Purpose: To determine whether airflow is required to obtain the beneficial effects of rehydration (thermoregulatory and cardiovascular) during exercise in dry heat.
Methods: Ten moderately trained (V˙O2max = 55 ± 8 mL·kg−1·min−1) heat acclimated males pedaled for 60 min at 60% V˙O2max in a hot-dry environment (36 ± 1°C; 29 ± 2% relative humidity) on four different occasions: 1) without rehydration or forced airflow (control trial; CON); 2) rehydrating 100% of sweat losses by ingestion of a 6% carbohydrate-electrolyte solution (rehydration trial; REH); 3) receiving airflow at a velocity of 2.55 m·s−1 (wind trial; WIND); and 4) combining airflow and rehydration (W + R).
Results: Without airflow, rehydration alone (REH) did not lower rectal temperature below CON (39.0 ± 0.1 vs 39.1 ± 0.1°C at 60 min; respectively). However, with airflow, rehydration reduced final rectal temperature (38.8 ± 0.1 vs 38.5 ± 0.1°C; P < 0.05; WIND vs W + R). In the trials with wind (WIND and W + R), skin temperature was reduced by about 0.6°C (P < 0.05), and heart rate drift was prevented. In the trials with rehydration (REH and W + R trials), cardiac output (CO2-rebreathing technique) was maintained higher than CON (16.5 ± 0.4 and 17.0 ± 0.7 vs 15.4 ± 0.4 L·min−1, respectively; P < 0.05).
Conclusion: When exercising in a hot-dry environment, airflow is required for rehydration to improve thermoregulation and cardiovascular function.