Changes in cardiac function before and after hot water immersion and endurance exercise in middle-aged individuals with overweight or obesity

PURPOSE: We investigated the acute effects of ecologically valid hot water immersion (HWI) and endurance exercise (END) interventions on indices of left (LV) and right ventricular (RV) function in middle-aged individuals with overweight or obesity. METHODS: Twenty-five (15♀, 10♂) individuals were recruited. A single session of HWI (40 °C for 30 min with the water level at the sternum) and END (cycling 30 min at 60-70% of max heart rate [HR]) were carried out in randomised order, separated by at least 72 h. Core body temperature (Tc) and HR were monitored throughout each session. Blood pressure and ventricular parameters, including LV global longitudinal strain (LV GLS) and tricuspid annular plane systolic excursion (TAPSE), were assessed before and after each session. RESULTS: A significant increase in Tc was greater after HWI (Δ0.91 ± 0.32 °C) than END (Δ0.72 ± 0.29 °C; interaction: p = 0.004). Similarly, HR increased more after HWI than END (Δ33 ± 14 vs. Δ25 ± 12 bpm; p = 0.042) and HWI induced greater reductions in post-intervention SBP (Δ-5.7 ± 10.0 vs. Δ0.6 ± 6.6 mmHg; p = 0.019) and DBP (Δ-9.2 ± 9.2 vs. Δ-1.5 ± 5.1 mmHg; p = 0.001). There was a greater increase in LV GLS following HWI (Δ-2.5 ± 2.3%) compared to END (Δ-0.76 ± 2.09%; p = 0.008) and a significant increase in TAPSE after HWI (Δ3.95 ± 4.32 mm; p < 0.001). CONCLUSION: We observed greater increases in Tc, HR, and post-exercise LV and RV function following a HWI intervention compared to acute END. The physiological and practical importance of these differences should be explored further in long-term chronic programs in populations that could benefit from an alternative to the traditional END for cardiovascular benefits.