Purpose: Investigate the effect of heat stress on postexercise hypotension. Methods: Seven untrained men, aged 21-33 yr, performed two cycling bouts at 60% of oxygen uptake reserve expending 300 kcal in environmental temperatures of 21°C (TEMP) and 35°C (HOT) in a randomized, counter-balanced order. Physiological responses were monitored for 10-min before and 60-min after each exercise bout, and after a non-exercise control session (CON). Blood pressure (BP) also was measured during the subsequent 21-hour recovery period. Results: Compared to CON, systolic and diastolic BPs were significantly reduced in HOT (Δ = -8.3 ± 1.6 and -9.7 ± 1.4 mmHg, P < 0.01) and TEMP (Δ = -4.9 ± 2.1 and -4.5 ± 0.9 mmHg, P < 0.05) during the first 60 min of postexercise recovery. Compared to TEMP, rectal temperature was 0.6 °C higher (P = 0.001), mean skin temperature was 1.8 °C higher (P = 0.013), and plasma volume (PV) was 2.6 percentage points lower (P = 0.005) in HOT. During the subsequent 21-hr recovery period systolic BP was 4.2 mmHg lower in HOT compared to CON (P = 0.016) and 2.5 mmHg lower in HOT compared to TEMP (P = 0.039). Conclusion: Exercise in the heat increases the hypotensive effects of exercise for at least 22 hr in untrained men with elevated blood pressure. Our findings indicate that augmented core and skin temperatures and decreased PV are the main hemodynamic mechanisms underlying a reduction in BP after exercise performed under heat stress.
- baroreceptor reflex; blood pressure; cardiovascular response; energy expenditure; thermoregulation