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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 ( 4.66 ± 0.62 l min−1) before and to 90 min after cycling at 60% 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 (Δ 0.41 ± 0.17 l min−1; P= 0.027), systemic vascular conductance (Δ 6.0 ± 2.2 ml min−1 mmHg−1; P= 0.001) and stroke volume (Δ 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.