THE CONVECTIVE AFTERDROP COMPONENT DURING HYPOTHERMIC EXERCISE DECREASES WITH DELAYED EXERCISE ONSET

Hypothesis: Following cold water immersion, the post-cooling decrease in esophageal temperature (Tes) (i.e., afterdrop) is 3 times greater d uring exercise than during shivering, presumably due to increased musc ular blood flow and convective core-to-periphery heat loss with exerci se (J. Appl. Physiol. 63:2375, 1987). We felt that if exercise were to commence once the afterdrop period during shivering is complete, the threat of a further decrease in Ter (i.e., a second afterdrop) during the subsequent exercise would be minimized because much of the convect ive capacity for core cooling would already be dissipated. Methods: Si x subjects were each cooled three times in 8 degrees C water, until Te s decreased to 35.3 +/- 0.7 degrees C, and rewarmed by either shiverin g alone, exercise, or exercise commencing once a shivering afterdrop p eriod was complete. Results: The initial afterdrop was greater during Exercise only (1.1 +/- 0.4 degrees C) than Shivering only (0.35 +/- 0. 3 degrees C) and Shivering-Exercise (0.45 +/- 0.2 degrees C) (p < 0.05 ). In contrast, exercise caused a secondary afterdrop of only 0.38 +/- 0.3 degrees C during Shivering-Exercise (p < 0.05). The initial rewar ming rate during Exercise only (3.45 degrees C.h(-1)) was greater than the initial (2.7 degrees C.h(-1)) and second (2.4 degrees C.h(-1)) re warming rates during Shivering-Exercise (p < 0.05), but not significan tly greater than during Shivering only (2.99 degrees C.h(-1)) (p < 0.1 ). Discussion: it is likely that during the Shivering-Exercise protoco l, continued blood flow to shivering muscles: a) contributes to the in itial afterdrop, and thus b) diminishes the convective capacity (or he at sink) available for further cooling during subsequent exercise.