Exertional heat illness and environmental conditions during a single football season in the southeast

Stressful environmental conditions can present numerous problems for the athletic participant. Exertional heat illness (EHI) is often associated with physical activity in a hot and humid environment; the incidence of EHI is correlated with the rise in ambient air temperature and humidity. 1 Extreme environmental heat places significant stress on the body's ability to perform while thermoregulatory responses are occurring in various internal organs. 2 These responses include mobilizing nutrients and electrolytes and maintaining an appropriate equilibrium of body fluids and increasing body temperature, pH, and blood pressure. If the organ systems do not respond appropriately, the athlete may develop a serious and potentially catastrophic medical condition. From 1979 through 1999, the Centers for Disease Control and Prevention reported 8015 deaths among the general population that were attributable to heat-related illnesses as a result of exposure to excessive heat in the United States. 3 Although most of these fatalities were not sport related, the recent and untimely deaths of several professional, collegiate, and high school athletes as a result of heat-related illnesses have generated national attention related to the risk of exertional heat stress illnesses among athletes. Many professional organizations have published position statements 4–12 regarding the appropriate ways to recognize, treat, and prevent these illnesses. To guard against EHI during athletic events, the American College of Sports Medicine (ACSM) has studied the effects of heat stress and has made specific recommendations (ie, position statements) regarding the participation of individuals in stressful environments. These recommendations consist of guidelines that measure heat stress and define the severity of heat stress by a Wet Bulb Globe Temperature (WBGT) Index. 12 Based on the WBGT at the time of the event, the ACSM also has recommendations regarding the type, duration, and frequency of exercise regimes for a particular day, the frequency of hydration and rest breaks, and whether or not the activity should be moved to a different time of day or canceled altogether. 10 The WBGT Index is the most widely accepted measure of environmental conditions and is used as a monitoring guideline for activities in both athletics and industry. The development of the WBGT equation is well supported by the research performed by Yaglou and Minard 13 and is referenced by many agencies and governing bodies. 3–5, 8, 11, 12, 14–18 The WBGT Index is derived from 3 independent environmental readings: dry bulb temperature (ambient air temperature, dt), wet bulb temperature (humidity, wbt), and black globe temperature (radiant heat, bgt) using the equation below 13: WBGT Index = 0.7wbt + 0.2bgt + 0.1dt Using the WBGT Index score along with published guidelines allows sports medicine professionals to make decisions regarding the intensity, length, time of day, and required rest periods for exercise sessions in hot and humid environments. Since 1975, ACSM has published 3 position statements addressing the prevention of heat illnesses as it applies to distance running. 10, 12, 19 The original statement was updated in 1987 to include thermal injuries affecting not only distance runners but also the general population. 10 In 1996, the ACSM again updated the position statement by addressing exercise in extreme environmental conditions for both the recreational jogging community and elite distance runners, as seen in Table 1. 12 This guideline includes a WBGT Index Risk Chart that delineates temperature ranges and descriptive terminology for potential environmental heat stress. Table 1 American College of Sports Medicine Wet Bulb Globe Temperature Index Risk Chart 5,12* The ACSM Risk Chart recommendations were derived for the general community, recreational joggers, and elite distance runners. These recommendations are to be applied to all geographic areas of the United States and do not take into account sex differences, specific age populations, environmental conditions unique to the different regions of the country, equipment worn during activity, or the size or preexisting level of conditioning or fitness of the athlete. 10 Our purpose was to evaluate the WBGT and the incidence of EHI during American football practice sessions at 5 National Collegiate Athletic Association Division I Southeastern universities from August through October 2003.