Beat the Heat (and Humidity): The Importance of Hydration in Hot, Humid Weather

Beat the Heat (and Humidity): The Importance of Hydration in Hot, Humid Weather

As a mid-Atlantic, East Coast runner, I DREAD the Summer. For months and months, there’s no escape from the sweltering heat and soul-crushing humidity. We are forced to endure it or be relegated indoors to the AC for a huge chunk of the year.

Neither option is desirable. Either way — It. Is. Miserable.

Summer presents unique challenges when it comes to staying hydrated during outdoor exercise, particularly if where you live is humid.

Heat combined with humidity can be a double whammy that leaves you feeling drained and sluggish from the moment you step outside — as if the air has no oxygen in it or like you’re trying to breathe hot water.


It’s essential that you have a plan in place to stay on top of your hydration and electrolyte levels, since fluid intake has a significant impact on regulating body temperature and overall performance.

In this blog post, we’ll discuss why exercising in the heat and humidity feels harder and share tips for adapting to the conditions to get the most out of your summer while still being physically active.

Why it feels like heat and humidity are sucking the life out of you

Our bodies dissipate heat by releasing water from our blood to the surface of our skin to be evaporated. That surface evaporation is how we cool off. It’s a pretty cool system.

But in the heat, sweating increases and that causes a reduction in your body’s water content — which reduces the volume of blood plasma. So, basically, prolonged or excessive sweating “thickens” your blood.

This dehydration from sweat loss without hydration replacement reduces your blood volume. This means there’s less oxygen getting to the cells of your body and your heart has to then work even harder to support you.

Even mild dehydration (a loss of only 2% of your body weight) can cause a significant decline in your running performance and it’s unnecessarily stressful for your heart.

So that’s what the heat of summer does. What about the humidity?

Remember that sweat evaporating from the skin is how we cool off. Well, when the air is humid, there is less sweat evaporation from your skin and therefore less cooling. So, as your body temperature continues to rise, your body works harder and harder to cool you off.

And as your body pumps more blood toward your skin to reduce your core temperature, there’s less blood flow going to your muscles, which means your muscles have less oxygen to work with.

Additionally, as if all that wasn’t enough, the longer this all goes on, the more energy (glucose and glycogen) your body is burning through. Because, yes, running in the heat and humidity actually does require more energy.

So, when running in heat and high humidity, you should expect your heart rate, body temp, sweat rate, and perceived exertion (how hard the run “feels”) to be higher than normal.

No, you’re not less fit now, your system just has to work harder in this weather. You can help your body out by replacing fluid loss and increasing your carbohydrate intake during long outdoor activities or intense exercise to keep your system well hydrated and well fueled which will fend off fatigue for longer.

How electrolytes help you stay hydrated

Electrolytes are minerals — such as sodium, calcium, potassium, and magnesium — in our blood, urine and other body fluids that play an important role in fluid balance in our bodies by moving water and nutrients into or out of our cells through concentration gradients (from high concentration to places of lower concentration).

Electrolytes are like little Ubers shuttling water and nutrients to cells where they are used for muscle contractions, heart muscle contractions, and lots of other important things.

In other words, electrolytes make it easier for water from your blood to get to where it’s needed.

When you engage in prolonged physical activity or continuous moderate to high intensity exercise, you lose electrolytes through your sweat.

In humid or hot conditions, you’ll sweat even more and therefore lose more fluids and more electrolytes. So it’s absolutely critical that we replace these losses or we’ll start to feel pretty awful.

How long does it take to adapt to hot, humid conditions?

When you first start running in hot and humid conditions, it will be quite stressful for your body. But if you keep doing it, you’ll adapt and those same paces and temperatures in those conditions will be less stressful.

The best guesses are that heat and humidity acclimation will take around 2 weeks if you stick with training through it. If you bag your training sessions or opt for the treadmill in the AC, those adaptations won’t be happening — they only occur when exposed to the conditions enough to force an adaptation.

The more (safe) exposure you have to being active in the heat and humidity, the better your body will be at cooling itself while keeping oxygen going to your muscles.

Tips for staying hydrated while outdoors this summer

Good hydration during exercise in hot and humid conditions is crucial for maintaining your performance and preventing dehydration.

Here are five tips to help you stay hydrated during your workouts:

Drink plenty of fluids throughout your day.

To stay hydrated during your workout, it’s crucial to start hydrating well before you begin and drink water all day every day. Unless you enjoy the feeling of lots of fluid sloshing around your gut while you run or hike, it helps to make sure that you’re drinking enough fluid throughout the day rather than waiting until you feel thirsty or chugging a bunch all at once right before you go.

Drink at least 16-20 ounces of water or a sports drink 15 minutes before exercising to prevent dehydration — especially if you tend to exercise in the morning. Overnight, your fluid intake was nothing or very close to it, so make sure you get water in before heading out and …

Bring a water bottle for longer outdoor activities.

Always bring a water bottle with you during your workout and drink water regularly even if you’re not feeling thirsty. Aim to drink 4-5 big sips every 10-15 minutes during your workout.

For hot, humid runs or hikes over longer than an hour, a good rule of thumb is to take at least 16-20 fluid ounces per hour. Going out without water and trying to power through is not heroic, it’s foolish.

Choose the right drink.

In addition to water, sports drinks can be an excellent choice for hydration during exercise. They contain electrolytes that help replace what’s lost through sweat and some carbs to keep your body fueled and fend off fatigue.

If you’re going to be active outdoors for more than 90 minutes, you should also replace electrolytes with your hydration.

Slow TF down.

Your body is working hard to maintain what might feel to you like a snail’s pace compared to what you’re used to. But your body doesn’t “know” paces, it knows effort. So, as long as you put the same effort into your summer runs, you’ll continue to improve even if you feel a lot slower.

Consider this your carte blanche AND coach’s orders to dial back the pace and focus on effort for the summer. Trust me, all that work will pay off in the fall.

When adjusting paces, the key is to look at the dew point, which is a measure of how much moisture is in the air. The higher the dew point, the harder it is to cool yourself down through sweating. Check out this calculation to ballpark your adjusted pace.

Take breaks when needed.

Don’t hesitate to take breaks when you need them during your workout.

Walking up hills on your run and resting in the shade on your hike for a few moments can help you cool down, ensuring that you can maintain your output throughout your workout. These are perfect opportunities for drinking water and/or sports drinks too.

There’s no shame in walking or resting a little to keep the effort down. You don’t get bonus points for killing yourself out there.

🛑 STOP whatever you’re doing and HYDRATE 💦 as often as necessary!

Good hydration during exercise in hot and humid conditions requires a little extra effort, but it’s essential for your health and performance. By following these tips, you can ensure that you’re getting the fluids you need to be well hydrated and energized throughout your workout.

Cheers🚰 and carry on, friends.

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Hi, I'm Alison

I’m the Founder + CEO of Miles To Go Athletics.

My own journey has taken me from always-injured-and-in-pain-farthest-thing-from-an-athlete in my 30s to ultramarathoner + competitive weightlifter in my 40s and beyond. So I firmly believe that athleticism is accessible to EVERYONE and is actually the key to better quality of life.

My team + I are here to help you stop putting your life on hold due to pain, injuries, and “getting old” and instead get back to the things you really want to be doing – like being active with friends & family, chasing bucket list goals, and feeling badass at any age.

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