All winter you look forward to running in the heat. You’re sick of the cold. You want to feel the warm air on your skin, shed the layers, and enjoy being outdoors again. But that first run feels like you’ve stepped back in time. You tire easily, legs feel heavy, you can’t maintain your pace. You feel awful and think you’ve lost fitness. There’s no need to panic.
The science
Your body is doing more work. Your muscles and skin are fighting over blood. To keep your legs moving, your muscles need oxygen-rich blood. But to keep you from overheating, your body has to rush a massive amount of blood to your skin to dump the heat. Your skin is stealing that blood, so your heart has to pump much faster just to keep up.
To cool you down, you sweat. That sweat is drawn directly from the water in your blood. As you lose fluid, your blood becomes thicker, making your heart work even harder to pump it through your body.
Sweat only cools you down if it evaporates into the air. If it’s humid, the air is already full of moisture, so your sweat just sits on your skin. You keep heating up, but you can’t cool down.
So your body forces you to slow down on purpose. It’s hitting the brakes to protect your organs from overheating.
How to adapt
There are four main ways you can adapt to running in the heat:
- Time of day. Running in the morning or evening, staying away from the peak heat times in the day is ideal. When I’m on holiday I run before breakfast. There are fewer people around and the sun is up, but it’s not too hot.
- Effort v pace. Hot days aren’t days for PB runs; they aren’t really the days for intense sessions either. Unless you can get out early or late enough that the temperature is comfortable. Drop your pace, ease off on intensity. You are still building fitness because your body is working harder.
- Hydration. Seems obvious, but on shorter runs where you don’t normally take water, you should take it on a hot day. Hydrating before and after your run is also important. If I’ve run for over an hour, I take a hydration drink when I get home to replace electrolytes. If I’m going for a long run, I take fuel and hydration drinks with me.
- Kit. Wear light-coloured loose-fitting clothing and keep as much skin exposed as you can. This means you’ll also need sunscreen. I wear a baseball cap, but any light fabric that works well. You’ll likely want sunglasses too. You can get ones specially made for running or sports, so they stay on and don’t move around when you sweat.
Acclimatise
The first few days, or maybe the first couple of weeks, will feel tough. But if you stick with it, it will get easier. Think about it like you are building up to a new distance or just starting out. It’s the same process; your body takes time to get used to the new temperature.
Recover
You may need more time to recover, depending on the type of session you did. Give yourself more rest, try to get a little extra sleep, and don’t forget to refuel and rehydrate.
One thing to watch. The temptation after a hot run is to sit out in the sun but go easy. You’ve just put your body under heat stress, and too much sun on top of that is more load, not recovery. Find some shade while you cool down and be aware of how much time you spend in the sun for the rest of the day.
Enjoy your run
Summer running is fun, the sun on your skin, no rain, less clothing. There’s plenty to love. But, like everything, a period of adaptation is to be expected. Stick with it, the effort is worth it.
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