How to Adapt Your Workouts to Hotter Weather This Summer
Exercising in high temperatures can be dangerous, but adapting to the heat can have benefits if done carefully
Experts say that when you are exercising and temperatures climb into the 90s, take breaks, drink plenty of fluids and be prepared to slow down or quit.
By Betsy Morris, WSJ
July 3, 2022 6:00 am ET
High temperatures and heat waves this summer mean you need to take extra care in exercising outside.
Heat caused Phoenix to close some hiking trails in June and organizers of Canada’s recent Manitoba Marathon to stop the race partway through. Working out when it’s hot can be dangerous. Heat illnesses, like heat cramps and heat exhaustion, can develop quickly and with little warning. Heat stroke, a condition in which the body overheats and can’t cool itself down, can be deadly.
Yet adapting to the heat can be beneficial if it’s done carefully, gradually and with common sense, researchers who study exercise and physiology have found. Heat acclimation can improve an athlete’s performance in both hot and cool weather, says Christopher Minson, a cardiovascular physiologist at the University of Oregon who works with college, Olympic and professional athletes.
Here’s what he and other scientists advise for exercising in peak summer.
If temperatures rise suddenly, don’t attempt your usual workout at the same intensity, physiologists and trainers say. Start with shorter bouts of easier exercise, Dr. Minson says. Schedule workouts during the early morning or early evening; avoid the hottest part of the day, generally 11 a.m. or noon to 4 p.m. or 5 p.m., depending on where you live. When temperatures reach into the 90s, be careful to take breaks, drink plenty of fluids and be prepared to slow down or quit.
Our bodies get more efficient as they adapt to heat, scientists say. Core temperature and heart rate decrease. We are better able to retain essential minerals like sodium and chloride, calcium and potassium that we lose through sweat. The changes have the effect of lowering the intensity of the exercise and the stress on our systems, says Robert Huggins, president of research and athlete performance and safety at the Korey Stringer Institute, which is focused on heat-illness prevention.
Trying to train your body to work out in the heat isn’t recommended unless you’re already at a strong level of fitness, he says. Adults should first be doing at least 2½ hours of moderate-intensity exercise or an hour and 15 minutes of vigorous aerobic exercise a week, preferably spread throughout the week, he says.
Understand the weather
Take time to figure out the weather conditions most relevant to the exercise you’re planning to do; knowing the air temperature often isn’t enough. The temperature measurements that are most helpful for outdoor exercisers combine air temperature with additional weather conditions. These include the “heat index,” which combines heat and humidity, or “real feel” temperatures, calculated to give an idea of how it feels to be outside.
Humidity is an important element affecting the body’s ability to cool off and regulate temperature, says Gabrielle Giersch, a research physiologist at the U.S. Army Research Institute of Environmental Medicine. Sweat is the main way the body cools itself, physiologists say. The higher the humidity, the slower sweat is able to evaporate from the skin, making it tougher for the body to cool itself during exercise, she says.
The metric used most often to gauge outdoor safety by the military, government agencies and sports teams is the Wet Bulb Globe Temperature, measured with a thermometer, the bulb of which is wrapped in a wet wick to capture not just air temperature but humidity and air flow. The National Weather Service defines the WBGT as a measure of heat stress in direct sunlight based on temperature, humidity, wind speed, sun angle and solar radiation.
WBGT can differ widely from temperature. WBGT can be 80 degrees at the same time the temperature outside is anywhere from 71 degrees to 105 degrees, Dr. Huggins says.
The WBGT is commonly used to determine the point at which it becomes too hot to exercise altogether. The limit used by many sports associations and government agencies for such extreme conditions is a WBGT of 86 degrees to 92 degrees depending on where you live. The WBGT for “high-risk conditions” is 84 degrees to 92 degrees. In high-risk conditions, exercise should not exceed one hour that includes four separate four-minute breaks, according to a guide for soccer coaches developed by U.S. Soccer.
The Occupational Safety and Health Administration has a calculator that computes WBGT when you plug in your location (longitude and latitude), wind speed, barometric pressure and other data available on a smartphone.
Air temperature is only one metric to know when setting off to exercise: The higher the humidity, the slower sweat is able to evaporate from the skin, making it tougher for the body to cool itself during exercise.
Spot trouble signs
Exercise with other people and near somewhere you can cool off if you get too hot. Dr. Minson says he sometimes knocks on the door of a house during a run to ask if he could duck into the sprinkler. Wear clothes made of synthetic fabric designed to help move sweat away from the body.
Serious heat illness can occur suddenly and without predictable warning.
Heat illness doesn’t follow a linear progression from involuntary muscle spasms called heat cramps to more serious heat exhaustion, the symptoms of which include heavy sweating and faint rapid pulse, to most serious, which is heat stroke. The symptoms of the different conditions often overlap and don’t occur in a particular order, trainers and physiologists say.
Perception—how hot you feel—can be a useful indicator of heat stress. Dr. Minson uses a one to 10 scale to gauge how well his college students and Olympic athletes are adapting to the heat. A rating of nine or 10, which means miserably hot, is a warning sign, he says.
Other warning signs include dizziness, lightheadedness and fatigue. If those develop, slow down or quit your workout and cool off. If your clothes are saturated, take them off so your sweat can evaporate. Drink fluids; use cold water or towels to cool the body; get into the shade.
If a person becomes disoriented or confused, or stutters or vomits, that can signal heat stroke, the most serious heat illness. In that case, call 911 and get immediate medical help.
“I encourage people to embrace the heat,” says Dr. Minson. “But do it smartly.”