How Exercising in Hot Weather Affects Your Body

Whether you're training for a summer race, squeezing in a midday run, or doing outdoor yoga, exercising in hot weather adds a layer of challenge that goes beyond sweat. Your body has to work harder to stay cool and that effort can affect everything from your energy levels to how many calories you burn.

Here’s what actually happens inside your body when you exercise in the heat and how to stay safe, hydrated, and effective while doing it.

1. Your Body Sweats to Cool Down

Sweating is your body’s built-in cooling system. As your internal temperature rises, blood is redirected toward your skin to release heat, and sweat glands activate. As the sweat evaporates, it cools your skin and helps regulate your core temperature.

But there’s a limit. Excessive sweating without proper hydration can lead to dehydration, and if fluid loss becomes severe, your body may not cool itself effectively, increasing your risk of heat illness.

How to help your body stay cool:

• Drink fluids before, during, and after exercise

• Choose electrolyte-rich drinks if you’re sweating heavily

• Snack on high-water content fruits like watermelon or cucumber

According to the American College of Sports Medicine, even a 2% drop in body weight from fluid loss can significantly impact athletic performance and cognitive function.

2. Your Performance May Drop

Even seasoned athletes find it harder to maintain pace or intensity in the heat. That’s because your body is doing double duty: fueling your muscles and cooling your core.

Studies have found that when people exercise in high temperatures, they tend to overestimate their effort and reach fatigue sooner. In endurance activities like running or cycling, this often translates to shorter workouts and slower speeds.

3. You Might Burn Fewer Calories

It may feel like you’re working harder, but in reality, you may be burning fewer calories than you would in cooler conditions. The heat can cause you to scale back your intensity or quit your session early, which reduces total energy expenditure.

Also, any weight lost during a hot workout is mostly water weight not fat. Once you rehydrate, your weight typically returns to normal.

4. You’re at Greater Risk for Dehydration

When you lose more fluids than you take in, dehydration sets in and it can happen fast in high temperatures. Common signs of dehydration include:

• Headache

• Dizziness or lightheadedness

• Nausea

• Muscle cramps

• Rapid heartbeat

• Fatigue

If you notice these symptoms:

• Stop exercising immediately

• Move to a shaded or cool area

• Rehydrate slowly with fluids

• Seek medical help if symptoms don’t improve quickly

Severe dehydration or heat exhaustion can progress to heat stroke, a serious condition requiring immediate emergency care.

5. Heat Can Help You Relax In Some Cases

Not all heat is harmful. Warm environments can help relax muscles, ease tension, and support mindfulness practices like yoga or breathwork. Stretching in a warm room may feel easier, and gentle movement in a heated space can promote circulation.

That said, this benefit comes with caution: if your body temperature rises too much, it can counteract the relaxing effect and put stress on your heart and nervous system.

How to Exercise Safely in the Heat

If outdoor training or warm studio classes are part of your routine, there are steps you can take to stay safe:

• Dress smart: Lightweight, breathable clothing helps sweat evaporate

• Use sunscreen: Prevent sunburn, which reduces your skin’s ability to cool you

• Hydrate regularly: Drink water or sports drinks every 15–20 minutes during workouts

• Take breaks: Step into the shade or indoors every 15–30 minutes

• Pre-cool: Drink cold fluids or wear a cooling vest before starting

• Avoid caffeine or hot drinks: These can raise your core temperature further

A 2023 study in the Journal of Applied Physiology found that pre-cooling methods, like ingesting cold beverages, can prolong exercise time by up to 21% in hot environments.

Final Thoughts

Exercising in hot weather challenges your body in unique ways. You may not burn more calories, but you will sweat more, fatigue faster, and run a greater risk of dehydration if you're not careful. Knowing your limits, staying hydrated, and recognizing warning signs can help you stay safe and even enjoy the warmth when used wisely.

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