The first time I went running during a heatwave was probably during my time in the San Diego California area. I was 16 at the time and stayed at a home of an active marine soldier, so one day I joined him on a track through a barren desert and scrub landscape. There wasn’t really a lot of shadow, temperatures were maybe around 29C, my condition wasn’t really good so I took it a bit slower, and then suddenly I was alone in the wilderness.
Apparently, I was joined by a few stray dogs, who began softly barking at me, and I really had no idea what to do, so I just stood there, a moment which seemed endless, but then the marine came back for me. Not entirely sure if he threw a stick or made some gestures but we could continue the run without the doggy’s.
Today, I know that the body needs about 14 days to adjust to a new climate, and acclimatization depends a lot on your life style. For instance most people are used to heat their homes during the winter times, naturally their body is not used to colder temperatures, hence they require more cloths against the cold.
But if you do not heat, your body becomes more cold resistant, you save money, reduce your carbon footprint, you can even dress less if you want to.
Tips for running during a heatwave
The following tips are for professional runners, is not a health advice, and if you are new to running please let a doctor check your health status first, and start slowly under normal temperature conditions. As pointed out, a lot depends on how adapted your body is with acclimatization to either cold or warm temperatures (or ideally both).
As a general rule of thumb I can not recommend to run at temperatures above 30C, unless you prepare for an ultra marathon in the desert. Otherwise there is really no need to put this extra heat stress on your body. Temperatures are usually below 30C in the morning or late evening hours during a heatwave in the northern hemisphere, so plan accordingly.
However, temperature alone is not always the best metric when deciding when to go running, air quality – ozone levels, smog, traffic amount, wind, humidity, all these factors can make a run at 26C feel extremely uncomfortable and exhausting. Always adjust according to how comfortable you feel during a run, the last thing you want is to be exhausted after a run, so take it slow if needed.
I usually do not eat at all when I run after waking up, usually some coffee will do, if you eat during the day and plan on running in the evening, eat only little easy to digest foods. During the heat the body draws more blood into the skin parts of your body and less so is available in your stomach and digestive track, do not put extra strain here, you will run much more comfortable if you only eat light or nothing at all.
Always take some water with you on a run, with liquid you can always decide on the run if you go the longer track or opt for the shorter route, no matter what you are prepared when you can drink and prevent becoming dehydrated. Use bright, as in white clothes, wear a cap, it really makes a difference when running in the sun.
One more thing to note are the night temperatures, and specifically your home’s indoor temperature where you sleep. At night temperature above 20C the body usually still has to work harder to cool down, thus it is important to let the body cool down again during extensive heatwave conditions with high night temperatures. This also requires to take in enough liquids and minerals to compensate for loses from sweating.
Extra actions to improve heat tolerance
Sauna, or dancing in a hot club environment can really help to further acclimatize, it also helps to activate the removal of remaining body, especially belly fat.
Start slow at lower temperatures, as long you feel comfortable, after around two weeks you should be much more temperature tolerant, then you can look what fits you most, maybe you prefer morning runs only, but you can also run twice a day, depending how relaxed you managed to end your runs. The path is the goal.
Further reading: Das geheime Leben des Körpers in der Hitzewelle (German) An adaptability limit to climate change due to heat stress