Doctor of Philosophy (PhD)



Document Type



Exercise in the heat increases the risk of dehydration and hyperthermia, subsequently impaired cardiovascular function and increased thermal stress. The purpose of this dissertation is to determine the fluid balance, cardiovascular function, thermoregulation, and cooling intervention during exercise in the heat. Four novel studies were conducted in this dissertation.

The first and second studies investigated the fluid balance during exercise in the heat across different sports with their special concerns. The first study conducted in female soccer, suggesting most players were in a hypohydration state after practice, and various fluid needs were exhibited by different positions, possibly associated with on-field physical exertion characteristics. The second study was a longitudinal study examining the physiological and hematological responses of football players with sickle cell trait (SCT). SCT exhibited ~37% of hemoglobin S and had a greater serum uric acid concentration and red blood cell distribution width. Furthermore, SCT had 14% less distance ran on the field across the same intensity compared to position-matched controls. These two hydration studies provided the applicable information for teams to promote hydration guidelines and better monitor biomarkers in SCT during exercise in the heat.

The third and fourth studies examined the effects of cooling interventions on lowering body temperature and thermal stress. The third study was a pilot study to examine the effects of leg cooling on soccer-simulated intermittent exercise performance. The results suggested leg cooling lowered thigh skin temperature by 4.3°C and was effective to decrease auditory canal temperature, core temperature, and thermal sensation. Tissue saturation index was not changed, suggesting muscle blood flow was not affected in this cooling treatment. The last study determined the effects of t-shirt fabric materials on upper-body heat dissipation during exercise in the heat with or without simulated wind. The results suggested the novel shirt with the cooling fan exhibited a superior upper-body heat dissipation during exercise in the heat, mainly decrease averaged skin temperature, ratings of perceived exertion, and promote subjective overall feeling. Given these two cooling studies above, we provided the noticeable applications in external cooling method and clothing material factor to decrease body thermal stress.

Committee Chair

Johannsen, Neil