Running in the heat can be challenging, as anyone who’s tried it on a Mediterranean holiday will tell you. It feels much harder than running in cooler climates, like in the south of England. But why is this, and could there actually be benefits to training in the heat?
Why Heat Makes Running Harder
When you run, your body generates heat, much like a car engine. To keep functioning properly, your body needs to stay cool. If it overheats, critical functions—like muscle contractions, brain activity, and the removal of toxins—start to break down. This is why running in the heat is so tough: your body is working overtime to avoid overheating.
How Your Body Cools Down
Your body’s main method of cooling down is through sweating. Sweat is produced by sweat glands, reaches the surface of your skin, and then evaporates, taking heat with it. The more you sweat, the more you cool down. However, there’s only so much sweat your body can produce because it depends on how much liquid (fluid) you have in your body.
During a long marathon, for example, you could lose up to 5 kilograms (about 11 pounds) of weight through sweating. That’s around 5 liters of fluid. Since your blood only has about 5 liters of fluid in total, the body has to pull water from other tissues to keep producing sweat and cool you down.
The Role of Heat Adaptation
This is where heat adaptation comes into play. When you’re not used to running in the heat, your sweat glands aren’t very efficient. They let both salt and water escape, which means the salt concentration in your blood doesn’t rise. Without that increase in salt concentration, your body can’t draw extra fluid from your tissues back into your blood. This leads to a drop in blood volume, making it harder for your body to deliver oxygen and nutrients to your muscles, which hurts your performance.
When you become heat-adapted, however, your sweat glands change. They go deeper into your skin and start reabsorbing salt back into your bloodstream as you sweat. This increase in blood salt concentration helps pull more fluid from your tissues into your blood, keeping your blood volume stable. With stable blood volume, your body can keep supplying your muscles with what they need, even in the heat.
The Benefits of Heat Training
So, training in the heat can actually improve your running performance by helping your body adapt to better manage fluid and salt levels. Your sweat glands become more efficient, your blood volume remains stable, and you’re better able to cool down while running, even in high temperatures. Additionally, being heat-adapted means you can tap into the fluid stored in your tissues, allowing you to keep going strong during long races without overheating.
In summary, while running in the heat might feel tough at first, over time, it can help your body adapt in ways that improve your overall performance, making you a stronger runner in any condition. As with any training adaptation, it is critical to do it slowly and over many months. Start by wearing longer sleeves in the winter rather than a t shirt, then maybe add in a jumper, and then in the summer start wearing longer clothing and over time you’ll slowly see an increase in what temperature you can run in and tolerate!
For those who are interested - the article below is from 1986 and is unfortunately behind a pay wall, but highlights the key points made above. You can also find a more scientific explanation here (http://christofschwiening.blogspot.com/2015/10/sweat-sweet-is-better-than-salty-for.html)