passive heating also induces cardiovascular responses, but its effect on cardiorespiratory fitness remains unclear. Given the overlapping physiological mechanisms between passive heating and exercise, hot-water immersion may serve as an alternative strategy to prevent decline in cardiovascular function and fitness. This systematic review and meta-analysis investigated the effects of hot-water immersion (HWI) on cardiovascular health markers and cardiorespiratory fitness in healthy populations. A comprehensive search of six databases identified 20 studies. The meta-analysis found that a single HWI session significantly increased heart rate (N = 10; mean difference [MD]: 28 bpm, 95% confidence interval [CI]: 19-36.2, p < 0.0001) and decreased diastolic (N = 6; MD: -5 mmHg, 95% CI: -9 to -1, p = 0.015) and mean arterial blood pressure (N = 4; MD: -7 mmHg, 95% CI: -12 to -1, p = 0.03). Repeated immersion reduced resting heart rate (N = 5; MD: -3 bpm, 95% CI: -6 to -1 p = 0.01). No significant effects were observed for other cardiovascular markers, and only one study reported data on cardiorespiratory fitness. Overall, our findings indicate inconclusive beneficial effects of HWI on cardiovascular health markers and further research is needed, especially on cardiorespiratory fitness.