Hot weather running certainly may not feel pleasant and your confidence may dip as your paces slow down – but summer running does not have to be miserable. Heat acclimatization for summer running can actually be beneficial for your training, both by making you more comfortable in warmer temperatures and by actually making you a strong runner.
Training in the heat and humidity can actually evoke similar physiological adaptations as training at high altitude. Your body is smart and adapts to applied stressors; that is, after all, why those long runs and VO2max intervals are so effective in training. The same principle applies to heat: your body changes your sweat mechanisms, blood volume, and ability to regulate core temperature.
As a result of heat acclimatization, you sweat more, your blood flow and plasma volume improve, and you can better regulate your core temperature. All these changes make summer running feel more tolerable; you likely will even notice that your paces begin to match your effort, rather than appearing slower than you feel like you are running.
Evidence even indicates that hot weather training will aid in your body’s ability to tolerate cold temperatures. A 2010 study published in the Journal of Applied Physiology found that an increase in maximum cardiac output as a result of heat training led to an average of a 5% VO2max when running in cooler temperatures. This means that summer running can assist in improving your running for fall races, even if you don’t notice faster paces at first due to the heat.
Tips for Heat Acclimatization for Summer Running
Women respond to heat differently.
According to Dr. Stacy Sims, women thermoregulate differently than men. At the 2018 Boston Marathon, women seemed to handle the cold rain better than men; conversely, women do not handle heat stress as well as men. Women tend to sweat less and start sweating later than men due to differences in vasodilation.
The important aspect for women to consider when running in the heat is your menstrual cycle. During the high-hormone luteal phase (the approximately two weeks between ovulation and menstruation), blood flow is lower and the overall body temperature is higher, making us female runners slightly more sensitive to the heat.
What does this mean for the female runner? Anticipate changes in your adaptation to running in the heat based on your cycle. You may be doing well with heat acclimatization and then struggle in the heat the week before your period. Don’t be discouraged if some weeks are harder in the heat – this may be due to hormones, not your fitness or acclimatization.
Get off the treadmill and get outdoors.
Heat acclimatization will not occur on the treadmill, especially if you retreat indoors at the first sign of summer. If you want to acclimate to running in the heat, you want to get outdoors and expose yourself to the warmer weather – especially in May or June, when the summer heat isn’t at its worst.
While some approaches such as using sauna will quicken heat acclimatization, these approaches should be undertaken with prudence and guidance from a professional such as a coach. Incremental adaptations made from consistently running outdoors may take longer, but the approach is safer, more comfortable, and allows you to maintain your normal training schedule.
Heat acclimatization takes approximately two weeks, although some studies suggest the process is faster in highly trained individuals. The process will be uncomfortable and unpleasant in those two weeks, but if you stick with it, summer running will gradually feel more tolerable.
It’s important to note that, much like any other stimulus presented in training, heat acclimatization can be overdone. Don’t go outdoors and run at noon every single day. Embrace cooler days if Mother Nature presents them and, if you have harder workouts on your schedule, try to do them on cooler days of the week. If the heat suddenly spikes, scale back your intensity or mileage for a week.
There is a point where the treadmill is safer. This will vary based on where you live and how well adapted you are to the heat (Floridians will be able to tolerate much warmer temperatures than Seattleites) so use common sense.
Focus on your perceived effort and breathing.
Perhaps the most challenging aspect of heat acclimatization is seeing your paces sharply slow down for the first few weeks of summer. After all, your body is working harder to pump blood to your skin to cool your working muscles, which increases your heart rate. As a result, you have to work harder to maintain any given speed – which is why most runners notice that their pace slows down 30 seconds or more per mile in the heat.
If you try to maintain your normal pace, every run becomes a hard run – and that simply is not an effective nor healthy approach to training. Instead, focus on your perceived effort on summer runs and accept that your paces won’t be the same as you acclimatize – or even until the temperature drops.
For easy runs, this means your breathing should be light enough that you can carry on a conversation and your effort feels comfortable and controlled. Heat acclimatization is most effective on longer duration (~60 minutes) runs at an easy effort (60% of VO2max) or shorter duration (30-40 minutes) runs at a moderate effort.
If you are doing any speed work during the acclimatization process, shift your focus from pace to effort. I like short fartlek runs and hill repeats for summer training, rather than intervals focused on hitting an exact pace.
In extreme heat, you may choose to complete only easy runs, depending on your level of fitness. Extreme heat is a stressor and can turn even an easy 60 minute run into a hard day of training.
Even though heat acclimatization is beneficial, you do not want to be reckless when it comes to training in the heat. Follow some common sense to minimize the risk of heat illness. Run earlier or later in the day, not during the heat of the day (and check out these tips to help you run in the mornings). Opt for shaded routes or even head out to the trails, since pavement can reflect heat.
Your four-legged running buddy requires a more cautious approach.
All these principles apply to human runners, not necessarily your dog, so be mindful that your four-legged running buddy will not adapt to the heat at the same rate. If you run with your dog, start with shorter bouts of running in the cooler hours of the day and, if possible, in the shade. Don’t expect them to adapt to the full heat as easily as you do.
When running with your dog(s) during summer, monitor them for signs of heat exhaustion, including excessive drooling, heavy panting, slowing down, vomiting, and confusion. Humidity can make their primary mode of cooling – panting – less effective, meaning that high humidity at even relatively “cool” summer temperatures can still be dangerous for them. Dogs are more sensitive to heat than we are; wouldn’t you be if you were running in 80-degree temperatures while covered in dark fur?
How hot is too hot for running with your dog? This article from Active suggests two tests. If the pavement is too hot that you cannot press your hand against it for 10 seconds or more, it’s too hot for your dog. If the temperature in Fahrenheit plus the humidity equals 150 or higher (such as 80 degrees with 70% humidity), it’s too hot.
For more essential tips on summer running, including hydration and sun protection, check out these posts:
Do you enjoy running in the heat or struggle in it?
How hot is too hot to run outdoors?