Physiologic and perceptual responses to cold-shower cooling after exercise-induced hyperthermia

Context: Exercise conducted in hot, humid environments increases the risk for exertional heat stroke (EHS). The current recommended treatment of EHS is cold-water immersion; however, limitations may require the use of alternative resources such as a cold shower (CS) or dousing with a hose to cool EHS patients. Objective: To investigate the cooling effectiveness of a CS after exercise-induced hyperthermia. Design: Randomized, crossover controlled study. Setting: Environmental chamber (temperature = 33.4 ° C ± 2.1 ° C; relative humidity = 27.1% ± 1.4%). Patients or Other Participants: Seventeen participants (10 male, 7 female; height=1.75 ± 0.07 m, body mass=70.4 ± 8.7 kg, body surface area = 1.85 ± 0.13 m², age range = 19-35 years) volunteered. Intervention(s): On 2 occasions, participants completed matched-intensity volitional exercise on an ergometer or treadmill to elevate rectal temperature to ≥ 39°C or until participant fatigue prevented continuation (reaching at least 38.5°C). They were then either treated with a CS (20.8°C ± 0.80°C) or seated in the chamber (control [CON] condition) for 15 minutes. Main Outcome Measure(s): Rectal temperature, calculated cooling rate, heart rate, and perceptual measures (thermal sensation and perceived muscle pain). Results: The rectal temperature (P=.98), heart rate (P=.85), thermal sensation (P = .69), and muscle pain (P = .31) were not different during exercise for the CS and CON trials (P > .05). Overall, the cooling rate was faster during CS (0.07°C/min ± 0.03 ° C/min) than during CON (0.04 ° C/min ± 0.03 ° C/min; t₁₆ = 2.77, P=.01). Heart-rate changes were greater during CS (45 ± 20 beats per minute) compared with CON (27 ± 10 beats per minute; t₁₆=3.32, P=.004). Thermal sensation was reduced to a greater extent with CS than with CON (F_3,45= 41.12, P < .001). Conclusions: Ahough the CS facilitated cooling rates faster than no treatment, clinicians should continue to advocate for accepted cooling modalities and use CS only if no other validated means of cooling are available.