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Is Exercising in the Heat Safe?

Is Exercising in the Heat Safe?

Reading Time: 5 minutes


DATE: 2024-07-01

Summer is a time for fun and to be outdoors, but is it ever too hot out to be active outside? Exercising in the heat can be risky, but you still want to go for a run or play soccer with your friends at the park. 

How much heat you can tolerate depends on individual factors, but everyone has a limit. Learn how to identify your limit, signs that it’s time to cool down, and what to do if you or someone else really gets sick in the heat. 

When Is it Too Hot to Exercise? 

There is no single answer to this question because it depends on the person. Exercise stresses the body, and heat puts additional stress on it. The fitter you are, the more heat you can safely tolerate while working out. For most people, it’s important to be cautious when the heat index is 90 degrees or higher. 

The body operates optimally in a narrow temperature range. When the temperature rises due to heat or exercise (or both), cooling processes in the body kick in to bring it back down. This includes sweating. When sweat evaporates from skin, it carries heat away with it. Your body will also bring blood closer to the extremities to dump more heat.

High external temperatures, high humidity, and heat generated by exercise can all overwhelm the body’s inherent cooling system. This is when exercising in heat becomes unsafe. These are some of the individual factors that make it more difficult to exercise safely in hot weather: 

  • Poor fitness

  • Lack of conditioning or acclimatization to high-temperature exercise

  • Illness 

  • Chronic conditions, especially those that reduce the ability to sweat

  • Dehydration

  • Obesity

  • Alcohol consumption before exercise

  • Certain medications, including antihistamines and stimulants

Humidity is another factor that makes exercise riskier. Moisture in the air interferes with the ability to lose heat through sweat evaporation. 

Are There Any Benefits of Exercising in the Heat? 

Working out in the heat can be risky but may also have some potential benefits if done safely. Training in heat increases your VO2 max more efficiently than other conditions, including training at elevation. It can also increase blood plasma volume. Hot weather training can help you acclimatize to tough conditions.  

While there may be some benefits of exercising in the heat, it is also risky. If you are planning to do heat training, monitor yourself very carefully and know the risks and signs that your body has had enough. 

Check out these fun outdoor activities to stay fit this summer. 

What Are the Risks of Exercising in Hot Weather?

Dehydration is a very common risk of exercising in the heat. Also dangerous are heat injuries or heat illnesses. These occur when the body’s effort to cool itself cannot keep up with its rising temperature. Know the signs of dehydration and heat illness, so you can back off and cool down if necessary. 


When you work out in the heat, you sweat even more than normal as the body tries to cool itself. You can easily get dehydrated if you do not adequately replace sweat with water and electrolytes. 

Signs of mild or moderate dehydration include thirst, muscle cramps, a headache, a dry or sticky mouth, not urinating enough, and cool, dry skin. Signs of severe dehydration also include: 

  • Dry, shriveled skin

  • Irritability

  • Confusion

  • Dizziness

  • Rapid heartbeat and breathing

  • Fatigue

  • Listlessness

  • Loss of consciousness 

Heat Cramps

Like dehydration, heat illnesses start out mild and get progressively worse if not addressed. Heat cramps occur first, with symptoms similar to those of dehydration: thirst, fatigue, excessive sweating, and muscle cramps. The cramps are often in the abdomen and legs. 

Heat Exhaustion

Heat exhaustion is more severe than heat cramps. Symptoms include: 

  • Headache

  • Dizziness

  • Weakness and fatigue

  • Shortness of breath

  • Cool and moist skin

  • Infrequent urination and dark urine

  • Nausea

  • Vomiting

Heat Stroke

Heat stroke is very serious and requires emergency medical treatment. It occurs when the body’s ability to cool itself fails. This causes body temperature to rise quickly and dangerously. Signs include: 

  • A fever of 103 degrees or higher

  • Hot, dry, and red skin

  • Rapid, shallow breathing

  • A fast but weak pulse

  • Extreme confusion

  • Seizures

  • Loss of consciousness

Tips for Safely Exercising in the Heat

Hot weather doesn’t necessarily have to mean skipping a workout. However, you should be cautious. Take these steps for safer, more productive summer workouts. 

1. Hydrate Before, During, and After

It is extremely easy to get dehydrated when exercising in heat, and it can sneak up on you. If you’re working out for an hour or less, water is adequate. For longer exercise, use a sports drink to replenish lost electrolytes. Don’t overdo it, though. Too much water can also be dangerous. Aim for a half to a full liter of fluids per hour of exercise. 

2. Dress Appropriately and Protect Your Skin

Your skin is the primary tool your body has for cooling itself, so protect it. Use sunscreen and wear light, loose clothing that blocks sunlight. Choose breathable, sweat-wicking materials. They promote sweat evaporation to keep you cool. Also consider wearing a hat. 

This post explains the differences between cotton and synthetic materials and why they matter when choosing workout gear. 

3. Workout in the Morning or Evening

Avoid the hottest part of the day, which is also when the sun is most intense. Check weather reports the day before and consider getting up early to fit in a workout during cooler temperatures. An evening workout is also a great option. 

4. Lower Your Workout Expectations and Listen to Your Body

It’s much harder on the body to exercise in heat, so take that into account when planning a workout. If you normally run an eight-minute mile, expect to do nine minutes or slower in heat. This doesn’t mean you’re working any less hard or making less progress. Back off on your effort and even shorten workouts when it’s hot. 

This is one of the most important and often difficult tips to follow for exercising in heat. Fitness enthusiasts and athletes often find it difficult to not finish a workout or not meet a target during exercise. Listen to what your body is telling you, and slow down or stop if necessary. 

5. Know First Aid for Heat Injuries

Even with smart precautions, heat stress injuries happen. Be prepared to apply first aid, either for yourself or someone else. If you notice signs of heat injury, take these steps: 

  • Stop exercising

  • Get somewhere cooler, indoors or at least in the shade

  • Lay down and elevate your legs a little bit

  • Sip water or ice cubes if you have them

  • Douse yourself with water if you can

  • Apply cold cloths to the neck, armpits, and groin

If these steps don’t help, or if you see signs of heat stroke, call 911 for emergency medical care. 

Elevate Your Training as a Certified Personal Trainer

Working out safely is important in every season, but the stakes are often higher in summer. Keep this useful information in mind for your own workouts and when working with clients who might not know better. 

ISSA’s Certified Personal Trainer Program is a comprehensive self-paced and online course for becoming a skilled personal trainer. Wherever your fitness journey takes, ISSA certification is an excellent first step.  

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Institute of Medicine (US) Committee on Military Nutrition Research; Marriott BM, editor. Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington (DC): National Academies Press (US); 1993. 3, Physiological Responses to Exercise in the Heat. Available from: https://ncbi.nlm.nih.gov/books/NBK236240/

Brown, M., & Brown, M. (2022, May 12). The surprising benefits of training in the heat. Outside Online. https://www.outsideonline.com/health/surprising-benefits-training-heat/

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