Depending on where you live in the world, there are likely seasons where you are consistently running in hot weather. For runners in the northern hemisphere, the summer months can bring about not only high temperatures but also high humidity.
Running in the heat poses safety and performance challenges for your running workouts.1Che Muhamed, A. M., Atkins, K., Stannard, S. R., Mündel, T., & Thompson, M. W. (2016). The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat. Temperature, 3(3), 455–464. https://doi.org/10.1080/23328940.2016.1182669
In some cases, the risk of heat stroke or heat exhaustion outweighs the safety and potential benefits of running outside in hot weather, relegating runners to the treadmill, or some other form of indoor workout.
However, unless the temperatures and heat index are extremely high, employing some hot weather running tips can usually allow you to continue training year-round, even through the summer months.
In this guide, we will discuss how to run in hot conditions, including high humidity and high temperatures, the risks of running in the heat, and tips for running in hot weather to optimize performance and safety.
We will cover:
Let’s jump in!
Is Running In The Heat Safe?
I am one of those runners that loves the summer.
I hate cold weather, so I struggle to motivate myself to get in my winter training in cold weather, but I don’t seem to mind running in high humidity or hot conditions.
However, many runners I coach are quite the opposite, and summer running is a recipe for quickly overheating and worrying about some of the more serious risks of running on hot days, such as heat-related illnesses, dehydration, or simply feeling unwell.
As a running coach, I would love to say that it is always safe to run in hot conditions, but the truth is that summer running requires safety precautions just as winter running can.
In the winter, we worry about hypothermia, in which the core body temperature can drop too low, or protecting the fingers and toes against frostbite.
With summer running, the risk of heat illnesses such as heat exhaustion, heat stroke, or even just heat cramps and dehydration are real risks that must be taken seriously.
It is important to have a summer running plan that involves checking the heat index before you head out the door for your workout, as well as maintaining an attitude of flexibility with your training plan in case it is too hot to run outside.2Heat Index Calculation. (n.d.). Www.wpc.ncep.noaa.gov. https://www.wpc.ncep.noaa.gov/html/heatindex.shtml
In full disclosure, I suffered from heat exhaustion myself once on a summer run. It was back in college when I was running high mileage and was more wedded to sticking with my training plan than listening to my body.
I ran 16 or 17 miles in high humidity in the middle of the day when the sun was beating down. I did a poor job with my hydration and I think my electrolytes also got depleted.
I finished the run and thought I felt fine, but as I walked up my driveway, I started to feel lightheaded, and my pulse was thready.
Honestly, the last thing I remember is feeling pretty dizzy and then being in an ambulance. My mom called the ambulance out of abundant precaution.
The EMTs rehydrated me, which helped bring my heart rate down, and they lined my arms and legs with cool packs as we headed to the hospital.
We probably could’ve dealt with the symptoms of heat exhaustion that I was displaying at home and worked on trying to lower my core body temperature quickly and hydrating back up, but I’m glad that she took it seriously, just in case.
Since that day, I have been much more careful about the time of day I choose to run with summer running workouts, and I always look at the heat index and the temperature.
High humidity can really affect how hot it feels outside, and the result is a rise in core body temperature when you run because the moisture content in the air prevents sweat from evaporating readily.3Che Muhamed, A. M., Atkins, K., Stannard, S. R., Mündel, T., & Thompson, M. W. (2016). The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat. Temperature, 3(3), 455–464. https://doi.org/10.1080/23328940.2016.1182669
It is also chiefly important to drink water, carry a water bottle, and monitor your heart rate when you are running in hot weather.
All of this is to say that heat exhaustion and heat stroke are real possibilities, and taking a cavalier attitude toward running in high temperatures can lead to unhealthy overheating.
What Temp Is Too Hot To Run Outside?
According to the Road Runners Club of America (RRCA), you should avoid running outside if the heat is above 98.6 degrees Fahrenheit and the humidity is above 70-80%.4Hot Weather Running Tips. (n.d.). Road Runners Club of America. https://www.rrca.org/education/for-runners/hot-weather-running/#:~:text=Understand%20heat%20index%20danagers%3A%20Avoid
For hot weather runs and humid conditions, it is important to know the signs of heat-related illnesses such as heat cramps, heat exhaustion, and heat stroke.
Signs of heat cramps include muscle cramps in the calves, hamstrings, other leg muscles, stomach cramps, diarrhea while running, or cramping as soon as you finish running.
Signs of heat exhaustion include heavy sweating, cold and clammy skin, dizziness, weakness, nausea, vomiting, and more.5Centers for Disease Control and Prevention. (2019). Warning Signs and Symptoms of Heat-Related Illness. CDC.
Signs of heat stroke can also include confusion, passing out, and other life-threatening symptoms.
The key to dealing with heat cramps or heat exhaustion is to try to lower your core body temperature as quickly as possible.
You should have a sports drink or electrolytes with water and move into the shade. Monitor your heart rate.
Getting into cold water can help lower your core temperature, but you don’t want to shock your system by jumping suddenly in. Either sip cold water from your water bottle or sit in a cool bath.
With heat stroke, you should seek immediate medical attention.
How Can I Prevent Heat Exhaustion While Running In High Temperatures?
Here are some tips for running in hot weather, including running in high humidity and running in hot temperatures:
#1: Always Carry Water
Dehydration is one of the biggest risks of running in hot weather.
Particularly if you are running in a dry heat, you might be sweating and experiencing a ton of evaporation such that you don’t even notice how much fluid you are losing.
While your clothes will get soaked with sweat when you are running in humid conditions, it is still important to work on your hydration.
It is important to carry water because you never know what water availability will be unless you are running on a track or in a park with water fountains.
You can carry a water bottle or use a hydration pack.
I like to freeze the water bottle before I head out so that I have cold water as it melts, but just make sure that you also have at least one water bottle with water that is ready so that you don’t have to wait to start your hydration.
If you are a heavy sweater, I suggest hydrating with sports drinks or at least electrolytes in your water, even if you typically just drink plain water and aren’t running super long.
The electrolytes will help ensure you do not dilute your sodium, which can happen if you drink too much water.
Hyponatremia is a potentially life-threatening condition in which your electrolytes, namely sodium, become too diluted. This risk is greatly magnified if you are guzzling water and not taking in any electrolytes.
In addition to having a higher sweat rate when you are running in the heat, dehydration will also increase the risk of heat-related illnesses and will increase your heart rate.6McCubbin, A. J., Allanson, B. A., Caldwell Odgers, J. N., Cort, M. M., Costa, R. J. S., Cox, G. R., Crawshay, S. T., Desbrow, B., Freney, E. G., Gaskell, S. K., Hughes, D., Irwin, C., Jay, O., Lalor, B. J., Ross, M. L. R., Shaw, G., Périard, J. D., & Burke, L. M. (2020). Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments. International Journal of Sport Nutrition and Exercise Metabolism, 30(1), 83–98. https://doi.org/10.1123/ijsnem.2019-0300
The thermal regulatory mechanisms are less effective as body fluid levels drop because your blood plasma volume decreases.
This means that your body has to conserve blood and cutaneous circulation, which normally brings blood to the skin to help lower your core body temperature, will decrease.
Additionally, dehydration will increase your heart rate. As your blood plasma volume decreases, your stroke volume decreases. This means that your heart rate has to increase to maintain cardiac output.
When your heart rate is higher, your workout will feel that much harder, increasing the rate of perceived exertion as well as the thermal strain and stress of your workout on your body.
#2: Prehydrate
If you are going to be doing a long run or you are a heavy sweater, hydrating before you go out for your run is essential.
It is often impossible to keep up with your sweat rate when you are running in the heat, so starting in a well-hydrated state keeps you that much ahead of dehydration.
#3: Pick the Coolest Time of Day
For winter running, it is often best to run in the middle of the day when the sun is at its highest, but the opposite is true for summer running.
Running before the sun comes up in the early morning will help spare you from running in the direct sun. However, note that humidity is often highest in the early morning. If you are more bothered by running in high humidity, you might prefer to run in the evening after sunset.
In either scenario, I recommend that runners look at the hourly forecast to plan the best time of day to run in hot conditions. Look at the heat index, which measures the air temperature with the heat and the real feel temperature with the humidity.
#4: Wear Light-Colored Clothes
I’m all for dressing modestly, but summer running isn’t the time to wear many layers.
To prevent overheating, you should wear as little clothing as possible from an appropriate/comfort standpoint.
This may mean running shirtless or wearing a sports bra and light running shorts.
If you do want to wear a shirt, choose a light-colored shirt such as white, pale yellow, cream, pale pink, or light blue rather than dark colors.
Dark colors absorb the heat of the sun, so they can contribute to increasing your body temperature.
Make sure you choose moisture-wicking, breathable material that will aid evaporation. Tight materials will trap sweat against your body and compromise evaporation, which is key to the cooling mechanism of sweating.
#5: Protect Your Skin
You should always wear sunscreen, a visor or running cap, and sunglasses to protect your skin and eyes from the sun.
Even when it is cloudy, the sun’s UV rays are more direct in the summer. Skin cancer is a real risk, and wearing sweatproof and waterproof sunscreen with SPF 30 or more can help reduce the risk of skin exposure to the sun’s harmful UV rays.
A visor or a running cap will keep the sun off of your face, which will also help prevent squinting.
#6: Run Indoors
I like to run outdoors year-round, and most of the runners that I coach would much prefer to run on the roads or trails than the treadmill as well.
When it is simply too hot outside, or you are concerned about the risks of heat-related illnesses, it is always better to run in a climate-controlled environment on a treadmill or swap your run for cross-training such as pool running, cycling indoors, or even something more low intensity outdoors such as hiking.
#7: Modify Your Training Plan
If you are following a training plan and working towards a half marathon, full marathon, or other summer race, I suggest looking at your week in advance and comparing it to the forecasted weather.
If you have a hard workout or long run planned for one of the days that looks to be the hottest or have the highest humidity, consider shuffling around your workouts before the week gets going so that you prioritize the hard workouts and speed workouts for cooler days.
You can save your rest days or cross-training days for the days with high temperatures and high humidity to minimize the impact of the hot weather on your training plan.
#8: Wear a Heart Rate Monitor
One of the best tips for summer running is to run by feel instead of pace.
The heart rate monitor doesn’t lie; it reports how hard your body is working to keep you from overheating and to support your workout in high temperatures and high humidity.
#9: Try Trail Running
Summer running is a great time to do some trail running.
Trails are generally protected from direct sun because of the overhead canopy from the trees. You may also look into shady bike paths or other tree-lined streets rather than open roads.
Running in the shade is sometimes 10 to 15° cooler than running in the direct sun.
#10: Be Patient
Most studies have found that it takes about two weeks for your body to acclimate to running in the heat.7Tyler, C. J., Reeve, T., Hodges, G. J., & Cheung, S. S. (2016). The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Medicine, 46(11), 1699–1724. https://doi.org/10.1007/s40279-016-0538-5
What about the cold? When is it too cold to run outside? Take a look at our next guide to find out:
What about sodium and other electrolytes? This is another major area you need to consider when running in the heat.
To be specific:
Get sodium tested and know how much you lose per litre of sweat
Track your sweat losses by weighing yourself before and after
Take appropriate amounts of sodium before, during, and even after the run
Hey Andrew,
That’s a neat little calculator!
Drop me a note if you’d like to do something with us on sodium/electrolyte levels during running.
Cheers,
Thomas
Hi Thomas, yes, would love to work with you on something like that – could you email me? andrew at ironmanhacks.com
Thanks
Andrew