Active Voice: Revisiting Dangers of Football Practice in the Dog Days of Summer
By Lacy A. Holowatz, Ph.D.
Lacy A. Holowatz, Ph.D., is Assistant Professor of Kinesiology at Penn State University in University Park, Pennsylvania. She utilizes in vivo and in vitro approaches using human cutaneous circulation to examine the underlying signaling mechanisms mediating microvascular dysfunction with primary human aging, hypercholesterolemia and essential hypertension. This is the first of two articles appearing in consecutive issues of SMB that addresses the serious hazard of sports training and competition under conditions of high environmental temperatures. This contribution by Dr. Holowatz addresses physiological issues that increase risk of hyperthermia injury to athletes, a particular concern for the many young athletes around the U.S. who have recently started football practice. The second article, to appear next week from Dr. Scott Pyne, will focus on recommendations for prevention and management of heat-related exercise injuries on the field.
This summer, the majority of the U.S. has experienced prolonged periods of high environmental temperatures and high humidity. As humans, we have the ability to thermoregulate to maintain body temperature within narrow limits during exercise and exposure to heat. However, as of the beginning of August, two heat-related deaths in high school football players have occurred along with the collapse and untimely death of an assistant coach. Therefore, with two-a-day football practices taking place for both college and high school athletes, it is important to understand the physiological issues, dangers, preventative strategies and important safety recommendations to keep athletes safe.
During exercise in the heat, the cardiovascular system works to supply blood to the exercising muscles for metabolism. This generates a great deal of heat, and in order to dissipate that heat, blood flow to the skin increases for thermoregulation. Blood flowing to the skin helps to support sweating, which cools the skin and the blood flowing back to the body’s core. However, high environmental humidity coupled with the use of protective clothing (i.e. football pads) limits the body’s ability to evaporate sweat and cool the body. Further, if ambient temperature exceeds skin temperature, additional heat can be gained from the environment. For football, the combination of high-intensity workouts, multiple workouts over consecutive days and protective equipment (which reduces ventilation and evaporation of sweat) can result in a deadly combination.
Heat-related illness in athletic populations occurs with the combination of prolonged exercise (many hours and multiple practices) and excessive sweating. Over a period of time without adequate replacement, the fluids lost from sweating cause further stress on the cardiovascular system and dangerously high body temperatures. The most sensitive and vulnerable to high body temperature is the brain. One of the classic signs of exertional heat stroke is CNS dysfunction characterized by confusion, irrational behavior, decreased mental acuity and emotional instability. Other possible signs and symptoms of heat-related illness include nausea, vomiting, diarrhea, headache, dizziness, increased heart rate and decrease blood pressure – all are clinical signs of greater cardiovascular stress and a failing thermoregulatory system.
Most, if not all, heat deaths associated with football are caused by exertional heat stroke and are completely preventable. The NCAA, acting upon recommendations from the National Athletic Training Association in conjunction with the American College of Sports Medicine, has adopted guidelines and implemented preventative strategies that have been very successful in limiting the number of heat-related illnesses in collegiate football players. Importantly, the practice schedules have been modified to induce a gradual heat acclimation. Heat acclimation occurs over a number days of successive exposures to exercise and heat, with characteristic physiological changes including a decreased resting body core temperature and an increased sensitivity of the thermoregulatory system by increasing plasma volume.
Despite the success of these simple changes to the practice schedule in reducing the number of heat-related illnesses in collegiate athletes, the governing bodies that regulate high schools athletics have yet to adopt similar guidelines. Education and simple changes to traditional August football practices saves lives.