The dangers of exercising in heat

August is typically the hottest month of the year in the Midwest.   But with the current trend in "hot" exercises ranging from "Hot Yoga Bootcamp," to "Hot Spinning" to "Hot Hula Hooping,"  every month is the hottest.  So whether you train outside in the summer heat or inside in a heated room it is very important to be aware of how heat and humidity can impact your body and your physical performance.  More importantly you need to know how to prevent potentially deadly heat injuries in yourself and your fellow exercisers.

In recent years, several professional and college athletes have died from heat stroke.  In fact between 1995 and 2007, there were 31 deaths in the United States due to heat injury in high school football alone.  A total of 21 college football players have collapsed and died during conditioning workouts since 2000.  According to NOAA there was 206 heat related fatalities in 2011.  If you don't think that heat has an impact on performance then consider what happened at the Chicago Marathon in 2007.   It was October 7, 2007 and what should have been a perfect day for the 30th annual race.   But with 88 degree temperatures and humidity to match, organizers were forced to shut the race down in the middle and more than 300 runners required medical attention and one died.  Surprised?   Marathon runners are among the most physically conditioned athletes;  however, high temperatures and humidity were no match for their training.

It is clear that people are obsessed with sweat. A recent New York Times article takes a look at the hot trend and asks the burning question: what gives, heat misers?  According to the article, fitness fanatics with disposable income are spending top dollar to sweat their brains out in classes that make Bikram‘s 105 degree heat feel like a stroll through a cool spring breeze.  A small but growing upscale clientele, most conditioned to years of regular workouts, won’t leave the locker room for much below 90 degrees. (Typical gyms are 68 to 72 degrees, in line with American College of Sports Medicine guidelines) We’ve seen the rise of hot yoga in recent years, and we get that there are some benefits to heated rooms: more pliable muscles, the feeling of a good sweat and the challenge of doing the same work, but being really hot while doing it.  But the hot exercising trend is getting extreme and is likely to cause more harm than good. Most of the trend tends to be driven by a confusion of the role of heat in physiological performance and health and that may include confusion as to safety precautions and treatment of heat injuries.  For example Alexandra Cohen, 42, the supervising producer of “The View" says, “I don’t have time for hours in the gym doing cardio and weights and then sitting in the steam room to detox.”  “A good day is when I have to literally wring my clothes out,” she said. “Some people do crazy cleanses. I do hot-room workouts.” She mused: “I tell you, your body adjusts. I probably need to make it harder at this point.”  So if you have the desire to feel like you’re vinyasa-ing through the Sahara Desert or cross-fitting in the soupy thick humidity of the equatorial jungle tropics then learn about how your body responds to heat.  More importantly follow the following advice on how to prevent and treat heat injuries.

There are many types of heat injury, ranging from mild heat cramps to life-threatening heat stroke.  "Heat can kill you," says William O. Roberts, M.D., medical director for the Medtronic Twin Cities Marathon in St. Paul, Minnesota. "That's why we have to be so careful with it, especially runners."

Exercising in sauna like conditions can throw your internal equilibrium seriously out of whack. As the temperature outside begins to rise, the difference between normal skin temperature (90º F) and the ambient temperature narrows. As the ambient temperature rises above 80º F the difference between the normal skin temperature and the ambient temperature is not great enough to allow the body's internal heat to flow away from the body by convection. Instead, the body reacts by cooling itself through a process known as evaporative cooling.  The body normally cools itself by moving blood—which is mostly water—to sweat glands in the skin, says Douglas Casa, Ph.D., A.T.C., COO of the University of Connecticut's Korey Stringer Institute. The glands create sweat droplets that carry heat to the surface of the skin, where it evaporates.

"The droplets of sweat are like little containers for the heat," Casa says. When you continue to run, your organs and working muscles compete for a limited blood supply, which compromises this cooling system. Humidity compounds the problem, by hindering the evaporation of sweat, making it harder to cool yourself. And runners performing intense exercise in hot weather tend to become dehydrated, says Casa. "With less water in the body, you have less blood plasma volume—the liquid portion of your blood—to serve all your needs."  The heat index measures danger of heat, humidity and can be a good guide for avoiding certain times of day or changing clothing when exercising outdoors.  Dr. Casa said that while there’s no question that hot workouts are harder, any benefits peak at about 100 degrees. “Above that, you’re just jeopardizing safety."

The trainer Tracy Anderson, whose clients have included Gwyneth Paltrow and, at one point, Madonna, said her research put the sweet spot for safety but “a muscle state that promotes change” at 86 degrees and 65 percent humidity. Dr. Casa judged that that was about right, “at least for sweat effect.”  OK, but all that sopping sweat is totally detoxing your body right?   Not exactly.  “That’s a hoax,” [Casa] said. “I don’t think there’s any inherent advantage to sweating more.  Some people just like the feeling.”  “Less than 1% of toxic metals are lost through sweat” says Dr. Donald Smith, Professor of Environmental toxicology at UC Santa Cruz.  Excessive sweating can actually be very detrimental to your body's natural detoxification system-the kidneys.   In order to produce sweat you need water and that is taken from the blood stream.  Excessive sweating stresses the kidneys out because there is less volume of water in your blood and thus the blood is thicker, and thus harder to filter through the kidneys.

Does exercising in heat burn more calories?  It gives you the feeling that you're burning tons of calories, but your body isn't increasing physical output to increase its temperature, that is being imposed from the outside.  Really you're just losing a lot of water.   When you sweat you will temporarily lose weight—but this weight is just water weight (water and electrolytes) and not fat weight, and you will put it straight back on as your body is re-hydrated. In addition, as little as a 2% loss of body mass from fluid loss will impair exercise performance. This means a 150-pound student who loses roughly 3 pounds during a heated yoga class from excessive sweating can experience increased heart rate and decreased blood volume, causing a loss of strength and endurance.  There are four typical heat injuries that result from exercising in hot, humid conditions:  Heat cramps, heat syncope, heat exhaustion and heat stroke.

Heat cramps are painful cramps in the stomach, arm, and leg muscles. These cramps are caused by not replacing salt and fluids during intense, prolonged exercise in the heat.

Treatment for Heat Cramps

• Stop exercise activity
• Gently stretch affected muscles
• Drink cool water or an electrolyte solution (low in sugar)
• For severe symptoms, treat as heat exhaustion (see below)

Weakness, fatigue, and fainting are the chief symptoms of heat syncope. They are typically brought on by exercising hard in the heat. Too much salt and water are lost through perspiration, and are not replaced.  Heat syncope often occurs during the first 5 days of adjusting to a new activity. It also can occur in people taking diuretic medicines or those with pre-existing heat illness. Young athletes returning to play after time off for injury are also at greater risk for heat syncope.  Without treatment, heat syncope can put you at risk for heat stroke.

Heat exhaustion is brought on by heavy sweating and results in extreme weight loss. As heat exhaustion sets in, perspiration decreases, and skin and body temperatures rise. Core body temperature typically rises to 104 degrees F.  Additional signs of heat exhaustion include excessive thirst, weakness, headache, and sometimes unconsciousness.   Common signs of heat exhaustion due to salt depletion are nausea and vomiting, frequent muscle cramps, and dizziness.  You are at risk for this type of heat exhaustion when you do not sufficiently replace normal body salts and minerals. This can sometimes happen during prolonged exercise if water alone is used to replenish fluids.

Treatment for Heat Syncope and Heat Exhaustion

• Move the person to a cool, shaded area
• Remove tight clothing
• Give fluids, if the athlete is conscious
• Apply active cooling measures, such as a fan or ice towels, if the core temperature is elevated
• Refer to a physician to assess the needs of fluid/electrolyte replacement and further medical attention, especially if nausea and vomiting are present

Heat stroke is the most severe form of heat injury. When suffering from heat stroke, your body cannot cool itself. This is an acute medical emergency. Quickly recognizing symptoms and responding is critical. Heatstroke is characterized by a core body temperature greater than 104 degrees, increased heart rate, abnormally low blood pressure, sweating, hyperventilation, disorientation and confusion, dizziness, irrational behavior, irritability, headache, inability to walk, loss of balance or muscle function, vomiting, diarrhea, collapse, seizure and coma.  Heat exhaustion can have some of the same signs, but a major difference is that the body temperature (obtained rectally) is below 104 degrees.  Heat stroke is medically defined as core body temperature greater than 104 degrees F.  The skin is typically hot, dry and pink.  Heat stroke may occur with no preceding signs of heat injury. It can also occur as a progression from heat syncope and heat exhaustion.  Again, this is a medical emergency.

Treatment for Heat Stroke

• Move the person to a cool, shaded area
• Remove all equipment and excess clothing.
• Cool the athlete as quickly as possible within 30 minutes via whole body ice water immersion (place them in a tub/stock tank with ice and water approximately 35–58°F); stir water and add ice throughout cooling process.
• If immersion is not possible (no tub or no water supply), take athlete into a cold shower or move to shaded, cool area and use rotating cold, wet towels to cover as much of the body surface as possible.
• Maintain airway, breathing and circulation.
• After cooling has been initiated, activate emergency medical system by calling 911.
• Monitor vital signs such as rectal temperature, heart rate, respiratory rate, blood pressure, monitor CNS status.
• If rectal temperature is not available, DO NOT USE AN ALTERNATE METHOD (oral, tympanic, axillary, forehead sticker, etc.). These devices are not accurate and should never be used to assess an athlete exercising in the heat.

Exercising in the heat does not have to be dangerous if we follow certain precautions.  The number one is to check our ego at the door of the studio or our house.  Pay attention to signs and indicators of heat injury.  Most importantly, if an activity seems to be over the top in terms of the environment or your physical ability, it probably is.

General Guidelines

• See a doctor before starting a new exercise activity. Discuss recent illnesses or medications that could cause dehydration. Cardiac or pulmonary conditions can also contribute to heat injury.
• Take time to adapt to a new activity or climate. Coaches should plan pre-season conditioning programs. These should be held during weather conditions similar to a typical practice.
• Increase the intensity and duration of your exercise program gradually. If you participate in sports that require protective equipment, avoid wearing it at the start of training.

Recommendations

• Allow frequent periods of rest and hydration during activity. Fluid replacement is essential to preventing heat injury.
• Make sure you are well hydrated before, during, and after exercise. Replace your fluids, whether you feel thirsty or not.
• A general recommendation is to drink 24 ounces of non-caffeinated fluid 2 hours before exercise.  The ACSM guidelines suggest drinking anywhere from about 14 to 27 ounces per hour, with the higher end of the range applying to "faster, heavier individuals competing in warm environments and the lower rates for the slower, lighter persons competing in cooler environments.
• Monitor the color of your urine. The darker your urine, the less hydrated you are and the greater your risk for heat injury. Drink enough fluids to keep your urine a very light color.
• Weigh yourself before and after activity to monitor water loss. Make sure you have replaced fluids before your next exercise session.
• Gradually increase activity in the heat over a period of 7 to10 days to allow adequate acclimatization.
• Wear light-weight and light-colored clothing.
• Protect against sun exposure with sunscreen.
• Schedule outdoor exercise at the coolest time of day, either early morning or after sunset.
• Routinely monitor changing weather conditions. Pay close attention to temperature and humidity (indoor/outdoor).
• Strongly consider postponing or cancelling your activity when there are extreme heat and humidity conditions.