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11 helpful tips for hiking and running in the heat

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trail runner in desert backlit by sun

As I write this, a record-breaking heatwave is gripping the planet — and all of us who are training for summer and fall hiking goals are probably feeling a bit desperate. Because how the hell do you finish an 18-mile trail run or hike 3,000 ft. of elevation gain in this heat without totally cooking your giblets? So in today's post, let's look at some practical tips for hiking and running in the heat.

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1. Know what to expect.

Hiking and running in the heat put extra strain on your body — particularly your cardiovascular system.

Unless you are very well acclimated to the heat, temperatures over 85 F will almost always affect your exercise performance. However, you may begin noticing declines in performance at temperatures as low as 70 F, especially when humidity is high. Fun fact: science suggests that the optimal temperature for running a marathon is under 40 F.

One of the major ways your body cools itself is by shifting more blood flow to your skin. To accomplish this, your heart beats faster and the blood vessels in your skin dilate. This means your heart is working harder while less blood is available to your working muscles.

Another way your body cools itself is by sweating. When sweat evaporates from your skin, the process draws heat energy dissipates out of your body and into the air. While this feels great, excessive sweating (especially over a period of hours) can lead to dehydration and loss of electrolytes (salts) that are essential to your body functions.

2. Expect to be slower in hot weather

Being in good shape and acclimated to the heat can help you perform better on hot days. However, even elite marathoners adjust their goal time and pace downward when racing on a hot day.

When you start hiking or running in the heat, take things slow at first! Decrease your workout time and/or intensity to account for the extra strain on your body. Listen carefully to your body as you exercise, and be sure to rest or quit for the day if you notice yourself getting exhausted or overheated.

3. Goodbye heart rate training, hello perceived exertion.

It's also important to note that heart rate training is less effective in the heat, because your heart rate will be elevated. When it's hot outside, forget heart rate zones and use Ratings of Perceived Exertion (RPE) to measure your intensity.

RPE is a 0–10 scale on which 0 represents rest and 10 represents all-out effort.

  • RPE 3–4: long runs/hikes, easy runs/hikes, aerobic base building workouts

  • RPE 6–7: lactate threshold intervals, tempo runs

  • RPE 8–9: HIIT, sprints, hill repeats, anaerobic intervals

  • RPE 10: strides

4. Understand the heat index.

Hikers in particular are probably familiar with the wind chill index, which helps you identify and prepare for dangerously cold weather conditions.

The heat index is the summer equivalent. It takes into account not only temperature but also relative humidity.

High humidity decreases the rate of sweat evaporation. This can make you overheat even at relatively low temperatures (the 70s and low 80s). High temperature combined with high humidity greatly increases your risk of heat-related illness like heat stroke, heat exhaustion, and muscle cramps.

Like the wind chill chart, the heat index chart is shaded to indicate the risk of heat-related illness.

NWS heat index

When planning your training for the week, check the forecasted heat and humidity conditions. Then check again just before you head outside. Consider adjusting your schedule or working out in the gym on days when risk of heat-related illness is high.

5. Start early — in the dark if necessary.

If you're not interested in acclimatizing to the heat and just need to make it through the occasional hot day, work out early in the morning. This is when temperatures are lowest and exercise conditions are most pleasant.

And if you've got a long run or hike planned, consider starting your workout in the dark with a headlamp. This will give you more time to exercise before the sun rises and the air and ground heat up.

Hiking or running in the dark may seem weird. But remember that many summit hikes and trail races will also require you to start before sunrise. Getting some "alpine starts" in during training will help you prepare mentally to get up and get going. These predawn hikes will also give you a chance to test your headlamp before the main event.

6. Take electrolytes for workouts over 60 minutes.

Electrolytes are salts that conduct electricity when dissolved in water. Your muscles and neurons rely on electrolytes to function. Electrolytes also regulate the movement of water in and around of your cells.

When you sweat, you lose both electrolytes and water. Drinking water without replacing electrolytes can dilute the amount of sodium in your blood and cause a dangerous condition called hyponatremia.

Hyponatremia signs include nausea, fatigue, headache, muscle weakness, confusion, and irritability. Seek medical attention if you notice these symptoms during exercise. Left untreated, hyponatremia can lead to seizures, coma, and even death.

The easiest way to prevent hyponatremia when hiking or running in the heat is to add electrolyte tablets or sports drink to your water.

If you use a hydration system and don't want to gunk it up, carry a separate bottle of electrolyte solution you can sip whenever you drink water.

7. Hydrate the right way.

Good hydration is always important for athletes, but it's especially important during hot weather. Some guidelines to follow:

  • Maintain good hydration at all times. Drink plenty of water throughout the day. If plain water bores you, add some fruit slices to your water bottle to spice things up.

  • Prehydrate. Two hours before your workout, drink about 16 oz. of water. Drink another 8 oz. about 15 minutes before your workout.

  • If possible, weigh yourself right before your workout and write down the number.

  • While hiking or running in the heat, take 2 to 3 large gulps of water every 15 to 20 minutes. If your workout lasts longer than 60 minutes, you should also consume some sports drink with your water.

  • After exercise, weigh yourself again. Then drink 16 to 20 oz. of water for every pound of bodyweight lost.

8. Consider an acclimation regimen.

Did you know you can change your body's response to heat? This is something to consider if you will be training hard throughout the summer. It's also a good idea if you expect hot weather during your goal hike or race.

To promote heat acclimatization, start with easy workouts in hot weather. For the first week, keep workout time and intensity low (RPE 3 to 4). Gradually increase the difficulty of your workouts as hiking or running in the heat gets more comfortable.

Within two weeks, your body should adapt to the heat. Changes include an increase in blood plasma, earlier sweating, less salt loss through sweating, and increased stroke volume of your heart. You will still probably be slower in hot weather, but you will feel less tired and overheated.

9. Find a shady trail.

Your choice of trail when hiking or running in the heat makes a huge difference! Shade creates a cooler microclimate near the ground and provides physical and psychological relief from the blazing sun.

To discover new trails near you, I recommend checking out the apps Hiking Project or Trail Run Project. Often, the run/hike descriptions will let you know how much sun and shade to expect.

10. Wear light-colored, loose clothing (no cotton).

When the weather turns hot, it's time to lose the leggings! Instead, try running in shorts and a loose, moisture-wicking top. Cool colors will reflect light, making you more comfortable in the heat.

If you you tend to chafe between the thighs when you run in shorts, look for a 2-in-1 short. The short tights underneath will provide some protection for your skin. Alternatively, carry a tube of Body Glide and reapply it frequently during your run.

11. Know the symptoms of heat-related illness.

Because running in the heat is tiring, it can be tough to determine when you've crossed the dangerous line into heat exhaustion or heat stroke.

Heat exhaustion

Signs of heat exhaustion include dizziness, fatigue, faintness, muscle cramps, upset stomach, and headache. Your skin will often feel cool and clammy, and you may look pale to others.

If you notice heat exhaustion signs, stop exercising and rest in a cool place. Loosen tight clothing and sip fluids. Get medical help right away if you are vomiting, as this can be a sign of a more serious condition.

Heat stroke

Heat strokeis a serious condition that happens when body temperature rises to life-threatening levels. Suspect heat stroke any time an overheated person shows signs of altered mental status (confusion, irritability, unusual behavior, seizures). Hot, red skin can also indicate heat stroke. Contrary to popular belief, some people who develop heat stroke during exercise continue to sweat.

Heat stroke is always a medical emergency. If a companion develops signs of heat stroke, call 911 immediately. Move the person to the coolest location possible and attempt to lower the body temperature by applying cold, wet towels to the skin. Alternatively, you can sprinkle the person with water and fan them with whatever is available.

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So there you have them. My 11 best tips for hiking and running in the heat.

Do you have additional tips? Comment below to share.

Originally published August 1, 2019.