Then they ran at approximately 90% of their age-predicted maximum HR for 2 minutes. ![]() For the first 3 minutes of each 5-minute bout, participants walked on a treadmill (model 1850 Proform Performance, Logan, UT) at 4.8 km/h (3 mph). Participants completed successive 5-minute exercise bouts with no rest between bouts until T rec reached 39.5☌. ![]() Therefore, before clinicians can recommend PC as an EHI-prevention strategy for American football players, clarity is needed as to whether PC affects perceptual variables related to EHI (eg, thermal sensation, environmental symptoms questionnaire responses) and CWI rectal temperature (T rec) cooling rates after participants become hyperthermic. Finally, some of these effects (eg, delayed sweating, cutaneous vasoconstriction, increased H S) could alter body heat transfer, which could modify CWI cooling rates if an athlete needed emergency cooling. 13, 14 Perceptually, PC could alter thermal comfort and thermal sensation before exercise, which may affect how hot an athlete feels during exercise or lead to the underreporting of EHI symptoms or signs (or both). ![]() For example, PC can induce vasoconstriction of cutaneous blood vessels, reduce sweat rate and skin temperature, and delay the onset of sweating by reducing body core temperature. 12 However, PC may have other physiological effects that could predispose athletes to EHI. Precooling reduces body core temperature and improves body heat storage (H S) capacity, 8– 10 enhances core-to-skin temperature gradients, 11 and delays the onset of hyperthermia-induced fatigue. 7 Lowering body core temperature before exercise, termed precooling (PC), with whole-body cold-water immersion (CWI) may also be an effective strategy to prevent EHS or severe hyperthermia. Current EHS-prevention strategies include gradual heat acclimatization over the course of 7 to 14 days, maintaining adequate hydration during physical activity, incorporating proper work : rest ratios for exercise in the heat, and emergency preparedness.
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