Exercising in the heat can feel brutal. Ideally, you’d avoid working out under the midday sun, but with climate change driving up global temperatures, even late afternoons can feel scorching. If you’ve ever hit a wall with cramping, nausea, or overwhelming fatigue, chances are dehydration—not just the heat—was to blame.
Why Hydration Matters Even More in Hot Weather
“When people tell me, ‘I just can’t train in the heat—it feels awful’, that’s usually a major red flag that they’re not hydrating enough,” says sports nutritionist Dr. Meghann Featherstun, founder of Featherstone Nutrition.
In hot conditions, your body sweats more, which ramps up the risk of dehydration. That impacts everything from oxygen delivery to your muscles to your body’s ability to regulate temperature. Monique Marcelino, Director of Athlete Research at the University of Connecticut, explains: “Every organ and cell in your body needs water to function. Without enough, your core temperature rises faster, your heart rate spikes, and your risk of heat illness climbs.”
Even a 2% drop in body weight from fluid loss can derail performance. Think cramping muscles, digestive distress (nausea, vomiting, diarrhea), dizziness, or even mental fog.
How to Hydrate Before You Exercise
Hydration isn’t just about grabbing a bottle of water as you head out the door. The American College of Sports Medicine recommends starting at least four hours before exercise, drinking about 5–7 milliliters per kilogram of body weight.
Yes, coffee counts toward fluid intake—but because caffeine is mildly diuretic, balance it with plain water. “Arriving at your workout already well-hydrated helps you avoid spikes in heart rate and body temperature,” says Dr. Floris Wardenaar, associate professor of nutrition at Arizona State University. “And it simply makes the whole session feel easier.”
Hydration During Your Workout
Waiting until you’re thirsty isn’t enough. “By the time you feel thirsty, you’re already heading toward dehydration,” Marcelino warns.
The National Athletic Trainers’ Association suggests sipping 200–300 ml of water every 10–20 minutes during activity. But sweat rates vary widely—your training partner might lose 1 liter per hour, while you lose 3.
The gold standard is a sweat rate test: weigh yourself before and after exercise (without urinating during), subtract the fluids you drank, and you’ll know how much fluid you lose per hour. Your goal is to drink enough so post-workout weight loss stays under 2%. For example, if you weigh 75 kg and lose 1.2 kg in an hour, you’ll need to drink a little over 1.2 liters during that time to maintain balance.
Don’t Forget Electrolytes
Sweating doesn’t just deplete fluids—it drains sodium and other electrolytes. And while most people are advised to cut back on salt, athletes working out in extreme heat need it.
“Electrolytes keep muscles, nerves, and organs working properly. Without enough sodium, the water you drink won’t be absorbed efficiently,” says dietitian Amy Ehsani.
Losing too much sodium can even cause hyponatremia, a dangerous condition that affects up to 15% of marathon runners. Early symptoms may be mild—dizziness, confusion, swelling in fingers or feet—but severe cases can trigger seizures or collapse.
Most days, a balanced diet covers your electrolyte needs. But during long, sweaty sessions, especially past the 80-minute mark, electrolyte supplements can help: think sports drinks, sodium gels, electrolyte packets, or salt tablets. Even flavor can help you drink more consistently.
Rehydration After Exercise
Finishing your workout doesn’t mean your hydration needs are over. In fact, experts recommend replacing about 150% of the fluids you lost, since your kidneys will start producing urine again and you’ll keep sweating for a while.
A good starting point is around 800 ml of water post-workout, then monitor your urine color. Aim for pale yellow—closer to lemonade than dark apple juice. If you’re not urinating regularly (about seven times a day), you’re still behind on hydration.
How to Drink Smart
Chugging a liter of water all at once isn’t the best strategy. “Most of that water won’t stay in your system,” Marcelino explains. Instead, spread your intake throughout the day. Large single intakes (more than 800 ml at once) can overwhelm the stomach.
Food can also help. Fruits like watermelon, peaches, strawberries, and cucumbers are water-rich and refreshing post-run. For electrolytes, small salty snacks like beef jerky or even a pinch of salt can do the trick—sometimes more effectively than tablets.
And yes, even chocolate milk works—it contains carbs, protein, electrolytes, and fluids, making it a surprisingly effective recovery drink.
The Bottom Line
No hydration plan can erase the discomfort of exercising in extreme heat. But smart strategies—preloading fluids, steady sipping during workouts, adding electrolytes when needed, and replenishing afterward—can keep your body safer, your performance steadier, and your workouts more enjoyable.
In hot weather, hydration isn’t just about drinking more—it’s about drinking smarter.
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