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Bradley, LJ, Miller, KC, Wiese, BW, and Novak, JR. Precooling's effect on American football skills. J Strength Cond Res 33(10): 2616-2621, 2019-Precooling (i.e. cooling before exercise) may reduce the risk of exertional heatstroke (EHS) in American football athletes. However, implementation of precooling by coaches or medical staff would likely be poor if it impaired performance. We investigated whether precooling impacted American football skill performance in this randomized, crossover, counterbalanced study. Twelve men (24 +/- 2 years, mass = 85.5 +/- 6.3 kg, height = 181.8 +/- 8.1 cm) completed a familiarization day to practice each skill and then 2 testing days. On testing days (wet-bulb globe temperature = 19.3 +/- 4.1[degrees] C), subjects were either precooled for 15 minutes using cold-water immersion (10.1 +/- 0.3[degrees] C) or not (control). Then, they donned an American football uniform and completed several bouts of 8 different football skills. Rectal temperature (Trec) was measured before, during, and after skill testing. Precooling did not affect vertical jump, broad jump, agility, dynamic or stationary catching, or maximum throwing distance (p >= 0.13). Precooling impaired 40-yard dash time (precooling = 5.72 +/- 0.53 seconds, control = 5.31 +/- 0.34 seconds; p = 0.03, effect size = 1.2) and throwing accuracy (precooling = 4 +/- 1 points, control = 7 +/- 2 points; p = 0.001, effect size = 1.4). On average, Trec was 0.58 +/- 0.35[degrees] C lower during skills testing after precooling and statistically differed from control from minute 10 to the end of testing (~35 minutes; p < 0.05, effect size >= 1.2). Precooling may be a useful EHS prevention strategy in American football players because it lowered Trec without impacting most skills. By lowering Trec, precooling would prolong the time it would take for an athlete's Trec to become dangerous (i.e. >40.5[degrees] C). If precooling is implemented, coaches should alter practice so that throwing accuracy and speed drills occur after an athlete's Trec returns to normal (i.e. >35 minutes). [ABSTRACT FROM AUTHOR]

Context Exertional heatstroke is one of the leading causes of death in American football players. Precooling (PC) with whole-body cold-water immersion (CWI) may prevent severe hyperthermia and, possibly, exertional heatstroke. However, it is unknown how much PC delays severe hyperthermia when participants wear American football uniforms during exercise in the heat. Does PC alter the effectiveness of CWI once participants become hyperthermic or affect perceptual variables during exercise? Objectives We asked 3 questions: (1) Does PC affect how quickly participants become hyperthermic during exercise in the heat? (2) Does PC before exercise affect rectal temperature (Trec) cooling rates once participants become hyperthermic? (3) Does PC affect perceptual variables such as rating of perceived exertion (RPE), thermal sensation, and environmental symptoms questionnaire (ESQ) responses? Design Crossover study. Setting Laboratory. Patients or Other Participants Twelve physically active males (age = 24 ± 4 years, height = 181.8 ± 8.4 cm, mass = 79.9 ± 10.3 kg). Intervention(s) On PC days, participants completed 15 minutes of CWI (9.98°C ± 0.04°C). They donned American football uniforms and exercised in the heat (temperature = 39.1°C ± 0.3°C, relative humidity = 36% ± 2%) until Trec was 39.5°C. While wearing equipment, they then underwent CWI until Trec was 38°C. Control-day procedures were the same except for the PC intervention. Main Outcome Measure(s) Rectal temperature, heart rate, thermal sensation, RPE, and ESQ responses were measured throughout testing. The duration of cold-water immersion was used in conjunction with Trec to calculate cooling rates. Results Precooling allowed participants to exercise 17.6 ± 3.6 minutes longer before reaching 39.5°C (t11 = 17.0, P < .001). Precooling did not affect postexercise CWI Trec cooling rates (PC = 0.18°C/min ± 0.06°C/min, control = 0.20°C/min ± 0.09°C/min; t11 = 0.9, P = .17); ESQ responses (F2,24 = 1.3, P = .3); or RPE (F2,22 = 2.9, P = .07). Precooling temporarily lowered thermal sensation (F3,26 = 21.7, P < .001) and heart rate (F3,29 = 21.0, P < .001) during exercise. Conclusions Because PC delayed hyperthermia without negatively affecting perceptual variables or CWI effectiveness, clinicians may consider implementing PC along with other proven strategies for preventing heat illness (eg, acclimatization). [ABSTRACT FROM AUTHOR]

Context: Treatment delays can be contributing factors in the deaths of American football athletes from exertional heat stroke. Ideally, clinicians begin cold-water immersion (CWI) to reduce rectal temperature (T rec ) to <38.9°C within 30 minutes of collapse. If delays occur, experts recommend T rec cooling rates that exceed 0.15°C/min. Whether treatment delays affect CWI cooling rates or perceptual variables when football uniforms are worn is unknown., Objective: To answer 3 questions: (1) Does wearing a football uniform and delaying CWI by 5 minutes or 30 minutes affect T rec cooling rates? (2) Do T rec cooling rates exceed 0.15°C/min when treatment delays have occurred and individuals wear football uniforms during CWI? (3) How do treatment delays affect thermal sensation and Environmental Symptoms Questionnaire responses?, Design: Crossover study., Setting: Laboratory., Patients or Other Participants: Ten physically active men (age = 22 ± 2 y, height = 183.0 ± 6.9 cm, mass = 78.9 ± 6.0 kg)., Intervention(s): On 2 days, participants wore American football uniforms and exercised in the heat until T rec was 39.75°C. Then they sat in the heat, with equipment on, for either 5 or 30 minutes before undergoing CWI (10.6°C ± 0.1°C) until T rec reached 37.75°C., Main Outcome Measure(s): Rectal temperature and CWI duration were used to calculate cooling rates. Thermal sensation was measured pre-exercise, postexercise, postdelay, and post-CWI. Responses to the Environmental Symptoms Questionnaire were obtained pre-exercise, postdelay, and post-CWI., Results: The T rec cooling rates exceeded recommendations and were unaffected by treatment delays (5-minute delay = 0.20°C/min ± 0.07°C/min, 30-minute delay = 0.19°C/min ± 0.05°C/min; P = .4). Thermal sensation differed between conditions only postdelay (5-minute delay = 6.5 ± 0.6, 30-minute delay = 5.5 ± 0.7; P < .05). Environmental Symptoms Questionnaire responses differed between conditions only postdelay (5-minute delay = 27 ± 15, 30-minute delay = 16 ± 12; P < .05)., Conclusions: Treatment delays and football equipment did not impair CWI's effectiveness. Because participants felt cooler and better after the 30-minute delay despite still having elevated T rec , clinicians should use objective measurements (eg, T rec ) to guide their decision making for patients with possible exertional heat stroke.