Scheduling rest for consecutive light and heavy work loads under hot ambient conditions

Abstract

Three male and three female heat-acclimated subjects participated in a series of five testing sessions aimed at validating a resting period which was assigned to follow work under warm-humid (T_db 36°C, T_wb 31°C) and hot-dry (T_db 50°C, T_wb 25°C) ambient conditions. Each working period consisted of 25 min of walking at 30% [Vdot]_o2max followed by five minutes of carrying a load uphill at 75% [Vdot]_o2max. The working period was based on the expected HR as it could be derived from: (1) the work-specific HR as determined from the linear relationship between % [Vdot]_o2max and HR; (2) the heat-induced increments in HR; and (3) the endurance limits imposed by the age-dependent HR_max. Each 30 min of work was followed by 30 min of rest either under the same ambient conditions as for the working period, or under neutral ambient conditions. Judged by the levelling off of HR and by setting the limits of the T_re rise to 38°C during the consecutive walking periods, only the resting under the neutral conditions proved adequate. The level of blood lactic acid was the same under all ambient conditions for each sex, but was higher for the males, who carried a load of 12 kg, as compared to 10 kg for the females.