Post-exercise hot water immersion enhances haemodynamic and vascular benefits of exercise without further improving cardiorespiratory fitness, glucose, lipids or inflammation.

There is considerable overlap between the mechanisms underlying the health benefits of exercise training and heat therapy. However, it remains unclear whether combining heat therapy with exercise can enhance improvements in cardiovascular and metabolic health. The present study investigated whether post-exercise hot water immersion (EX+HWI) could augment improvements in cardiorespiratory fitness, cardiovascular and metabolic health compared to post-exercise thermoneutral water immersion (EX+TWI). Twenty-four physically inactive middle-aged adults (age: 58 ± 5 years; body mass index: 28 ± 3 kg m- 2; 13 females) were randomly allocated to 8 weeks of supervised EX+HWI (n = 12) or EX+TWI (n = 12). Moderate-intensity aerobic exercise (65-75% maximum heart rate) was performed for 30 min followed by 30 min of immersion at 40°C or 34°C, two to four times per week (total 24 sessions). Cardiorespiratory fitness, brachial artery flow-mediated dilatation, aortic pulse wave velocity, blood pressure and circulating lipids, glucose and inflammatory markers were assessed pre- and post-intervention. Between-group differences showed that EX+HWI resulted in greater reductions in mean arterial pressure (P = 0.029, η2 p = 0.207, mean difference: -4 mmHg) and an increase in brachial artery flow-mediated dilatation (P = 0.030, η2 p = 0.206, 2.33%). In addition, there were greater improvements in perceived physical health (P = 0.036, η2 p = 0.211, 5 a.u.). No between-group differences were observed for cardiorespiratory fitness, aortic stiffness, circulating glucose, lipids and inflammatory markers. Taken together, post-exercise hot water immersion enhances blood pressure and brachial artery endothelial function, in the absence of improvements in cardiorespiratory fitness, circulating glucose, lipids and inflammatory markers. KEY POINTS: Hot water immersion replicates some of the physiological adaptations to exercise, but it is unclear whether post-exercise hot water immersion can augment exercise-derived improvements in cardiovascular health. This is the first study to assess whether 8 weeks of supervised exercise followed by hot water immersion can augment improvements in cardiovascular and metabolic health compared to post-exercise thermoneutral water immersion in physically inactive middle-aged adults. We demonstrate that 30 min of moderate-intensity aerobic exercise, followed by 40°C water immersion, on average three times a week for 8 weeks, reduces diastolic and mean arterial blood pressure more than exercise followed by thermoneutral immersion at 34°C, and increases brachial artery flow-mediated dilatation. These findings provide novel evidence that post-exercise hot water immersion lowers diastolic blood pressure and mean arterial pressure, and improves brachial artery endothelial function, without further enhancing cardiorespiratory fitness, glucose, lipids or inflammation in physically inactive middle-aged adults.