Superficial cooling does not decrease core body temperature before, during, or after exercise in an American football uniform

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest

Physical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min^-1), and forty-two datasets reported reducing core temperature (-0.002 to -0.070 °C min^-1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of -0.004 °C min^-1 (-0.032 to +0.013 °C min^-1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.

Safety and Efficacy of CarbonCool Half-Body Vest for HAZMAT Decontamination Crews Wearing Personal Protective Equipment: A Pilot Study

BACKGROUND

Personal protective equipment (PPE) are essential for medical personnel responding to hazardous materials (HAZMAT) incidents. However, their impermeable design causes increased physiological strain and reduced thermoregulation, limiting work times and causing heat-related illnesses (HRI). Use of wearable cooling devices slow heat accumulation and have been shown to reduce thermal and cardiovascular strain in such situations.

METHODS

This was a prospective clinical evaluation to determine the tolerability and effectiveness of the CarbonCool cooling system - a half-body cooling vest - in participants undergoing a HAZMAT decontamination recertification. Physiological measurements (heart rate [HR], weight, temperature, and blood pressure) and participant feedback were obtained. The main outcome of interest was participants' tolerability of the cooling vest.

RESULTS

A total of 23 healthy participants were recruited, with 10 randomized to the intervention group and 13 in the control group. Mean age in the control and intervention group was 35.5 years old (SD = 7.8) and 30.0 years old (SD = 6.2), respectively. Qualitative feedback obtained from participants regarding safety, mobility, and cooling efficacy was largely positive. Difference of before-after temperature and HR was 0.3°C (SD = 0.8) and 11.5bpm (SD = 13.6) in the control group compared to 0.0°C (SD = 0.5) and 0.0bpm (SD = 6.4) for the intervention group.

CONCLUSION

This clinical evaluation showed that the CarbonCool cooling vest is safe and tolerable in participants wearing PPE. Further trials with sample size powered to detect physiological outcomes are needed to assess the effect of the cooling vest on a subject's endurance to heat stress.

Thermoregulatory and Perceptual Effects of a Percooling Garment Worn Underneath an American Football Uniform

Keen, ML, Miller, KC, and Zuhl, MN. Thermoregulatory and perceptual effects of a percooling garment worn underneath an American football uniform. J Strength Cond Res 31(11): 2983-2991, 2017-American football athletes are at the highest risk of developing exertional heat illness (EHI). We investigated whether percooling (i.e., cooling during exercise) garments affected perceptual or physiological variables in individuals exercising in the heat while wearing football uniforms. Twelve male participants (age = 24 ± 4 year, mass = 80.1 ± 8.5 kg, height = 182.5 ± 10.4 cm) completed this cross-over, counterbalanced study. On day 1, we measured peak oxygen consumption (V[Combining Dot Above]O2). On days 2 and 3, participants wore percooling garments with (ICE) or without (CON) ice packs over the femoral and brachial arteries. They donned a football uniform and completed 3, 20-minute bouts of treadmill exercise at ∼50% of peak V[Combining Dot Above]O2 (∼33° C, ∼42% relative humidity) followed by a 10-minute rest period. Ice packs were replaced every 20 minutes. Rating of perceived exertion (RPE), thermal sensation, and thirst sensation were measured before and after each exercise bout. Environmental symptoms questionnaire (ESQ) responses and urine specific gravity (Usg) were measured pretesting and after the last exercise bout. V[Combining Dot Above]O2, change in heart rate (ΔHR), and change in rectal temperature (ΔTrec) were measured every 5 minutes. Sweat rate, sweat volume, and percent hypohydration were calculated. No interactions (F17,187 ≤ 1.6, p ≥ 0.1) or main effect of cooling condition (F1,11 ≤ 1.4, p ≥ 0.26) occurred for ΔTrec, ΔHR, thermal sensation, thirst, RPE, ESQ, or Usg. No differences between conditions occurred for sweat volume, sweat rate, or percent hypohydration (t11 ≤ 0.7, p ≥ 0.25). V[Combining Dot Above]O2 differed between conditions over time (F15,165 = 3.3, p < 0.001); ICE was lower than CON at 30, 55, and 70 minutes (p ≤ 0.05). It is unlikely that these garments would prevent EHI or minimize dehydration in football athletes.

Heat-related illness in sports and exercise

Exertional heat-related illness (EHRI) is comprised of several states that afflict physically active persons when exercising during conditions of high environmental heat stress. Certain forms of EHRI may become life threatening if not treated. Exertional heat stroke (EHS), characterized by a core body temperature of >40 ° C and mental status changes, is the most severe form of EHRI. EHS must be treated immediately with rapid body cooling to reduce morbidity and mortality. Many EHRI cases are preventable by following heat acclimatization guidelines, modifying sports and exercise sessions during conditions of high environmental heat stress, maintaining adequate hydration, avoiding exertion in the heat when ill, and by educating sports medicine personnel, coaches, parents, and athletes on the early recognition and prevention of EHRI. Heat exhaustion, exercise-associated collapse, exercise-associated muscle cramps, exercise-associated hyponatremia, and exertional rhabdomyolysis are also described.