Jan 29, 2015
When They’re Hot…

Being prepared to treat heat illness is essential, but it’s even better to follow smart prevention steps that keep athletes from needing treatment at all.

By J. Allen Hardin

J. Allen Hardin, LAT, ATC, PT, MS, SCS, CSCS, is Co-Director of Athletic Training/Sports Medicine at the University of Texas. He can be reached at: [email protected].

Here’s a staggering fact that shouldn’t be true, but is: Heat illness is the third leading cause of death among high school athletes in the U.S.

It shouldn’t be true because in the vast majority of cases, heat illness is preventable with little more than common-sense precautions. And when it does occur, early detection and proper management can minimize if not eliminate the mortality risk. In short, there’s no good reason for most of the heat-related deaths that occur on athletic practice fields every year.

Many factors contribute to the body’s ability to regulate internal temperature during exercise. Air temperature, humidity, sun exposure, workout intensity, hydration status, supplement use, and the athlete’s fitness level and acclimatization all play a role. Armed with the latest information and strategies for evaluating and dealing with heat risk in any situation, you can keep your athletes cool, safe, and performing at their best.


“Heat illness” is an umbrella term that encompasses several different conditions of various severity. The four most commonly recognized categories are:

Heat cramps. Exercise-associated muscle cramps are a common result of working out in hot weather, particularly when accompanied by profuse and prolonged sweating. The exact etiology is unknown, but cramping is most likely associated with low serum electrolyte concentration secondary to sodium depletion. It is characterized by acute, painful involuntary skeletal muscle twitching and spasms, usually affecting the arms, legs, and abdomen.

Some athletes are naturally more susceptible to heat cramps than others, and this may be explained by individual differences in sodium balance. When compared to athletes with no history of cramping, research has found that crampers are generally “salty sweaters,” losing as much as twice the sodium through their sweat as non-crampers. In addition, they usually have a higher sweat rate, increasing both salt loss and dehydration.

Heat cramps can obviously be debilitating on their own. But they may also serve as an early indicator of impending heat exhaustion, as well as a warning sign that an athlete is dehydrated.

Heat syncope. This condition presents as an orthostatic syncopal episode (fainting) or lightheadedness during exposure to hot temperatures. It’s most often seen after a bout of extreme effort, when the blood vessels are maximally dilated. Predisposing factors include exercising without a cool-down period and being in a dehydrated state during physical activity.

Like with cramps, some athletes are naturally more prone to heat syncope than others. If an athlete has experienced a syncopal episode before, they are often more likely to experience another in the future due to innate cardiovascular characteristics, so they may warrant additional monitoring during workouts.

Heat exhaustion. By definition, this is a physical inability to continue exercise in the heat, and it is associated with heavy sweating, dehydration, sodium loss, and energy depletion. Also known as exertional hyperthermia, it occurs when an athlete performs strenuous exercise in the heat and loses large amounts of fluid and electrolytes through sweat.

Symptoms include profuse sweating, fatigue, general malaise, nausea, vomiting, the urge to defecate, headache, hyperventilation, an elevated heart rate (tachycardia), hypotension, vertigo, anxiety, and confusion. Dangerous clinical manifestations include circulatory collapse and increased core temperature, ranging from slightly above normal up to 104.9 degrees Fahrenheit (this is generally considered the cut-off for heat stroke).

There are two classifications of heat exhaustion: water-depletion and sodium-depletion. Water-depletion heat exhaustion usually occurs during one particularly grueling exercise session, while sodium-depletion exhaustion usually shows up after several days of exercising in a hot environment. The water variety has a more rapid onset and is more likely to progress to heat stroke if untreated, but the sodium variety is equally serious because it may lead to a “hyperhydrated” status called hyponatremia, in which the body’s sodium level becomes low enough to possibly cause heart attack, seizure, or even death.

Exertional heat stroke. This most extreme form of heat illness is characterized by a core temperature of greater than 104.9 degrees Fahrenheit accompanied by signs of organ system failure. It is life-threatening and should be considered an immediate medical emergency.

The degree of physical damage depends on how high the individual’s core temperature reaches and how long it remains elevated. A heat stroke diagnosis is typically made when a severely elevated rectal temperature and changes in mental status follow physical activity with heat exposure.

The signs of exertional heat stroke include tachycardia, hypotension, sweating (although the skin may also be dry at the time of collapse), hyperventilation, altered mental status, irritability, lack of muscle control (ataxia), vomiting, diarrhea, seizures, coma, and decorticate (abnormal) posturing.


Even light or moderate exercise that’s easy to perform in cool conditions can become extremely difficult during an athlete’s first exposure to hot weather in a long while. However, repeated exposure to a hot environment produces physiological changes that improve work capacity and thermoregulation. This acclimatization process is one of the most critical concepts to understand in order to keep athletes safe in the heat.

Acclimatization occurs through a series of adaptations in the body, including decreased heart rate, decreased internal temperature, and increased plasma volume and sweat rate. Essentially, the body “learns” that its response to exercise shouldn’t be the same on an 85-degree day as on a 65-degree day. Over time, the same amount of work in hot weather becomes less physically stressful, and an athlete can work harder and longer without an increased health risk.

How exactly to structure an acclimatization period varies based on an athlete’s initial conditioning level, body composition, and natural physiology, along with the intensity of work, weather conditions, and other factors. Most acclimatization occurs during the first week of heat exposure, and in the majority of cases, a reasonable degree of acclimatization has set in by day 14. However, in the most extreme cases (such as with very hot, humid weather or a highly deconditioned state), athletes may not be fully acclimatized for two to three months.

While acclimatization may be the most important longer-term guard against heat illness, hydration is a critical short-term consideration. Acclimatized or not, athletes who aren’t properly hydrating before, during, and after workouts–especially in the heat–are at much greater risk for serious health problems than athletes who are.

Dehydration occurs any time an athlete loses more fluid (mainly through sweat and urine) than they replenish through drinking. It can occur acutely within a workout, or cumulatively over the course of multiple days, and the effects can be devastating. Sweat is the body’s primary means of cooling during exercise, and without an adequate volume of fluid to perspire, thermoregulation is severely hampered. In addition, dehydration can cause cramping, decreased cardiovascular performance, mental status changes (such as confusion), and in extreme cases, organ failure and death.

How do you know if an athlete is properly hydrating? One of the best methods is monitoring daily pre-practice and post-practice body weight. Athletes should be drinking enough during activity to replace 16 to 20 fluid ounces per pound lost due to sweat, meaning their pre- and post-practice weight should be roughly the same. A good starting point is to aim for at least eight ounces of fluid intake every 20 minutes during activity, and if the athlete is still found to be losing weight during workouts, this number should be adjusted accordingly.

From a clinical standpoint, a combination of total-body water and plasma osmolality testing provides the “gold standard” for hydration assessment, but because these methods require considerable expense, resources, and analytical expertise, they aren’t practical for day-to-day hydration status monitoring. An easy and reliable alternative is self-monitoring urine color–athletes should be advised to notice how dark their urine appears all day long. A general rule is the clearer the better, and urine with a dark yellow shade (similar to apple juice or darker) indicates that the body is not adequately hydrated. Frequently feeling thirsty is another potential sign of dehydration, but thirst sensation naturally varies from one person to the next, so its absence shouldn’t be interpreted as a sign that an athlete is properly hydrated.

Two important buzzwords in heat illness prevention are prehydration and rehydration. The best available evidence suggests athletes should ingest at least 16 to 20 fluid ounces of water or a sports drink two hours prior to physical activity to promote good hydration status and “kick start” the body’s absorption mechanisms. In particularly hot conditions, they should drink another 10 to 20 fluid ounces 30 to 60 minutes before exercise.

After exercise, post-workout weight should determine how much the athlete must drink to rehydrate. Any time they’ve lost weight due to a workout, they should drink enough fluid to return to pre-activity weight. Sports drinks are a better option than water, as they replenish sodium and other electrolytes lost through sweat, along with carbohydrates and other ingredients that help replace glycogen stores.

The effects of dehydration on overall health and safety can’t be overstated. During exercise in hot weather, research shows that fluid loss of just two percent of body weight may predispose an athlete to exertional heat illness. Furthermore, core body temperature has been shown to rise by roughly .25 to .35 degrees Fahrenheit for every one percent of body weight lost to dehydration during exercise.

Not surprisingly, one more key physical factor in heat stress risk is conditioning level. Those who are out of shape–with a higher body fat percentage, or who have been sedentary in their off-season, for instance–are less able to internally regulate body temperature. They also typically lose more sodium through sweat than athletes who are better conditioned. These athletes, commonly football offensive and defensive linemen, require closer observation during workouts in hot weather, especially during the acclimatization period.

As part of standard pre-participation physicals, every athlete should be asked about any history of heat illness symptoms–even ones they may consider minor, such as occasional lightheadedness or cramping during workouts in the heat. Athletes who have a history of heat illness also warrant special attention and close monitoring during workouts.


Even if you make sure athletes follow an acclimatization schedule, are well hydrated before, during, and after workouts, and don’t push themselves beyond safe activities for their conditioning level, it’s still possible they’ll be struck by some degree of heat illness. While prevention steps are essential, it’s equally important to have a plan in place for fast and effective detection and treatment of all forms of heat illness.

Cramps are the easiest to treat, typically through temporary removal from activity for oral rehydration and sodium replacement through sports drinks and/or salt tablets. In cases of severe cramping, intravenous fluid replacement may be necessary. Because of the clear link between cramping and heavy sweating (that is, dehydration and salt loss), athletes who struggle with cramps should be encouraged to consume fluid and sodium more frequently during exercise.

Heat syncope can also be treated simply in most cases. The athlete should be placed in a supine position, preferably in a cool indoor facility or at least out of the sun, and provided with fluids orally or intravenously. An athlete’s core temperature should be monitored after syncope or lightheadedness to ensure that a more serious form of heat illness is not present.

In cases of heat exhaustion, intervention should consist of immediate removal from activity for cooling and rehydration as soon as symptoms occur. In mild cases, in which the athlete has normal vital signs and is not vomiting, this alone is usually adequate. In athletes with altered mental status, cardiac arrhythmia, or vomiting, or when the more conservative measures fail to improve their condition, treatment with intravenous rehydration, more intensive cooling (such as an ice bath), and careful monitoring may be required, as untreated heat exhaustion can lead to heat stroke.

If you follow the prevention and early intervention strategies outlined so far, heat stroke will hopefully never affect one of your athletes. If it does, however, treatment begins with monitoring respiratory and cardiac status and managing any findings according to first-aid protocols. Rapid external cooling to bring down the core temperature is critical for minimizing harm, and the generally accepted best method is cold water or ice water immersion.

In addition, every program should have an emergency action plan in place. It’s important to cover all the details, such as arrangements for summoning an ambulance and providing it with easy access to the field, immediate availability of cold submersion, and having a method to monitor vital signs and core temperature until the athlete can be transported to the hospital.


Hopefully, most of what you’ve read so far has reinforced what you already knew. Heat illness has received much attention in the sports medicine community in recent years, so today’s athletic trainers are more educated on the topic than ever before. But there are a few points of advice on minimizing risk that I believe every program can benefit from.

Watch the weather. Environmental factors that affect exertional heat illness risk include ambient air temperature, relative humidity, air motion, and the amount of radiant heat from the sun. The best way to judge the risk on any given day is wet bulb globe temperature (WBGT), which accounts for all these factors. Every athletic department with athletes who work out in warm weather should have a way of gauging the WBGT, the easiest being a wet bulb globe thermometer.

Recommendations for the threshold above which athletes shouldn’t exercise outdoors vary from one researcher to the next. In general, if the WBGT is above 82 degrees Fahrenheit, an athletic event should be delayed, rescheduled, or moved into a controlled climate. In the mid to high 70s and around 80, outdoor activity should at least be modified to reduce physical stress.

Interestingly, because of the cumulative nature of dehydration and heat’s impact on the body, the day after a high-WBGT day carries additional risk as well. In fact, some experts have found that the previous day’s WBGT may be one of the best predictors for incidence of exertional heat illness.

Talk about supplements. For better or worse, athletes often seek to boost their performance, energy level, or muscle growth with over-the-counter dietary and nutritional supplements. Many of these products are harmless if used properly, but some carry significant health risks, particularly for athletes exercising in the heat.

Stimulants, for example, speed the rate of increase in core temperature and augment the body’s heat production. These products, which range from amphetamines to herbal ephedra and caffeine, put athletes at greater risk for exertional heat illness, and some can contribute to dehydration as well. They may also trigger serious side effects, including dizziness, headache, gastrointestinal distress, heart palpitations, heart attack, stroke, and seizure.

Even supplements generally considered benign, such as vitamins, minerals, creatine, and protein powders, can be harmful if taken beyond the recommended doses. And because supplement makers remain largely unregulated, some products are contaminated during the manufacturing process. According to a few estimates, up to 25 percent of dietary supplements may contain substances not listed on the label.

The best defense against supplement problems is education. Talk to your teams and individual athletes about any products they may be taking, and discuss how they can usually achieve their goals by improving nutritional habits without the need for supplementation. For those who want to continue using a product, at least ensure that they are following dosage instructions to minimize the risk of negative side effects.

Change clothes. Clothing creates a barrier to evaporation, impairing the body’s ability to dissipate heat. The material properties and how much skin is covered determine the impact on thermoregulation and heat tolerance.

Athletes who wear apparel and equipment that doesn’t allow for heat dissipation are obviously at increased risk for exertional heat illness. Before a workout, think about how much clothing and padding will be required, and advise athletes to remove any unnecessary barriers to heat release. On hot days, you might consult with a team’s coaching staff to modify a workout so that less padding is necessary. And it’s always smart for athletes to wear light colored clothing that reflects light and minimizes heat absorption.

Encourage vigilance. Even the most diligent athletic trainer can’t be watching all athletes at all times. Athletes themselves can help you by serving as extra eyes and ears to detect any signs of exertional heat illness among their teammates.

Every athlete should know the symptoms of heat illness and be instructed to report to an athletic trainer when they see someone who may be struggling. Some of the more subtle signs, such as confusion or altered mental state, will most likely be noticed by teammates before anyone else. In addition, all parents and coaches should be educated on heat illness symptoms, so that problems can be identified as soon as possible in any workout setting.

As long as athletes and hot weather coexist, the dangers of heat illness cannot be ignored. The body’s ability to regulate cardiovascular homeostasis, internal temperature, and muscle function can be compromised due to the potentially deadly combination of heat, dehydration, and physical stress. But with a proactive approach rooted in prevention, education, and preparedness, you can rest assured that your athletes are as safe as possible.

REFERENCES To view full references for this article, go to: www.Training-Conditioning.com/References.



The NATA’s position statement and tips for recognizing, preventing, and treating heat illness can be found by searching “heat illness” at: www.nata.org.


The American College of Sports Medicine’s consensus statements and other documents on heat illness and hydration can be found by searching “heat illness” at: www.acsm.org.


The Centers for Disease Control and Prevention has an entire Web site devoted to extreme heat and its effects. A prevention guide, the signs and symptoms of heat illness, extreme weather tips, and other resources can be found at: www.bt.cdc.gov/disasters/extreme-heat.


To view the NCAA’s Out-of-Season Football Conditioning Educational Initiatives, search for “Football Conditioning” at: www.ncaa.org.


Heat illness prevention information aimed at the high school sports community can be found by searching “heat illness” at the Web site of the National Federation of State High School Associations: www.nfhs.org.

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