Date of Completion


Embargo Period



Douglas J. Casa, Lawrence E. Armstrong, Yuri Hosokawa, Rebecca L. Stearns

Field of Study



Master of Science

Open Access

Open Access


Exercising in hot and humid conditions is a stressful environment that can be taxing on the human body. In certain situations, uncompensable heat stress may occur in which there is an overwhelming of the thermoregulatory system. This may result in exertional heat illnesses, particularly exertional heat stroke, which warrant rapid and appropriate treatment to avoid long term complications, or even death.

Returning to activity, duty, or play after an exertional heat stroke, or for those who exhibit difficulty exercising in the heat, is a complex process. However, heat tolerance tests have been used, particularly in warriors, as an evaluation tool for assessing return to activity. There are no standard guidelines or protocols of when it is safe for these individuals to return to play.

Therefore, we evaluated a modified heat tolerance test in a cohort of recreational runners to compare physiological responses during a laboratory test and a 7.1-mile outdoor road race. We also aimed to assess patterns in the rise of internal body temperature to determine potential temperature criterion for heat tolerance.

We found that when running at 60% VO2max on a treadmill in an environmental chamber set at 27°C and 50% relative humidity, at least 60 minutes of exercise was necessary to see a plateau in internal body temperature. Additionally, the percentage of body mass loss explained the most variance in temperature rise during the lab and the field protocols.

Major Advisor

Douglas J. Casa