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Publication AbstractsThe convective afterdrop component during hypothermic exercise decreases with delayed exercise onsetGiesbrecht GG, Bristow GKAviat Space Environ Med 1998; 69:17-22 AbstractHypothesi: Following cold water immersion, the post-cooling decrease in esophageal temperature (Tes) (i.e., afterdrop) is three times greater during exercise than during shivering, presumably due to increased muscular blood flow and convective core-to-periphery heat loss with exercise (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 Tes (i.e., a second afterdrop) during the subsequent exercise would be minimized because much of the convective capacity for core cooling would already be dissipated. Methods: Six subjects were each cooled three times in 8°C water, until Tes decreased to 35.3 ± 0.7°C, and re-warmed by either shivering alone, exercise, or exercise commencing once a shivering afterdrop period was complete. Results: The initial after drop was greater during Exercise only (1.1 ± 0.4°C) than Shivering only (0.35 ± 0.3°C) and Shivering-Exercise (0.45 ± 0.2°C) (p < 0.05). In contrast, exercise caused a secondary after drop of only 0.38 ± 0.3°C during Shivering-Exercise (p < 0.05). The initial re-warming rate during Exercise only (3.45°C · h-1) was greater than the initial (2.7°C · h-1) and second (2.4°C · h-1) re-warming rates during Shivering-Exercise (p < 0.05), but not significantly greater than during Shivering only (2.99°C · h-1) (p < 0.1). Discussion: It is likely that during the Shivering-Exercise protocol, continued blood flow to shivering muscles: a) contributes to the initial after drop, and thus b) diminishes the convective capacity (or heat sink) available for further cooling during subsequent exercise.
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