Metabolic and thermoregulatory responses of women to exercise in two thermal environments

Abstract

Seven untrained and unacclimatized female subjects rested, walked for 40 minutes on a treadmill grade at 50% maxV̇o₂, and recovered from exercise under two environmental conditions. The two conditions represented thermal neutrality (T_A = 25°C) and a hot-dry (T_A = 48°C) condition. Thermoregulatory and metabolic measures were assessed. Significantly higher levels of V̇o₂, V̇e, and heart rate occurred during exercise and recovery in 48°C compared to 25°C. Ventilation equivalent and oxygen pulse values suggested reduced metabolic efficiency in the heat. Resting T_re initially decreased in the heat returning to control values within 40 minutes. Comparable changes were not evident during rest in 25°C. The change in T_re occurring with exercise in the heat was double that in the 25°C condition. Body heat content rose 9 kcal/m² during the exercise period in the 25°C environment but was elevated 45 kcal/m² during the walk in the heat. The heat load of the 48°C environment altered thermal balance such that changes in circulatory and respiratory response mechanisms resulted in increased metabolic requirements.