Cold-Water Immersion for Hyperthermic Humans Wearing American Football Uniforms

Context: Current treatment recommendations for American football players with exertional heatstroke are to remove clothing and equipment and immerse the body in cold water. It is unknown if wearing a full American football uniform during cold-water immersion (CWI) impairs rectal temperature (T-rec) cooling or exacerbates hypothermic afterdrop. Objective: To determine the time to cool T-rec from 39.5 degrees C to 38.0 degrees C while participants wore a full American football uniform or control uniform during CWI and to determine the uniform's effect on T-rec recovery postimmersion. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: A total of 18 hydrated, physically active, unacclimated men (age = 22 +/- 3 years, height = 178.8 +/- 6.8 cm, mass = 82.3 +/- 12.6 kg, body fat = 13% +/- 4%, body surface area = 2.0 +/- 0.2 m(2)). Intervention(s): Participants wore the control uniform (undergarments, shorts, crew socks, tennis shoes) or full uniform (control plus T-shirt; tennis shoes; jersey; game pants; padding over knees, thighs, and tailbone; helmet; and shoulder pads). They exercised (temperature approximately 40 degrees C, relative humidity approximately 35%) until T-rec reached 39.5 degrees C. They removed their T-shirts and shoes and were then immersed in water (approximately 10 degrees C) while wearing each uniform configuration; time to cool T-rec to 38.0 degrees C (in minutes) was recorded. We measured T-rec (degrees C) every 5 minutes for 30 minutes after immersion. Main Outcome Measure(s): Time to cool from 39.5 degrees C to 38.0 degrees C and T-rec. Results: The T-rec cooled to 38.0 degrees C in 6.19 +/- 2.02 minutes in full uniform and 8.49 +/- 4.78 minutes in control uniform (t(17) = -2.1, P = .03; effect size = 0.48) corresponding to cooling rates of 0.28 degrees C.min(-1) +/- 0.12 degrees C.min(-1) in full uniform and 0.23 degrees C.min(-1) +/- 0.11 degrees C.min(-1) in control uniform (t(17) = 1.6, P = .07, effect size = 0.44). The T-rec postimmersion recovery did not differ between conditions over time (F-1,F-17 = 0.6, P = .59). Conclusions: We speculate that higher skin temperatures before CWI, less shivering, and greater conductive cooling explained the faster cooling in full uniform. Cooling rates were considered ideal when the full uniform was worn during CWI, and wearing the full uniform did not cause a greater postimmersion hypothermic afterdrop. Clinicians may immerse football athletes with hyperthermia wearing a full uniform without concern for negatively affecting body-core cooling.