Thermoregulatory and metabolic responses to a half-marathon run in hot, humid conditions.

Abstract

This study describes the thermoregulatory and metabolic responses during a simulated half-marathon (21km) run performed outdoors in a hot, humid environment. Ten male runners were recruited for the study, The run was carried out individually under solar radiation on a predetermined path in the following environmental conditions (ambient temperature: 27.96±1.70°C, globe temperature: 28.52±2.51°C, relative humidity: 76.88±7.49%, wet bulb globe temperature: 25.80±1.18°C). Core temperature, skin temperature, head temperature, heat storage, heart rate, expired gases, rating of perceived exertion, and speed were measured or calculated before the start, every 3km, and immediately following the run. Comparisons were made for each dependent variable using one-way repeated measures analysis of variance tests, and a Bonferroni test. Average run time and pace were 101:00±9:52min and 4:48±00:16minkm-1, respectively. Participants significantly reduced their running speed, oxygen consumption, and heat storage at 9km (p<0.05). While core temperature was significantly increased at 6km (p<0.05) before plateauing for the remainder of the run. The key finding was that most of the runners reduced their pace when a Tcore of 39°C was reached which occurred between 6 and 9km of the run, yet runners were able to increase their speed demonstrating an "end-spurt" near the end of the run.