Fluid replacement and heat stress during exercise alter post‐exercise cardiac haemodynamics in endurance exercise‐trained men

It has been reported that endurance exercise-trained men have decreases in cardiac output with no change in systemic vascular conductance during post-exercise hypotension, which differs from sedentary and normally active populations. As inadequate hydration may explain these differences, we tested the hypothesis that fluid replacement prevents this post-exercise fall in cardiac output, and further, exercise in a warm environment would cause greater decreases in cardiac output. We studied 14 trained men (VO2,peak 4.66 +/- 0.62 l min(-1)) before and to 90 min after cycling at 60% VO2,peak for 60 min under three conditions: Control (no water was consumed during exercise in a thermoneutral environment), Fluid (water was consumed to match sweat loss during exercise in a thermoneutral environment) and Warm (no water was consumed during exercise in a warm environment). Arterial pressure and cardiac output were measured pre- and post-exercise in a thermoneutral environment. The fall in mean arterial pressure following exercise was not different between conditions (P = 0.453). Higher post-exercise cardiac output (Delta 0.41 +/- 0.17 l min(-1); P = 0.027), systemic vascular conductance (Delta 6.0 +/- 2.2 ml min(-1) mmHg(-1); P = 0.001) and stroke volume (Delta 9.1 +/- 2.1 ml beat(-1); P < 0.001) were seen in Fluid compared to Control, but there was no difference between Fluid and Warm (all P > 0.05). These data suggest that fluid replacement mitigates the post-exercise decrease in cardiac output in endurance-exercise trained men. Surprisingly, exercise in a warm environment also mitigates the post-exercise fall in cardiac output.