Interaction Between Exercise Intensity And Burn Size Affects Body Temperature During Exercise In The Heat

Abstract

US Army Standards of Medical Fitness exclude personnel who have sustained burn injuries covering 40% or more of their body surface area (BSA). However, this requirement is not specific to different exercise intensities that an individual is expected to perform and therefore does not take metabolic heat generation into account. PURPOSE: To test the hypothesis that the magnitude of the elevation in internal body temperature during exercise in a warm environment is influenced by the combination of exercise intensity and percentage BSA burned. METHODS: Nine healthy participants (8 males, 1 female; 33±9 y; 176±7 cm, 75.2±12.0 kg) completed eight exercise trials on a cycle ergometer, each with differing combinations of exercise intensities (Low: 4 W/kg and Moderate: 6 W/kg) and simulated BSA burn percentages in a warm environmental chamber (39.8±0.3°C, 20.5±1.5 %rh). Burns were simulated by covering 0%, 20%, 40% or 60% of participants’ BSA with a highly absorbent, vapor-impermeable material. Gastrointestinal temperature (TGI) was recorded throughout exercise, with the primary analysis (mixed-model with contrasts and Bonferroni corrections comparing simulated burn trials to 0%, with p<0.017 for significance) being the magnitude of the elevation in TGI after 60 min of exercise. RESULTS: The statistical model identified an interaction effect (p=0.005), suggesting that the magnitude of the elevation in TGI was influenced by both exercise intensity and simulated BSA. Regardless of the percentage BSA burn simulated, the increase in TGI was similar across low intensity trials (mean increase: 0.69±0.27°C, p>0.05), However, during moderate intensity exercise the magnitude of the increase in TGI was greater for the 60% (1.76±0.39°C; p<0.001) and 40% (1.23±0.51°C; p=0.0014) BSA coverage trials, relative to the 0% (0.80±0.42°C) BSA coverage trial. There were no differences between 0% and 20% (1.06±0.42°C; p=0.049) BSA coverage trials. CONCLUSIONS: These data suggest that exercise intensity influences the relationship between burn injury size and thermoregulatory responses during exercise in a warm environment. Clinical guidance and US Army Standards for burn survivors should, therefore, consider the intensity of the exercise bout alongside BSA burned when determining limitations to physical activity.