Much of the West Coast was overwhelmed by a heat wave this week, launching temperatures 20–30 degrees above average as the balmy waft of warmth struck states from Arizona to Washington. Temperatures hit 100° in San Francisco on Monday — the average for this time of year is usually 67°.
In the middle of all that suffering was Portland, Oregon, where temperatures reached 98° and the heat index drove the mercury only higher to a toasty 104°. It was on that very day of overbearing sun that I was scheduled to run with a local run club in town, as is tradition every Wednesday evening. I reluctantly laced up my shoes and walked the mile to our starting point as sweat crept down my back and quickly soaked my shirt. Children played in the local park’s fountain as others hid beneath any open square of shade.
The city was on fire.
During most run club events we’re given the option to pound out a 5k or 10k loop. But while the 10k route had always called my name, week after week, the sun was screaming a bit louder that day. I eagerly elected to run the 5k instead.
Quickly I noticed the sheer intensity of the elevated temperatures and the effect that it wreaked on my body. Muscles in my legs grew fatigued at only 2 miles into the run as my mouth went bone dry. Sweat had perhaps a moment’s interval to cool before it evaporated as the sun gave it little chance to remain on my body. I noticed that my shins were sweating — and that never happens. It was hot.
As I crept closer to the final leg of the 3.1 mile expedition, I began to think of those that ran in this weather for fun. I thought of the Badwater Ultra that passed through Death Valley on a 135-mile course with 8,300 feet of gain from Badwater Basin to Whitney Portal (Death Valley is home to the highest registered air temperature on Earth at 134.1°F). I remembered watching highlights of the Marathon des Sables, an ultra held yearly in Morocco that spanned six days and 156 miles as it snaked its way through the Sahara Desert. And then I found myself asking a rather on-point question:
What happens to your body as you exercise in triple-digit heat?
The simple answer would be “you sweat a lot.” But that answer was too simple. Instead I wanted to know what really happens to your body as it’s pushed and stressed under such extreme temperatures.
Let’s discuss the findings.
Related: We’ve Finally Found the Limit of Human Endurance
The Heat Index
It all starts with the heat index — the combination of the actual air temperature and relative humidity that form the perceived temperature felt by the body. For instance, an air temperature of 90°, when combined with just 60% relative humidity, will lead the body to feel as if it’s actually 100° outside, thus drastically increasing the risk of health-related illness. And while the heat index may not necessarily be harmful in itself, it is an indication of potential issues to come, as the figure illustrates below.
Because the body relies on its ability to sweat as a means of remaining cool, relative humidity (the amount of water vapor present in air) can drastically influence this necessary regulatory system. If the humidity is also high along with air temperature, your body faces added stress because sweat doesn’t readily evaporate from your skin, thus elevating your body temperature even higher.
Heat Illnesses
In nearly all cases, the main reason that runners experience heat illness is because of dehydration. There are three main stages of heat illness to be aware of, each of which occurs based on the severity of the individual’s dehydration status. The inability to replace lost fluids and electrolytes will only exacerbate the severity of the illness over time.
Heat Cramps: Heat cramps are one of the most commonly noticed signs of heat illness, often occurring on those hot Summer days after a long bout of exercise. They’ll lock up large muscles in the legs, abdomen, and arms due to the heavy loss of salt and water. And while heat cramps become less frequent with heat training, maintaining adequate hydration and electrolyte balance is critical to avoiding them in the first place.
Heat Exhaustion: As dehydration intensifies beyond the commonly experienced heat cramps, heat exhaustion may occur. Characterized by symptoms that include cool skin with goosebumps, headache, faintness, rapid pulse, nausea, and cramping amongst other signs, combating heat exhaustion requires spending time in a cool place while replenishing fluids. If symptoms persist despite these measures, immersing oneself in cold water or packing with ice/cold blankets may be necessary to aid in lowering core body temperature.
Heatstroke: The final and most dangerous stage of heat illness, heatstroke is the failure of the body’s temperature regulation system, causing body temps to rise beyond 105° at which point damage may occur in both the brain and vital organs (brain damage commonly begins around 107.6°). If left untreated, symptoms may worsen to include convulsions or seizures as the brain begins to shut down. Though far less common, coma and death may occur at the most severe stages of heatstroke.
How Do the Pros Do It?
As I finished the 3.1 mile loop and dug a hand into my bag, searching for a full Nalgene bottle, I continued to wonder how anyone could run a 10k in such conditions, never mind a marathon or ultra. Most bodies will react rather similarly when forced to run in grueling temperatures or high relative humidity environments. So how do the pros do it?
While modern and perhaps sophisticated tactics may present themselves that aid an individual’s ability to exercise in the heat, nothing beats classic exposure that, in turn, leads to adaptation. Much like exercising at higher elevations has the ability to influence one’s red blood cell count, and thus their capacity to store oxygen, running or exercising in the heat is ironically one of the easiest means by which one adapts to said heat. Slowing the bouts of exercise down, remaining hydrated, and even passive adaptation through the usage of sauna sessions are all proven tactics to ensure the next run in scorching temperatures doesn’t end with a cooked brain.
Insanity Helps
As it turns out, most people react rather similarly when exercising in record-breaking, triple-digit temperatures. We all sweat profusely, all quickly grow fatigued, and definitely all complain that it’s simply too hot outside. Failing to remain hydrated is often the single limiting factor that possesses the capacity to influence the body’s ability to sustain the exercise without shriveling up on the pavement.
But let’s make one thing clear: the people that willingly subject themselves to temperatures shooting upwards of 130° in deserts like the Mojave and the Sahara are different people. They do that shit for fun. So while you may only need a bottle or two of Pedialyte to get you through those hot conditions, one other trait doesn’t hurt either…
Sheer insanity.
