As Switzerland was blessed with some really hot late summer days this week I had the pleasure to run in close to 35° centigrade (95° Fahrenheit). As of course it’s possible to run in intense heat you should consider some things to not affect your well-being in a negative way.
Heat has a massive impact on your endurance performance and the cardiovascular system. Also the VO2max (the maximum amount of oxygen your body can absorb) is reduced by a lot. Your heart rate at the same level of intensity goes up exponentially when running in temperatures of more than 18° centigrade (64° Fahrenheit) as the following graph shows.
When you’re training for a run that is probably taking place in very warm conditions it’s a good idea to train a bit in the heat. Also if you want to run during summer and cannot run in the early morning or late evening you have to do some runs in the heat depending on where you live. As it is not necessarily bad to run in hot weather you still need to consider some things.
This is the most important! If you are dehydrated when running I guarantee you that you’ll have a really hard time to keep going. Also it’s harmful to your body in many ways. Drink 0.5 liters (17 floz) before you start your run preferably some sports drink like Isostar or Gatorade. On the run every 10 minutes you should take a good sip of sports drink but this can vary depending on how much fluid you lose with sweat. Also rehydrate at the end of the run. Especially in hot temperatures sport drinks are the better choice because they also fill up your electrolytes.
Try to wear as less clothes as possible. You need to get your body as much possibility to cool down and covering your skin doesn’t help for that. Wear the shortest shorts you have, light socks and a sleeveless shirt. Also use functional clothing that transport your swear away from your skin. If you’re not sensible for sun burn you can as well go without a shirt. But make sure to use enough sunscreen no matter the clothes you choose.
You can train in the heat but you don’t need to set new records. As described above very hot temperatures will dramatically decrease your performance. So don’t try to run your usual pace or keep up with you training plan and do intense training. Try to just jog slowly and look how you feel. If you have a heart rate monitor use it too stay at a moderate level of intensity.
Seek a road or trail that is mostly in the shade so you’re not exposed to sunlight during the entire run. I prefer a forest when available a dense one where barely a sunbeam comes through the trees. In there it is mostly a few degrees cooler. If you have some streams, lakes or fountains on the way it’s great to cool down with some fresh water.
If it’s too hot for a run you could go pool running to simulate the movements of running but your body is always in the cool water. This is also a nice endurance training. Of course swimming is a great form of cross training on hot summer days but riding the bike in the shade is nice to get a cool airflow to your body.