Separate and combined effects of airflow and rehydration during exercise in the heat.

Abstract

To determine whether airflow is required to obtain the beneficial effects of rehydration (thermoregulatory and cardiovascular) during exercise in dry heat. Ten moderately trained (VO2max = 55 +/- 8 mL.kg(-1).min(-1)) heat acclimated males pedaled for 60 min at 60% VO2max in a hot-dry environment (36 +/- 1 degrees 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). Without airflow, rehydration alone (REH) did not lower rectal temperature below CON (39.0 +/- 0.1 vs 39.1 +/- 0.1 degrees C at 60 min; respectively). However, with airflow, rehydration reduced final rectal temperature (38.8 +/- 0.1 vs 38.5 +/- 0.1 degrees 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 degrees 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). When exercising in a hot-dry environment, airflow is required for rehydration to improve thermoregulation and cardiovascular function.