Thermoregulatory Considerations for Safely Running Long-Distance Races in Hot, Humid Conditions

Abstract

Two male, unacclimitized distance runners, ages 29 and 45, ran on a treadmill at speeds of 176 and 135 m/min, respectively, and 3% grade for 60 min. in eight controlled hot environments. Combinations of five levels of ambient water vapor pressure (15, 18, 23, 26.5 and 29 mm Hg) and four levels of dry-bulb temperature (30.6, 34.2, 37.2 and 40.6°C) in the vicinity of a WBGT line of 28°C were controlled to evaluate their effects on the runners' physiological responses of heart rate, sweat loss, rectal temperature, skin temperatures, respiration rate, and oxygen uptake. The findings indicate that the WBGT index is not adequate as a criterion for evaluating distance runners' responses to heat (i.e., conditions of equal values of WBGT did not produce equivalent physiological responses) and there are conditions beyond the 28°C WBGT line (a recommended guideline) for which acceptable steady-state responses were approached.