A Runner’s Guide to Running in the Heat
Take marathon runners for example. When the temperature rises from 50 degrees fahrenheit to 60 degrees, marathoners slow by roughly 3-7% percent. That means a 3:45:00 marathoner could expect to slow by well over 5 minutes!
The reason heat is such a challenge is that when you run, your muscles produce heat. In fact, the enzymes in the energy production processes work best when the muscle temperature is slightly elevated above resting temperature. That’s why we “warm up” before a hard workout or race.
We sweat to remove muscle heat, but add environmental heat, and the body has to balance two things – the performance you want from your running and keeping the body from getting overheated. Frankly, the latter will always dominate. The brain’s top priority is keeping you alive. The body does its best to deal with the heat, but it can only do so much when your body temperature climbs.
Let’s examine some key strategies for running in the heat so you can deal with it as best you can.
Pre-Run
Daily hydration
A key way that the human body removes heat is to shift blood flow to the skin. Sweat glands release moisture on to hot skin, and as the sweat evaporates, heat is removed. The sweat itself comes from your plasma (the liquid part of your blood) so maintaining your plasma volume is key for the sweat process to work.
Daily hydration is critical when living and training in hot and/or humid environments in order to maintain your plasma volume.
Luckily, an easy way to monitor your daily hydration is via your urine color. Dark colored urine indicates you are dehydrated. Optimal hydration is when your urine is light yellow. This color chart shows the optimal color of your urine.
I also find that if I have to urinate once every one to two hours, my fluid intake is optimal to maintain hydration. It goes without saying that if you start a run dehydrated, you significantly increase your risk of heat illness.
What to Drink
“What do I drink?” is a common question. Outside of meals, I suggest water w/ electrolytes and/or citrus slices. Water alone is fine, but too much plain water may cause you to urinate out precious electrolytes.
A variety of electrolyte supplements (powders or tablets) are available that you can add to plain water. Experiment to see which one you like best.
Adding fruit slices to plain water is also a great way to get hydrated. Lemon, lime, and cucumber are popular choices but most any fruit can help you maintain optimal hydration.
Warning: Be careful of liquid calories and sugar in hydration beverages. Using sports drinks and other sugary drinks for your daily hydration should be avoided. From dental health problems to diabetes risk and weight gain, it’s best to limit sports drink use to during exercise or immediately after a run. That’s what they are designed for afterall, not continuous consumption.
I mentioned “outside of meals” for water with electrolytes. During your meals, you can focus on plain water since your meal has electrolytes in it.
Ultimately, the goal is to establish a daily habit of hydration. Find what works for you, keep a drink bottle at the ready, and use the urine color test and the frequency of your urination as a guide for staying hydrated.
What are electrolytes?
Electrolytes are minerals that have an electrical charge. They help with numerous functions in the body, especially muscle contraction. The main electrolytes you need are potassium, sodium, calcium, and magnesium. Fruits, vegetables and leafy greens are great natural sources of electrolytes, but electrolytes are also available as a supplement (powder, tincture and dissolving tablets).
Choose Your Run Time and Route
A no-brainer for hot weather training is to select the coolest part of the day for your runs. This is pretty easy for morning runners as the temperature is typically lower in the morning compared to the afternoon. However for afternoon runners, changing the normal training time is a must if you want to avoid the greatest decrease in performance.
That said, I used to live in Austin, Texas. The challenge there was that it was cooler in the morning but more humid. In the afternoon, it was hotter but less humid. Since I am a morning runner, I chose to tolerate the humidity, but I knew other runners who would wait till later in the day (usually 8pm or later) when it was less humid. It’s kind of a “pick your poison” deal, and you may have to experiment to see which is less impactful to your running.
Another strategy to stay cooler and safer when running in heat is route selection. Choosing a shady and preferably non-asphalt route reduces heat from the sun and paved surface. Running near waterways and low areas is typically cooler though sometimes more humid.
From a safety standpoint, never run far away from help in hot conditions. You never know when heat illness will strike, so keep your hot runs where you can easily get help if you need it. An ideal route has access to fluids/water fountains, and you can get into air conditioning immediately if you get overheated.
I tend to run short loops, so I’m never too far away from extra fluids and help. I do not go for a long run on a remote trail when it’s hot. Best to stay close to civilization or have bail out options on longer runs in case I run into issues.
Lastly, don’t start a run when you are already hot. You want your body temperature low before starting a run in the heat. If you’re already hot, you’re likely dehydrated as well. The run will go poorly, and you’ll need extra recovery time.
Heat Index
I say “heat” which makes runners think only of temperature but temperature is only part of the story. Combine temperature with humidity and we get the heat index, which is the total head load while running.
As water vapor in the air (aka humidity) rises, evaporation of sweat decreases. Less heat is removed from the body and your core temperature rises.
The chart below from the US national weather service shows the heat index (a metric that takes into account the temperature and the humidity) with the associated risk of heat illness.
I currently live in the desert where the humidity is very low. It can be 90 degrees with only 10% humidity, and it actually “feels like” 85 degrees. With such low humidity, sweat evaporates rapidly taking heat with it. This is what people mean when they say, “It’s a dry heat,” therefore, higher temperatures are more tolerable.
Conversely, when I lived in the southeastern United States, it would be 84 degrees, but with 80% humidity, that would feel like 90 degrees. Sweat doesn’t evaporate as readily in humid conditions, so even though the temperature was cooler than where I live now, the heat index was higher and edged me closer to the danger zone for heat illness.
I like that most weather apps now provide the “feels like” temperature (heat index), which helps the runner better evaluate the risks of going for a run outside.
Gear up by stripping down
Compared to most sports, runners are lucky! Other than a good pair of shoes, you don’t need a lot of expensive equipment. Although you will need a few articles of clothing, made of comfortable and breathable cloth, for running in the heat.
Shorts
Choose elastic-waist shorts that fit comfortably. Many running shorts come with a slight cut at the side and are made from synthetic materials that dry quickly, breathe well, and allow for freedom of movement. Some styles feature built-in liners or briefs. The briefs replace your underwear and can help manage moisture. If you prefer wearing separate underwear, go with a moisture-managing fabric. If somebody tries to sell you a pair of cotton shorts, run! Cotton absorbs and holds moisture—the last thing a runner needs!
Also, be aware of chafing. Sweaty, salty skin chaffs quickly so make sure you have runner’s lube (google for available products) on hand.
Shirts/Tops
The one item making the most impact on your heat management is the shirt you wear. Once again, avoid cotton, which tends to absorb moisture and hold it. Because it’s slow to dry, a cotton T-shirt can get soggy and uncomfortable—and even cause chafing.
A “tech” fiber shirt or sports bra will do a much better job of wicking moisture away from your skin—keeping you drier and more comfortable in hot weather. There are lots of brand names out there boasting cooling fabrics, so you’ll want to look at the label for key terms like “moisture management” or “moisture-wicking.” Aside from the fabric, the style of top you choose is up to you but remember that light colors and a loose fit are a great choice in the heat.
Also, let’s remember that shirts are not just for wicking moisture but they also provide sun protection. Some runners wear long sleeve tech shirts for sun protection.
You see this a lot in ultra marathons where runners are exposed to the sun for extended periods. Hats, sunglasses and neck scarves are a great solution for sun protection.
And don’t forget the sunscreen. It’s not uncommon for new runners to come back with a sunburn because they didn’t think of sun exposure while running.
Carry Fluids
Runners think about carrying fluids on long runs, but when training in the heat, you should carry fluids even on short, easy runs. The fluid intake is not so much for the run itself as it is to get a head start on rehydration after the run. Drink as much as your GI system will tolerate while running and know that you are one step ahead on your rehydration post-run.
If you don’t like to carry fluids, then choose routes where you can stop at water fountains or even stash fluids along your route before you run.
How to Pick your Hydration Gear
The three main types of hydration gear are 1) hand-held water bottles, 2) a waist pack with water bottles or a bladder and 3) a backpack-style (aka hydration vest) bottle/bladder carrier.
Hand-held bottles are inexpensive and easy to use, but you have something in your hands which some runners don’t like.
I prefer a waist pack as they not only can carry your fluids but also your phone, nutrition, keys, etc. The negative is that they can bounce and some runners don’t like having something on their waist as they run.
The more expensive option is the backpack-type hydration carrier (aka a hydration vest). These are more stable but you have something that feels like a vest on, which can create chafing and interfere with heat loss.
Like finding the best running shoe, you simply have to experiment with each type to see what you like.
The fit should be perfect, bouncing should be minimal, and it should be easy to access the fluids.
Talk with other runners about which packs they like. I went through four of five waist packs before I found what worked best for me.
Final note: Prep your hydration pack well in advance and place it in the fridge to stay cold. The body likes colder fluids on hot runs, and the colder the fluid at the start of the run, the longer it will take for it to heat up and become unappealing.
Water Weight Loss
Before you get dressed for your hot weather run, weigh yourself (no clothes). Make a note of it. Then, when you return from your run and strip down, you know that the bulk of weight loss is due to sweat loss and that “water weight” needs to be recovered. You then hydrate frequently till your weight returns to pre-run weight. It’s a simple way to know when you’ve restocked your hydration.
One note: It usually takes a few hours to get your weight back, so have a daily hydration strategy that takes into consideration the depletion from your run.
Heat acclimation
While the body/mind cannot completely acclimate to heat, some adaptations take place that help you deal with it.
The changes take about 10 days, which is why the first hot days are really tough on you, but over time, the same heat doesn’t seem to affect you as much.
Adaptation number one is sweating earlier in runs. The body is trying to get ahead of the heat gain, so it starts sweating earlier. More blood is shifted to the skin, so it can evaporate the sweat taking heat with it.
Second, your sweat is more dilute. You essentially ration electrolytes, which are critical for muscle contractions that are lost during periods of heavy sweating.
Because you sweat earlier in runs, your body increases its plasma volume. More plasma volume means you have more fluid available for sweating.
Lastly, your brain gets used to the feeling of running in hot conditions. Your first runs in hot conditions are tough mentally, but over time, the same run doesn’t cause as many complaints from the brain as before.
Pre-Heat Prep
If upcoming training or racing are likely to be in hot conditions, you can trigger the heat acclimation by running in extra clothes or indoors in a heated room. Overdressing (wear extra clothes) causes an increase in your core temperature, and the body reacts by starting the acclimation process.
Sitting in a sauna can trigger the same adaptations. The bottom line is that raising your core temperature initiates the adaptations, so you can plan ahead if you’ll be training or racing in hot conditions.
I use this a lot with my runners who train in the winter for a spring race. A few sessions of pre-heat training does wonders in case race day is hotter than they are used to.
During the Run
The Danger Zone
All runners should know the signs of heat illness. Any hot run puts you at risk, so let’s walk through the signs of heat illness.
Heat exhaustion
Heat exhaustion is the first phase of heat illness. It is characterized by-
- Heavy sweating
- Cold, pale, and clammy skin
- Fast, weak pulse
- Nausea or vomiting
- Muscle cramps
- Tiredness or weakness
- Dizziness
- Headache
- Fainting (passing out)
For many, dizziness and the sensation of feeling cold are the first signs they feel of heat exhaustion. These symptoms are warning signs, and you must obey them. If you experience these symptoms, slow down your running, take a walk break, seek shade and fluids. Cut your run short and get into a cool environment ASAP.
Heat stroke
The next phase of heat illness is heat stroke, and this is a life-threatening situation. Heat stroke is characterized by
- High body temperature (103°F or higher)
- Hot, red, dry, or damp skin
- Fast, strong pulse
- Headache
- Dizziness
- Nausea
- Confusion
- Losing consciousness (passing out)
If you stop sweating, you are in trouble. Stop running immediately and seek help. Get cool as quickly as possible. It seems easy to avoid heat stroke, but since confusion is one of the symptoms, a runner with heat stroke may not make the right decision to stop. That’s why it’s good to have a running buddy, tell others where you are running, and choose a safe route where help is nearby when you are running in the heat.
Drink Up and Dowse Yourself! (Even on short runs)
Now that you’re knowledgeable about heat illness, let’s talk about ways to mitigate it while running.
I mentioned it earlier, but on hot runs, no matter how short and easy, you should hydrate. A few good swallows of a cold beverage every 10-15 minutes does wonders for keeping your core cool and staving off dehydration.
Place your water bottle(s) in the fridge overnight and add ice to them before your run. Make this a habit for each and every run. Trust me. It will make a big difference during and after the run.
Also when training in the heat, take every opportunity to dowse yourself with water. Cold water on hot skin takes heat away and makes the brain happier. Dump water on your head. Run through sprinklers. Any extra water on the skin assists the body in removing heat. And if you can, use ice in a bandana or stuff your hydration vest with ice. This works especially well in humid conditions where evaporative cooling is compromised.
NOTE: You may have noticed that some runners are genetically heavy sweaters. If that’s you, then it’s imperative that you focus on daily hydration as well as rehydration after running.
Pace? Heart Rate? Effort? Nope!
When training in the heat, the usual metrics simply don’t work. Your pace will be much slower, yet your heart rate will be much higher. Even easy runs will feel much harder than you expect them to be.
That’s why when training in the heat, I suggest you use breathing as your main metric. Breathing is the least affected metric when training in the heat, and luckily, you don’t even need a fancy running watch to use it. Use the “Talk Test,” explained below. If your breathing is in the right zone, you’re in the right zone (effort-wise) no matter the heat.
Note: This can be very tough for many runners given that pace and heart rate metrics are ubiquitous in running watches, which may or may not be giving accurate feedback.
The Talk Test Zones
- Endurance Zone – carry on a full conversation
- Stamina Zone – speak in 1-2 sentences
- Speed Zone – speak 1-2 words but definitely not a lot of talking
- Sprint Zone – grunts, moans, aack
Here is my full article on the Talk Test.
To see just how much you can expect your pace to slow, use the Heat Adjustment Calculator within the www.mcmillanrunning.com calculator. You’ll be amazed at how much you must slow down in the heat. This should make you feel more comfortable with slower running, but again, use breathing as your main guide.
Lastly, some runners genetically tolerate hot runs better than others, so just because your training partner may not be suffering as much as you in the heat, that doesn’t mean you’re not as fit, strong or “tough.” It simply means your genetics require that you take extra precaution when training in the heat.
High heat workouts to avoid
Another strategy is to move workouts around so that any workouts that are particularly challenging in the heat are moved to cooler days. For example, VO2max (aka speed) workouts and long runs are particularly challenging workouts in the heat. They generate a lot of body heat and thus put you at higher risk of heat illness. Move those workouts around based on your weather forecast. Or even hit the treadmill as a great option for avoiding the negatives of hot weather running.
You have Permission to Slow down
The bottom line is that you need to slow down when training in the heat, and that’s okay. Don’t chase pace or worry about heart rate. If you get hot, take a walk break. Walking generates much less heat than running, so it’s critical to take walk breaks if you feel you are getting overheated. Just getting out the door and getting in a slower and possibly shorter run is still good training when it’s hot outside.
Wind is Your Friend
A final tip is that if it is windy, start your runs running with the wind then finish your run against the wind. The headwind helps cool you as you are getting hot later in the run. New runners are always amazed at how much hotter a run with the wind feels. It’s a simple fact that you are often running at the same speed as the tailwind, so essentially, there is no air moving over your sweaty skin. Thus, no heat is being dissipated.
Alternatives
While you can acclimate somewhat to hot running, your training will always be compromised. If you have a big race coming up, then I highly recommend you do your most important workouts indoors where it’s cool. A treadmill or indoor track allows you to have high quality workouts that are just not possible when it’s hot outside.
All goal pace workouts, long runs and fast/intense workouts should be done inside. While I agree with the moniker the “dreadmill,” I believe it’s a great resource when it’s hot outside.
Here is my video on treadmill training.
All other runs (and just living in a hot environment) will trigger the heat acclimation we want, but doing the key workouts inside allows you the best of both worlds.
Racing in the Heat
Preparing to race in the heat is similar to preparing for a regular run, just elevated.
As with any training/racing in the heat, you must be optimally hydrated in the days leading into the race. Don’t wait until the last minute, down copious amounts of fluids, and think you’re adequately hydrated. Spend the last three or four days before a race focusing on daily hydration.
Once hydrated, the biggest challenge with a hot weather race is adjusting your expectations. As runners, we mentally struggle when we have to run slower than we know we could on a normal weather day. But, that’s just the way it is. In the heat, you must be careful, and the goal becomes how to optimize your result given the conditions.
I use two methods for goal setting for a hot race. First, I use the Heat Adjustment Calculator within the www.mcmillanrunning.com calculator as a way to get an equivalent performance in different conditions. For example, if you run 46:32 (7:29/mile) for 10K on a normal weather day but are going to have to race in 80 degrees and 40% humidity, then the heat adjustment calculator says a 47:53 (7:42/mile) time is a reasonable goal.
Second, if it’s an early season race where the athlete has not been exposed to any warm weather (like for a spring marathon coming off of training in the cold of winter), then I go more conservative with the goal. I might suggest we shoot for 48:15 in the 10K race.
If it’s later in the season and the runner has had some exposure to warm weather, then the adjusted performance of 47:53 is usually a good starting goal. I also determine whether the runner is a good “hot runner” or not. If not, then I’m even more conservative with the goal. A runner who is less affected by the heat, can typically stick with the adjusted race time from the heat adjustment calculator.
Once you’re hydrated and have an adjusted goal, it’s all about race day strategies to mitigate the effects of the heat. The first tip is to stay cool as long as you can. This keeps your core temperature lower. Stay in air conditioning as much as possible before the race. If you have to be outside in the heat, seek shade and wear an ice vest to keep your core temperature lower and wrap yourself in cold towels. Anything you can do to keep your core temperature lower before starting the race is helpful.
Because the goal is to keep your core temperature low, your usual warm-up should be modified. Do as little as you can yet still feel race ready. For me, I tend to cut my normal warm-up in half and focus more on my pre-race strides rather than an extended period of jogging like usual.
During the race, take every opportunity to dowse yourself with cold water. Even in a short race like a 5K, I’ll grab water and dump it on my head. For longer races, it’s about hydrating and dowsing. Again, cold water on hot skin takes a lot of heat away.
Follow your normal fueling/hydration plan for longer races BUT as it gets hotter and hotter, dilute your fuel more and more. The GI system gets dehydrated in hot conditions and won’t tolerate concentrated fuel like it would in normal conditions.
If you normally take a get every 45 minutes and follow that with water, in hot conditions take half the gel, follow it with several sips of water (sip and go, not grab and gulp). Wait a few minutes then take the remainder of the gel and follow that with more water.
Adjust Again
You can pre-plan your fuel/water adjustment as described above, but you never really know how you’ll feel till you are in the race. That’s why you must keep an open mind and stay attentive to any symptoms of heat illness.
I had to do this in my second marathon. I ran the very first Rock ‘n Roll Marathon in San Diego. The race was held in June to capitalize on the ocean fog dubbed, the “June gloom” that happens at that time of year. There should have been ideal racing conditions. However, the race start was delayed by 45 minutes and by the time we got going, the coastal fog had burned off. I recognized early on that my goal time was not going to happen. My focus then was simply to have a positive race despite the conditions. I finished much slower than my original goal, but what amazed me was how long it took me to recover after the race. The heat really did a number on my body, and that’s where I really learned to respect just how challenging heat is for the runner.
You must do the same when faced with a hot race. Accept that your goal time is irrelevant. The primary goal is to avoid heat illness and have a positive race. “Live to run another day” is my mantra, so I’ll happily slow down in hot races to make sure I don’t get overheated and risk future training.
Post-Run
Once you finish a hot weather run, it is imperative that you cool down quickly. Lowering your body temperature reduces internal stress and shortens recovery time.
Fun ways runners get cold quickly:
- Drink ice cold liquids. Always have a cold drink ready for when you finish your run. Cold liquid in your digestive system immediately begins to reduce your core temperature. Never start a hot weather run without a cold beverage ready to drink immediately afterward.
- Get into an air conditioned environment immediately. This can be the A/C in your car or your house, gym or office. Just get out of the heat and into a cold environment. Sit in front of a fan so the cold air can move across your hot, sweaty skin. Loads of heat will be removed, and your core temperature will drop quickly.
- Another great way to cool down quickly is to get into a pool or cold bath. Immersion in cold water removes heat quickly, and you’ll immediately start to feel better. Just regular cold tap water is enough to help remove heat from your body so run a bath before your run and get into it immediately after. A cold shower works too.
- Before you head out for your run, you can put wet towels in an ice chest or a freezer, so when you return from your run, you can wipe down with a cold towel enhancing the removal of heat from your body. Cold towels and ice packs are an easy way to ramp up cooling. Some runners even put clothes in the freezer so when they return from a run, they can put them on to help cool their bodies.
- Formerly so expensive only elite runners used them, cooling vests (aka ice vests) are now readily available. Wear these pre-run to lower your temperature and likewise put on an ice vest immediately afterward to cool your body.
Rehydrate ASAP
Immediately after a run, drink at least 12 ounces of ice cold fluids. More is better as a big bolus of liquid triggers the stomach to empty faster and thus get the fluid into the intestines, so it can be transferred to the bloodstream.
Continue to drink till your body weight returns to pre-run levels and you are urinating once every hour or two. This can take several hours depending how dehydrated you are post run.
Did you know that while Gatorade says it’s a “thirst quencher,” it’s actually designed to keep you thirsty so you’ll keep drinking it. When choosing a beverage (or collection of beverages), choose a drink with electrolytes that tastes good. Post-run it’s all about frequent drinking.
Boost Your Rest
Lastly, add extra rest. The heat load is a big challenge to the body so schedule some rest time in the hours after a hot run. Headaches and lethargy are a sure sign you need to literally chill out.
Also, look ahead at your training schedule. Long or intense runs in the heat require at least one more day of recovery before your next big session. When training in the heat, it’s best to add more recovery and increase the time between challenging sessions.
Final Thoughts
Training and racing in the heat is the new normal for many runners. The strategies in this booklet can help optimize your training and racing. Will your performance be compromised by the heat? It’s likely, but these strategies will keep you safe from heat illness and help you get the most from your training and best possible outcome on a hot race day.
