School of Rehabilitation and Medical Sciences, Central Michigan University, Mount Pleasant.
J Athl Train. 2019 Jul;54(7):758-764. doi: 10.4085/1062-6050-175-18. Epub 2019 Jul 25.
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?
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 (T) 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?
Crossover study.
Laboratory.
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 T was 39.5°C. While wearing equipment, they then underwent CWI until T 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 T to calculate cooling rates.
Precooling allowed participants to exercise 17.6 ± 3.6 minutes longer before reaching 39.5°C ( = 17.0, < .001). Precooling did not affect postexercise CWI T cooling rates (PC = 0.18°C/min ± 0.06°C/min, control = 0.20°C/min ± 0.09°C/min; = 0.9, = .17); ESQ responses ( = 1.3, = .3); or RPE ( = 2.9, = .07). Precooling temporarily lowered thermal sensation ( = 21.7, < .001) and heart rate ( = 21.0, < .001) during exercise.
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).
运动性中暑是导致美式足球运动员死亡的主要原因之一。全身冷水浸泡（CWI）预冷（PC）可能预防严重的体温过高，并可能预防运动性中暑。然而，当参与者在热环境中穿着美式足球制服进行运动时，尚不清楚 PC 会在多快的时间内导致参与者出现严重的体温过高。PC 是否会改变参与者体温过高时 CWI 的效果，或者是否会影响运动过程中的感知变量？
我们提出了 3 个问题：（1）PC 是否会影响参与者在热环境中运动时体温升高的速度？（2）运动前的 PC 是否会影响参与者体温过高时的直肠温度（T）冷却速率？（3）PC 是否会影响感知变量，如感觉用力程度（RPE）、热感觉和环境症状问卷（ESQ）的反应？
交叉研究。
实验室。
12 名身体活跃的男性（年龄=24±4 岁，身高=181.8±8.4cm，体重=79.9±10.3kg）。
在 PC 日，参与者完成 15 分钟的 CWI（9.98°C±0.04°C）。他们穿着美式足球制服在热环境中（温度=39.1°C±0.3°C，相对湿度=36%±2%）运动，直到 T 达到 39.5°C。在穿着装备的同时，他们进行 CWI，直到 T 达到 38°C。对照日的程序与 PC 干预相同，只是没有 PC。
直肠温度、心率、热感觉、RPE 和 ESQ 反应在整个测试过程中都进行了测量。冷水浸泡的持续时间与 T 一起用于计算冷却速率。
PC 使参与者在达到 39.5°C 之前多运动了 17.6±3.6 分钟（ = 17.0， <.001）。PC 不影响运动后 CWI 的 T 冷却速率（PC=0.18°C/min±0.06°C/min，对照=0.20°C/min±0.09°C/min； = 0.9， =.17）；ESQ 反应（ = 1.3， =.3）；或 RPE（ = 2.9， =.07）。PC 在运动过程中暂时降低了热感觉（ = 21.7， <.001）和心率（ = 21.0， <.001）。
由于 PC 延迟了体温过高，而没有对感知变量或 CWI 效果产生负面影响，临床医生可能会考虑实施 PC 与其他预防热相关疾病的已证实策略一起使用（例如，适应）。
