What Causes Heat Stroke and Exhaustion in Athletes?

As a youngster, I spent a lot of time camping during the summer. We were always told to drink a lot of water. If you get dehydrated, you get heat exhaustion... or worse! Heat stroke didn't seem like a pleasant outcome, so we drank up.

As the summer really starts to heat up, you're probably thinking the same thing about your daily run. If you don't hydrate, you get dehydrated. That, in turn, could lead to heat exhaustion or heat stroke - a serious setback for your training. Not to mention that severe heat stroke can end up being fatal.

It turns out, though, that hydration isn't the only key to health.

Research on Heat Illness in Athletes

Recently, the New York Time's blog Well shared a study about heat illness in athletes. The researchers were interested in why a bunch of tri-athletes got sick at a competition early in the summer, but few of them got sick later in the summer season.

Their research suggests that there are multiple ways for heat stroke to set in. These athletes weren't afflicted with the "typical" heat illness caused by dehydration. They over-heated for a different reason. Although the research doesn't provide a clear-cut explanation of how and why this happens, the underlying theory is pretty simple. And it has some important implications for your training in the Summer.

What Causes Heat Stroke?

Simply put, you overheat. It's normal for your body to warm up during exercise. But, if your core temperature rises too high, your body faces all kinds of nasty consequences. At some point, your brain and muscles fry and, well, you could die. Not so nice.

Your body is designed to prevent this from happening. The typical method of cooling the body is to sweat. The body perspires, the perspiration evaporates, and your body is cooled.

This system, however, can break down if you're dehydrated. You can't sweat if there's no water in your body! And this is what typically causes heat stroke in sedentary people. If you're out the blazing sun and you don't drink up, your body's sweat glands will shut down and you'll overheat. Not pretty.

However, the research shows that this is not what happens when trained athletes over heat. The triathletes featured in the study were still sweating and well hydrated when they were diagnosed with heat illness. The problem couldn't be caused by hydration.

Instead, their bodies were just generating more heat than they could effectively dissipate. No matter how well hydrated you are, you can only sweat and cool off so much. A high humidity level and high ambient temperature makes this process even less efficient.

The athletes, then, were over-heating because their bodies couldn't get rid of the heat quickly enough. They were slowly getting warmer until, after a pretty lengthy period, they succumbed to heat illness.

Can It Be Prevented?

The typical form of heat stroke - caused by dehydration - is easily prevented. Drink up.

The other kind - caused when your body heats up more quickly than it can cool down - isn't so easy to deal with. In fact there's little that you can do to voluntarily change the outcome.

One of the key findings of the research is that people become acclimated to the heat over the period of a week or two. If you're not used to exercising in the heat, you'll likely become overheated. After a few weeks of exercising in hot conditions, though, your body adapts. It cools you more effectively (maybe by making you sweat more profusely?), and you can exercise in the heat with less danger of heat stroke.

So What Should I Do?

First, stay hydrated. If you're out in the heat and not sweating a lot, there's something wrong.

Second, avoid exercising in the first hot days of Spring and Summer. If it's been a breezy 70 or 80 degrees all week and suddenly the temperatures jump to the high 90s... take a day off. Or, better yet, go out in the evening or early in the morning when the temperature isn't peaking. Over the next few weeks your body will adapt to the heat, but early in the hot season your body will be especially susceptible to over-heating.

Third, go out in the heat for controlled periods. If you avoid the heat at all costs (jog in the cool morning, stay inside and air conditioned all day), your body is unlikely to adapt to the rigors of exercising in the heat. So go out and run in the heat! Just do so in a controlled fashion. Short recovery runs are perfect for this. You're running at an easy pace - generating less heat than a hard workout - and you won't be out there long - reducing the comopunding effects of exercising in the heat.

Why Not Just Avoid the Heat?

Well, you could do that. But what if you have a race in the summer?

The triathletes in the study didn't have a choice. If they wanted to race, they were out in the sun. You could certainly avoid putting any races on your calendar for the summer... but it's also possible that some of those late Spring or early Fall races will be on surprisingly warm days.

As long as you give your body time to adapt to the heat, you'll be ok. Avoid the heat on your long one to two hour runs, but sweat it out for your short recovery jogs. After a couple weeks, your body will adapt to the heat and you'll be far less susceptible to heat stroke.