Everything You Need to Know About Running in the Heat This Summer

by Jason Fitzgerald

Summer training ain’t easy. With skyrocketing temperatures, high humidity, and scorching sun it can feel like it’s impossible to get in a good run.

Running in the Heat

A long run or fast workout is hard enough. What about a RACE? Like a friend of mine always says: In the heat, I don’t compete!

Even if you just run easy and skip the hard workouts, how are you even supposed to just feel good when running in the heat and humidity of summer?

In the last few weeks, the runners I coach have said some funny things about running in the heat. My favorite:

“I just got back from my 8-miler, and it was BRUTAL. I couldn’t do the workout… my body just isn’t ready for 90 degrees “feels like 95″ at 6pm. I just tried to repeat to myself “I LOVE SUMMER!” while also being glad I wasn’t jumping over piles of snow.”

Training well through the heat and humidity of summer takes a careful approach that combines timing, gear, and an understanding of why exactly it’s so damn hard to run in the heat in the first place.

But of course, it will still be tough. A few weeks ago at the Heartbreak Hill Festival put on by Runner’s World, I was talking to another runner about a race she ran in Miami. She was lucky to meet Kara Goucher and Shalane Flanagan (two pro distance runners), who told her: “I’ll take running at altitude over running in Miami any day!

Even the pros hate summer running!

Instead of complaining about how difficult it is to run in the heat, let’s see how we can make the best of it. And maybe even make the fall our fastest season yet.

Why is it So Hard to Run in the Heat?

If you’ve read Christopher McDougall’s fantastic book Born to Run, you’ll remember that humans are amazing endurance animals for a host of reasons. We have:

  • A huge Achilles tendon that produces a significant energy return while running
  • A (mostly) hairless body and highly evolved sweat system
  • Big butts. I cannot lie: according to Harvard professor Daniel Lieberman, our glutes are “running muscles”
  • A special ligament that attaches the spine to the skull and keeps our head from bobbing as we run

Can you guess which adaptation here is impacted by running in the summer? It’s our incredible sweat system.

Perspiration helps cool us off because as our sweat evaporates from your skin, it takes heat with it. But when humidity rises, it reduces your body’s evaporation rate because there’s already so much water in the air. Soon, you feel overheated and have to slow down.

If you live in an arid place like Colorado where the humidity is low, a hot summer day can still wreak havoc on your training for two important reasons.

First, the dry air evaporates sweat from your body almost as quickly as you’re producing it so you can become dehydrated much more quickly. If you start a run slightly dehydrated or run long without any fluids, your performance will significantly decrease (and you’ll feel like death).

As you become more and more dehydrated throughout a run, your heart needs to work harder to pump your blood because it’s becoming thicker (among a few other reasons too). This is called cardiac drift: your heart rate increases over the course of a run even when the intensity stays the same.

Let’s not also forget the heat and sun, both of which increase your core body temperature. As soon as you start getting too warm, running will feel much more difficult. Your “Rate of Perceived Exertion” (RPE) will increase even if you’re running a pace that’s usually comfortable.

Less evaporation because of higher humidity levels, increased chance of dehydration, and a higher core body temperature means that you’ll have to run slower to maintain the same effort. An unfortunate reality of summer training.

The Dangers of Running in the Heat

Summer Running

This article isn’t meant to scare you. After nearly 16 years of competitive racing and running in the heat and humidity of New England and the mid-Atlantic states, I’ve never been seriously affected by the heat in any meaningful way. Neither has any of my teammates in college and high school – and we raced and ran very tough workouts in brutal temperatures sometimes.

But that doesn’t mean the dangers aren’t real. If you run too hard at noon in July, you might experience some type of heat illness. Here’s what you need to know so you can avoid these setbacks.

Heat Cramps: muscle spasms that are caused by large fluid and electrolyte losses from sweating. They can occur while exercising but also hours after your run. No need to worry, they’re not serious – but make sure you stay hydrated and get enough electrolytes with sports drinks or fruit like bananas.

Severe dehydration: we’re all familiar with dehydration. Up to a 4% loss in fluid levels from exercise is still safe, but any more than that and you may experience dizziness, fatigue, and even mental disorientation.

Prevent this level of dehydration by starting your run already hydrated (your pee should be a straw color) and replacing your lost fluids as soon as you finish running. You can figure out exactly how much fluid you’ve lost by weighing yourself before and after a hot run.

Heat Exhaustion: if you work out too hard in the heat, you may come down with heat exhaustion – a case of dehydration, headache, nausea, and a core body temperature of up to 104 degrees. It’s much more common in runners who aren’t adapted to the heat.

If you think you have heat exhaustion, stop running, get out of the sun, and cool down with a cold drink and preferably air conditioning. And next time, run earlier in the day!

Heat Stroke: Danger! Heat stroke is very serious since your core body temperature is probably over 105 degrees. Symptoms include disorientation with clumsiness, confusion, poor balance, and a lack of sweating. Immediate medical attention is required where you’ll be cooled with a cold bath, air conditioning, and cold liquids.

At the 1978 Falmouth Road Race, Alberto Salazar (two-time winner of the NYC Marathon) suffered heat stroke and collapsed at the finish line after fading to the 10th place. He was rushed to the hospital with a temperature of 107 (!) degrees and read his last rites in a tub of ice water. He recovered and went on to become one of the greatest coaches our sport has ever seen.

7 Tips to Beat the Heat

The heat of summer isn’t the time to run your hardest workout and biggest mileage weeks – unless you’re super careful.

Run by effort, not pace. Running in the heat is the perfect opportunity to work on the skill of running by feel. Instead of strictly following pace targets that you might normally follow, run by time and effort rather than distance and pace.

Run early. There’s no perfect time to run in the heat of summer. But the early morning hours offer the lowest temperatures and a break from the strongest hours of sunlight (even though the humidity will be at its highest).

Get off the roads! Asphalt and concrete absorb heat and radiate it back onto your poor, wilting body. The summer months are a good time to try more trail running. Bonus: you have to run a little slower on trails which will keep you slightly cooler and trails are usually shaded. Win-win.

Adjust your expectations. If the National Weather Service issues a heat advisory (when the Heat Index, a score that reflects a combination of both heat and humidity, is over 105 degrees) running fast or long will be difficult and dangerous.

Even if there’s no heat advisory, remember why it’s so hard to run like you normally do in summer weather. Maintain the same effort and don’t sweat the slower paces (see what I did there?).

Don’t wear dark colors or cotton. Gear matters in extreme conditions so dress appropriately! Synthetic fabric like polyester is used in most running gear these days – use it.

Start your run hydrated (and keep hydrating). Even though hydration has been overemphasized in the last decade (see Waterlogged by Dr. Tim Noakes), it’s important to hydrate well before and after your run. Unless you’re running more than 75-90 minutes, you probably don’t need to take any water with you. But learn what works for you.

Plan your run around water. I never carry any fluid with me on a run – even a 20 miler in the summer. Instead, I run by fountains in public parks where I can swig some water and stay hydrated. If you live in a dry climate, running through sprinklers can help you stay cool, too. And who doesn’t love frolicking through a sprinkler?

Running in the Heat Has Its Advantages!

With all the whining we do about summer training, it actually makes you a better runner. Running in the heat causes our body to acclimatize to the conditions and adapt:

  • Your body gets better at sending blood from your core to your skin, helping to dissipate heat
  • With all that blood rushing to your skin, your muscles now get less oxygenated blood. So to compensate, your body produces more (who needs blood doping?!)
  • The body learns to control its core temperature and it won’t increase as much after you’ve acclimatized
  • You start sweating sooner at a lower body temperature to improve the cooling process
  • Sweat contains less salt so you maintain the right electrolyte balance

All these adaptations improve your efficiency and make you ready to run even faster as soon as the heat and humidity drop in the fall. So embrace the heat and run through it!

Then again, there’s some evidence that suggests that summer training is difficult because you think it will be difficult.

Yeah, tell me that after I shuffle home from a track workout in the sun and I might throw you out of my living room window.

But, it’s useful to know that at least some of the drudgery of running in the heat is because of our brain. It may present a good opportunity to “train your brain” to be comfortable being uncomfortable.

When you do, you’ll be in a good position to run a lot faster this fall. Take advantage of the physical AND mental adaptations you’ve gained from a summer of uncomfortable running.

You might just surprise yourself at what you’re able to run in a few months!

Download the Summer Training Infographic!

I created a fun infographic as a reminder of how to stay cool when running in the heat this summer. Feel free to print it out or embed it on your own site.

Click here to tweet this infographic!

Running in the Heat

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