There’s something extra motivating about taking your workout outside in the summer. Maybe it’s a scenic early morning run as the sun rises, a long bike ride on a weekend morning, or a bootcamp class at your local park. Or maybe you’re driven to mix up your workouts for the sake of longevity, taking them outside, rather than to the gym.
As refreshing as outdoor exercise can be, soaring temperatures and sticky humidity can quickly take routine workouts into the danger zone. Heat-related illnesses send over 67,000 people to emergency rooms every year, and athletes aren’t immune. In fact, some of the most serious cases happen when exercisers push through warning signs, shrugging them off as discomfort, says Shane Cole, M.D., an emergency medicine physician and founder of iCare ER and CAM Innovative Services.
It’s easy to underestimate how quickly heat stress can build. “Humidity is the hidden danger,” Cole says. “At 90% humidity, your sweat cannot evaporate, which is your body’s main cooling system, so a 90-degree day can stress you like a 105-degree day.”
The good news? A few smart adjustments can help you avoid heat exhaustion during summer workouts, continuing to exercise outdoors safely all season long. Here’s what sports nutrition and medical experts want you to know.
- ABOUT OUR EXPERTS: Shane Cole, M.D., is an emergency medicine physician and the founder of iCare ER and CAM Innovative Services. Cassandra Padula Burke, M.F.S., R.D.N., L.D., C.P.T., is a medical fitness specialist, registered dietitian and certified personal trainer. She coaches triathletes and endurance athletes and owns Catalyst Nutrition & Performance in Maryland.
What Are the Signs of Heat Exhaustion?
Feeling sweaty, flushed, and tired after spending time outdoors on a hot day is normal. But when your body starts struggling to cool itself effectively, heat exhaustion can set in. As you sweat, you lose fluids and electrolytes, and your cardiovascular system is essentially working overtime. “When you lose too much fluid and salt through sweat, and your cardiovascular system cannot keep up with the demand to cool the skin and fuel the muscles, the system starts to fail,” explains Cole.
During heat exhaustion, your blood pressure drops, leaving you feeling weak, dizzy, and nauseated. Your temperature can be in the range of 101-104 degrees Fahrenheit, according to the Cleveland Clinic. Other common symptoms of heat exhaustion include:
- Lightheadedness
- Cool moist skin with goose bumps
- Headache
- Excessive sweating
- Muscle cramps
- Weakness or unusual fatigue
- Rapid heart rate
- Fast, deep breathing
During heat exhaustion, you may feel miserable, but you’re typically still alert and mentally clear.
Heat stroke, however, is a medical emergency. It occurs when the body’s cooling mechanisms fail completely, causing the core temperature to rise above roughly 104 degrees Fahrenheit. This can trigger changes in mental status, such as confusion, agitation, slurred speech, seizures, or loss of consciousness. “The mental status change is the red flag I want every coach, parent, and gym buddy to know,” says Cole. “Confusion plus a hot, exhausted athlete means call 911 and start cooling now.”
Who’s at Risk of Heat Exhaustion?
Some people face a higher risk of heat-related illness than others, Cole explains. Those most vulnerable include people who aren’t acclimated to hot weather, older athletes, people with larger body sizes, and anyone taking medications that affect hydration or the body’s ability to regulate temperature. (These include diuretics, certain blood pressure medications, stimulants, and some antihistamines.) Athletes who wear heavy protective equipment, such as football players in full pads, are also at elevated risk, as are those who have experienced heat illness in the past.
Read More: Triathlon Training Tips: How to Nail Your First (or Fastest) Race
Tips to Avoid Heat Exhaustion During Summer Workouts
Heat exhaustion can do more than make you feel lousy. It can sideline your workout, cut your training short, and, if shrugged off, increase the risk of a more serious heat-related illness.
As temperatures climb, these expert-backed tips can help you avoid heat exhaustion during outdoor workouts.
1. Give Your Body Time to Acclimate
If your spring workouts happened mostly indoors, resist the urge to jump straight into outdoor workouts at the start of summer. Going from an air-conditioned spring workout schedule straight into an all-out summer workout is one the most common mistakes Cole says he sees among athletes who end up with heat-related illness.
Another common culprit? Traveling from a cool climate to a hot one and not easing into workouts slowly. It actually takes 10-14 days of consistently training in outdoor summer heat for your body to acclimate, explains Cassandra Padula Burke, M.F.S., R.D.N., L.D., C.P.T., registered dietitian, certified triathlon and endurance coach, and owner of Catalyst Nutrition & Performance in Maryland.
During that adjustment period, start with shorter, easier workouts and gradually increase duration and intensity over a two-week period, she recommends. Your body becomes more efficient at sweating, regulating temperature, and maintaining cardiovascular performance as it adapts to the heat.
2. Stay Hydrated
One of the biggest mistakes outdoor athletes make is waiting until they feel thirsty to drink. You’ve probably heard it before, but by the time you feel thirsty, you are already behind, Cole says.
“When you exercise, your muscles generate a lot of heat,” Cole explains. “Your body sheds it two main ways: It sends blood to the skin to radiate heat out, and it sweats so that evaporation pulls heat off the skin.” So, if you’re dehydrated, he explains, it becomes harder for your body to cool itself efficiently through sweating, increasing the risk of heat exhaustion.
Hydrate in the 1-2 hours ahead of training, aiming for pale yellow urine going into a training session, Burke says. “Planning beats reacting to the situation every time,” Burke says. “The single most effective strategy is beginning training sessions hydrated and already fueled, because once your hydration falls behind it is too late.”
3. Don’t Overlook Electrolytes
For workouts lasting an hour or less in mild conditions, plain water is usually enough for hydration, Burke says. But when temperatures climb and you’re sweating heavily, electrolytes become much more important.
That’s because sweat doesn’t just carry away water. It also depletes electrolytes—aka the minerals that help regulate fluid balance, support muscle contractions, and keep nerves firing properly. Of those electrolytes, sodium deserves the most attention during hot-weather workouts because it’s lost in the highest concentration through sweat, Burke says. While potassium, magnesium, and calcium are also lost, they’re generally easier to replace through a balanced diet.
Electrolytes become increasingly important during workouts lasting longer than 60-90 minutes, in hot or humid conditions, or for people who are “salty sweaters.” One telltale sign you’re a salty sweater: white salt residue on your skin, face, or workout clothes after exercise. “The first question I ask athletes is how they sweat,” Burke says. “If they finish training sessions with gritty residue (salt crystals) on their face and skin or white residue on their clothing, they are a salty sweater and need more sodium than most sports drinks deliver.”
When choosing an electrolyte product, Burke recommends looking for one that contains sodium, potassium, magnesium, and calcium, with sodium taking priority. Average sweaters often do well with about 400-700 milligrams of sodium per serving, while heavier or saltier sweaters may need closer to 1,000 milligrams. For athletes who lose a lot of sodium through sweat, Burke recommends LMNT, which delivers 1,000 milligrams of sodium per packet. Be sure to pair this with adequate fluid replacement, generally about 16-24 ounces per hour, Burke says.
Read More: Which Electrolyte Supplement is Right For You?
4. Exercise During the Coolest Parts of the Day
If you’re taking your workouts outdoors—and don’t want to overdo it—timing can be everything. Burke recommends scheduling outdoor workouts for early morning or after sunset whenever possible. “My general rule is to do hard workouts in the early morning or after sunset and wear lightweight, sweat-wicking fabrics,” she says. Midday workouts, on the other hand, expose you to stronger sunlight, higher temperatures, and often peak heat-index conditions.
Another pro tip: Don’t focus solely on the temperature forecast. “People look at the temperature and feel fine about it, not realizing the humidity has shut down their cooling system,” says Cole. Before heading outside, check the heat index, which combines temperature and humidity to reflect how hot it actually feels. If the heat index is especially high, consider shortening your workout, reducing intensity, or moving it indoors.
5. Take Cooling Breaks Before You Feel Like You Need Them
Cole recommends building short cooling breaks into longer outdoor sessions, even if you’re feeling good. Heat exhaustion can sneak up on you as body temperature slowly increases. “Even a 60-to-90 second pause in the shade every 15 minutes lets your core temperature settle,” he says. These breaks can be a great time to hydrate, too!
The Bottom Line
To avoid heat exhaustion during summer workouts, you don’t have to retreat to the treadmill in an air-conditioned gym all summer. Enjoy the scenery and the fresh air. Staying hydrated, acclimating gradually, paying attention to the heat index, replacing electrolytes when needed, and listening to your body’s warning signs can help you safely enjoy outdoor exercise all season long.