One Dirty Magazine

Running Slower in the Heat

Science proves that it's normal to slow down in the heat. Here’s how to keep it easy.

David Roche August 1st, 2017

Running Slower in the Heat Megan Roche keeping an easy run under control on a hot afternoon at Rancho San Antonio Park outside Cupertino, California. Photo by David Roche.

Summer is the season of overtraining.

Every year, when the temperature starts getting higher and the humidity begins to creep up, the coach in me begins to have little panic attacks. I’m not thinking about upcoming races, but about upcoming easy runs.

Why? Even after months of acclimation, running performance will still be negatively affected by heat and humidity. Many athletes struggle to recalibrate their easy effort for the heat of summer. Will my athletes accidentally go too hard when they are supposed to be recovering and building endurance?

Most of us don’t want to slow down as much as we must to adjust for hot weather—it feels like a sign of weakness, or even worse, fitness loss. But all else being equal, if your easy pace stays the same even as the conditions go from slightly balmy (i.e. California in summer) to oppressively swampy (i.e. Florida anytime), you will overtrain rapidly.


Anecdotal Evidence

One of my athletes, Amelia Boone (a top trail runner and obstacle-course racing champion), recently traveled from her home in California’s Bay Area to Long Island, a difficult trade anytime of year, but especially so during summer. On her last run in California, she ran eight miles with 1,200 feet of climbing at 7:40 pace and an average heart rate of 150 beats per minute, on a 66-degree morning. For her this was an easy day in the hills after a tough workout the day before.

On a similar run in Long Island (eight miles, 500 feet of climbing, 7:35 pace) in 88-degree heat, she averaged a heart rate of 162 beats per minute, with spikes up to 177 bpm. For Amelia—someone known to be a good hot-weather athlete—heat changed a recovery run into an unintentional workout.

My most striking experience with the heat/humidity buzzkill was during a run commute from my former office in Washintgon, D.C. in 2014. I was running at an aerobic heart rate of 153 bpm at 8:20 pace on a warm afternoon when a stiff wind blew through Rock Creek Park. Suddenly, as the trees swayed ominously, the temperature dropped nearly 30 degrees. Without any change in my effort or heart rate, I sped up by roughly two minutes per mile.


Related: The Basics of Heat Training for Running


Hot Weather Research

There is research to back up these anecdotes. A study in the journal PLOS One looked at 1.8 million marathon results and found that temperature was the most important variable predicting performance, with around a ten-percent drop in performance in hot weather versus optimal conditions. Other studies show similar performance decreases, magnified when it is humid.

A table complied by Runner’s Connect summarizes the science to lay out the stakes: dew point (a metric combining heat and humidity) as low as 60-65 degrees will impair performance two- to three-percent. Meanwhile, a typical summer dewpoint on the east coast—75-80 degrees—will impair performance 12-15 percent. Dew points above 80 degrees? They don’t even rank it.

This rapid decrease in pace relative to heat is caused by a host of factors, but the main culprit is increased blood flow through capillaries on the skin, for cooling, leaving less blood and oxygen for generating power.

However, the heat effect varies based on each runner’s body mass, physiology and acclimation status. Essentially, different people have different critical thresholds for the core temperature at which the body is forced to slow down substantially.


How to Keep “Easy” Easy

No matter how much you acclimate, or how fit you are, your performance will decrease in warm and/or humid summer environments. That is a hard pill to swallow for many runners. Isn’t summer supposed to be the time for fitness breakthroughs before big races?

As a result, many runners keep pushing, refusing to slow down as much as needed, often without realizing that they are lighting the fuse on a fatigue bomb. Every recovery run that’s a bit too hard shortens the fuse, until one day all that extra, unplanned stress will blow up in the form of illness, injury, burnout or one of countless other maladies.

How can you adjust your expectations to continue getting fitter when the weather gets hotter?


1. Check your ego at the door.

Guess what? Your physiology is the same as all of your fellow homo sapiens. All of us are affected by increased core temperature from hot-weather running.

Practice the mantra: “I am not slow because I am running more slowly. My easy pace is not a measure of my fitness.”

Prepare to have your easy pace increase by one-to-two minutes per mile in many instances. Take pride in your ability to show self-restraint. Most importantly, remember that “easy” is not a pace—it’s an effort. If your pace stays constant in heat, then you are actually going at a moderate or even hard effort. Moderate or hard running on easy days is how running progress stagnates and regresses over time.


2. Invest in a heart-rate monitor, or carefully calibrate your perceived exertion.

Heart rate is the most objective metric to account for external variables affecting running effort, including heat. For many of the athletes I coach, we use the Friel Method to calculate Lactate Threshold Heart Rate (LTHR) by taking the average heart rate in the last 20 minutes of a 30-minute time trial. For most athletes, around 85 percent of that number is a good cap for easy days (more experienced runners doing high mileage might be at 81-82 percent; newer runners a bit higher). You can also use a certain percentage of your max heart rate (usually 70-75 percent), or even the cruder Maffetone method of subtracting your age from 180 (which I don’t recommend unless you’re just starting out with heart-rate monitoring).

If you don’t believe in heart-rate monitoring, calculating effort is tricky but doable. Make sure that you aren’t looking forward to being done with your easy runs—it should feel like a pace you can hold for a really long time, maintaining conversations and singing songs. On a scale of one to 10, don’t go above four for purely easy recovery days and six for easy endurance days. And most importantly, slow down immensely on hills, since that extra stress can really make things difficult.


3. Make sure at least half of your running days are truly easy.

All year round—but especially during summer—apply the heart-rate or perceived-exertion rules for easy days at least half of the time. For example, if you’re running five or six days a week, three or more of those days must be easy.

On the other days, you can have at it. During summer, many athletes thrive on strides or slightly shorter intervals with longer recovery that let them go fast (maintaining or improving running economy) without getting burnt up by the heat. But, no matter what workouts you prefer, if you fail to give easy days the respect they deserve your body will come back to roundhouse kick you in the face.

Combine these strategies with heat-acclimation techniques, and you’ll stay healthy and happy during the swampy months ahead. With hot summer running, just showing up will lead to breakthroughs when it cools off. Don’t judge pace. Instead, focus on effort and patience.


David Roche runs for HOKA One One and NATHAN, and works with runners of all abilities through his coaching service, Some Work, All Play.

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22 Comments on "Running Slower in the Heat"

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This summer has been hot where I am located at and I have been quite slower on my pace and pretty embarrassed and I hope it is due to the heat and not myself. It’s been high 80’s low 90’s and I don’t have a heart rate monitor so I just go by feel.. it seems like anytime hills are involved when I’m already going pretty slow I still feel exhausted no matter what.

David Roche

Jen, you’re being smart to slow down! It’s hard mentally, but if you’re patient, you’ll be rewarded when it cools off. You rock!


This is the first time I have actively trained in the summer. Living in southeast Texas I am at the high end of the heat/humidity scale so have had to really adjust for the conditions. Doing so, I have been able to increase mileage as I have been training for a 50k in August.
Great article!

David Roche

Amazing discipline and perseverance!!


When using the «Friel Method for running» and using our Lactate Threshold (LT) to determine our zones. Should my easy day be at the zone «Aerobic Threshold» or at the zone «recovery» ? I’m a bit confuse.

My LT is 179 and it’s giving me those zones using that methodologie :
1. Recovery : Less than 151HR
2. Aerobic Threshold : 152 to 160HR
3. Tempo : 161 to 169HR
4. Sub lactate Thresold : 170 to 178HR
5. Lactate Threshold : 179 to 183HR
6. Aerobic capacity : 184 to 190HR
7. Anaerobic capacity : 191+ HR

Thanks and have a good day!


David Roche

Pascal, it was intentionally vague on that point since it varies based on the person (a beginner might be at AT, an experienced runner in recovery, but with lots of variation based on physiology and goals and total training volume). Basically, anything under 160 for you should be okay as long as you aren’t doing high volume (50+ miles per week). But it depends on your history!


Ok Thanks. That may explain why i’m not always able to recover from my workouts. My peak weeks were around 45 miles in 2017 (with 2 main workout and a long run). For 2018, I will probably go for one workout a week plus a long run with easy running day in between at zone 1 (an strides at the beg of season). Again, thanks for all the information you are sharing with us! I really appreciate it!

David Roche

Wonderful plan! Keep on rocking it!


Training in NC where it feels like 105 with the humidity is the best training I know to get me ready for altitude running. Nunns, Ice Water & staying on the shaded trails – its a love/hate relationship but it has definitely made me a stronger runner!!

David Roche

YES! It’s altitude training in disguise! Lots of extra blood volume to deal with the heat. Great job!

Ed godoy

I’m 70 and I’m running about 12 min miles here in fruita co, it normally around 85 to 90 degrees in morning when I run. I try to take it easy and drink lots of water

David Roche

Wondeful! Altitude is a whole other beast to deal with too. Great running!

Ken Michal

“Most importantly, remember that “easy” is not a pace—it’s an effort”
I LOVE this!!! Added to my inspirational quotes folder! Thanks!!

All Day!

David Roche

ALL DAY! You’re the best Ken!

Rachel Ragona
Fantastic article. This is my first spring/summer living near hilly(ish) trails and training regularly in 80-90 degrees. It’s kicking my butt and although I’ve been able to mix in the odd mile or so of marathon tempo running, the majority is closer to 10:30-11:30 pace. I was panicking about losing fitness till I read this! I’m training for AC100, so I’ve learned to “embrace the walk” and do my eating/drinking on the uphills to keep my HR under control. To keep some speed in my legs, I actually started adding in some weekly fartlek style track sessions; anything from 30s… Read more »
David Roche

Rachel, that sounds like the PERFECT approach! You are ready for AC100, have so much fun this weekend!

About that “slightly balmy” California summer…it’s a high of 104 over here in Davis. This is my third summer here and for the first time, I’ve tried embracing the heat instead of hiding from it and hating my life. It’s not only made me a stronger runner, it’s completely changed my perspective on living here. Instead of “Ugh, I have to bike in this heat to get to work,” I think, “Sweet, I can get in some extra easy heat training on my commute!” Plus, a great bonus to being forced to run slower is that I’ve started noticing things… Read more »
David Roche

Haha, love it! To be fair to TR, the “slightly” addition was me on the amazing editor’s objection 🙂 I didn’t want to come off as a soft Californian! You are rocking it, really admire that approach.

I recently moved to an island on the Caribbean (3 months ago) where temp is always above eighty, even throughout the night. I always run by HR, usually MAF effort. I have noticed my easy pace has gone from about 7:30 to 7:45 to about 9:00 min mile. It’s a hard pill to swallow but I think like you said, get rid of the ego. Do you think it is possible to acclimate and get my easy pace back to 7:30-8:00? I have also found speedwork to be a bear. I train with Jack Daniels Vdot methodology and have had… Read more »

One thing that often goes unappreciated is that if air pressure stays constant, that means that when water vapor goes into the air, there must be less of other gases in the air, most importantly oxygen. On a 95 degree day with 90 percent humidity like we are having in the DC area right now, that comes out to about 5% less oxygen in the air.

Richard Downing

There is a free app on Google Play called Heat Pace Adjuster that allows you to enter your desired pace (under perfect conditions), and it will give you the equivalent pace for the current heat and humidity/dewpoint. It can also be used “backwards.” Namely you can give it the pace you actually ran and it will indicate what that pace would have been under perfect conditions.

Larry Horton

I never try running in the summer cuz many reasons. Thank information you give, I had more motivation to be stronger in this summer!