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Health and Human Physiological Sciences

Hemostatic and Inflammatory Responses to Exercise Induced Heat Stress in Normally Trained Males

Melanie A. Cyr, Alexandra G. Harding, Anne Ledyard, Mikayla R. Nemes

Dr. Denise L. Smith


The purpose of this study is to examine the hemostatic and inflammatory responses to an acute bout of exercise in the heat as compared to in thermoneutral conditions in normally trained males.

Nine healthy normally trained men reported between 6:30 and 9:30am and cycled at 60%VO2max for 30 min on two occasions; one exercise bout was in a thermoneutral (TN) condition and the other was in heat stressed (HS) condition, with the order randomly assigned. Blood was drawn from the antecubital vein before exercise following five minutes rest on the cycle ergometer, and also immediately post-exercise.

Fibrinogen levels increased during exercise with no difference between conditions. Plasminogen activator inhibitor (PAI-1) increased significantly with exercise in the heat, but did not change significantly in the TN condition. There was no significant main effect for time or condition on platelet function, prothrombin time (PT), or activated partial thromboplastin time (aPTT). Cell adhesion molecules did not change significantly during exercise in either the HS or TN condition, despite a strong trend for a significant time effect. The cytokine response showed no changes during exercise and no significant differences between conditions for both interleukin-10 (IL-10) and tumor necrosis factor-a (TNF-a).

The activation or depression of coagulation, fibrinolysis, and inflammation varies between a thermoneutral and heat stress exercise condition, and over time. During exercise induced heat stress, coagulation activity increased, fibrinolysis decreased, and there was no change in PT, aPTT, platelet function, sVCAM-1 concentration, as well as no change in IL-10 or TNF-?. In the thermoneutral environment there was an increase in clotting activity, no change in, and no change in sVCAM-1 concentration, PT, aPTT, platelet function, or the inflammatory response. The reported increase in fibrinogen concentration in both conditions, but an increase in PAI-1 only in the heat, suggests increased clotting activity during exercise performed in the heat. This imbalance between clotting and fibrinolysis is the pathogenesis for cardiovascular events, and requires further investigation.