Ice vest pre-cooling has been show to lower rectal temperature during intermittent exercise in hot conditions but only after 40 min of exercise . The authors suggested that the ice vest may have initiated a strong local cutaneous vasoconstrictor response reducing skin blood flow  and thus the cooling potential, until increases in body temperature and skin blood flow occurred later in exercise. Therefore, the purpose of this study was to determine whether ice vest pre-cooling reduces skin blood flow during intermittent exercise in the heat compared to a no cooling control.
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Price, M., & Maley, M. (2015). The effects of ice vest pre-cooling on skin blood flow at rest and during exercise in the heat. Extreme Physiology and Medicine, 4(Supplement 1), [A127]. https://doi.org/10.1186/2046-7648-4-S1-A127