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The Basics of Heat Acclimation, or How Not to Hate Summer Running

It’s May in Central Texas, which means we’re already having 90 degree days and quickly heading towards 100. Having spent nine years in the state, I’ve had plenty of time to come up with strategies for dealing with hot weather running, but the annual spring warm up always gets me. There’s inevitably a week or two, usually in April, when the temperature and humidity start to rise and running feels pretty claustrophobic. But then, magically, my body acclimates to the heat, the outdoors doesn’t feel like a sauna anymore, and the high effort level I was feeling tapers off. I didn’t realize the benefit of this gentle transition until a few years ago when I went away in August for two weeks and came back to find myself struggling with my usual 80 degree, 6am runs. I had essentially de-acclimated and had to redo the whole process - a most unwelcome surprise! 


Whether you are gearing up for a steamy summer at home or preparing for a destination race in a hotter-than-usual locale, heat acclimation is an important concept to be familiar with. Our bodies are really good at thermoregulation - or keeping our internal temperature steady despite external changes. When it is hot, humid, or hot and humid outside, our bodies maintain this temperature by dissipating heat; they send blood to the skin to off-load heat and increase sweating, which leaves a layer of cooling moisture on our skin. However, your body needs some time to acclimate to more extreme temperatures, usually around one to two weeks. Once acclimated, you’ll start sweating sooner and your blood volume will increase - both of which are key in lowering your body temperature. Interestingly, the composition of your sweat also changes so that you lose fewer electrolytes. When I get out for summer runs, I usually heat up pretty quickly and then have a noticeable sense of relief once I start sweating (it feels to me like it happens all of a sudden), which allows me to get into the flow of the run. It’s fairly easy to notice when I start sweating sooner after that first week or two of heat. 


I do a couple other things as my body is acclimating. My pace naturally slows in the heat and I don’t make an effort to fight it - I know my body is working hard enough. I also start hydrating the day before I run, or “prehydrating”. In the winter, I drink water throughout the day and often have tea right before bed as my “official” hydration strategy. In the spring and summer, I start to add in electrolyte drinks the day before, particularly for long runs. I usually run long on Saturday mornings, so Friday afternoon I’ll drink one or two electrolyte drinks - Nuun is my favorite, but there are lots of great products out there. Nuun is a bit lower in salt than some other drinks, so it’s good to experiment and see what works for you; sites like The Feed offer sample packs so you can try different brands and flavors to find your favorite. Hydrating during the run, with both water and electrolytes, is also so important when running in the heat. Carrying a handheld bottle with electrolytes, scoping out water foundations along your route, or stashing water and electrolytes along your route before you run all work well! Hydration is critical to ensuring safe running in the heat; if not sufficiently hydrated, our blood volume and circulation are affected, as is the amount of fluid we have for sweating - blood and sweat being key components in our bodies’ cooling strategies. 


If you are traveling and running or racing somewhere hotter than your typical environment, Stacy Sims, in her book Roar, recommends traveling to your race location early, if possible, or training with extra layers on, or using hot yoga or sauna training. I recommend checking out her book for more details!

 

Even when you’re acclimated, I know a lot of runners who just don’t love running in the heat. I love a bit of warmth, but Austin summers can still wear on me. Here are a couple other strategies I use for getting through the many months of summer. 

  • End with a splash: Austin is lucky to have Barton Springs, a spring-fed pool that feels icy cold year round, and t's a great place to jump in after a run. Look for pools where you might be able to end your run, or jump in a cold shower for some immediate post-run relief.

  • Run early: The sun rises early in the summer, and runners rise even earlier. While it’s still warm, running before the sun is up makes a huge difference.

  • Lose layers: I typically run in just shorts and sports bra in the summer; a sweat logged tank top prevents the breeze from cooling the sweat on my abdomen. If you feel comfortable, lose layers of clothing. 

  • Block the sun: If you run in the sun, consider wearing sunglasses or a visor to block the sun from your face. I always feel much better when I’m not squinting.

  • Hit the trails: If you have a hard time letting go of pace, even in the heat, try hitting the trails. Pace becomes much more variable on uneven surfaces and you might be able to find more shade for your run. 

  • Cool your wrists and the back of your neck: When you stop for water, splash some on your wrists and the back of your neck - this helps cool your body down. 

  • Take a break: If you feel yourself getting overheated, take a walk break or stretch break and regroup.


A woman smiles in front of a swimming pool
Enjoying a post-run dip at Barton Springs!

Despite our best efforts, heat illness can still be a factor and it’s good to recognize the warning signs. Heat stroke is the most serious heat-related illness, according to the CDC, and happens when your body can no longer control its own temperature. Its symptoms include:

  • Confusion, altered mental status, slurred speech

  • Loss of consciousness (coma)

  • Hot, dry skin or profuse sweating

  • Seizures

  • Very high body temperature

If you or someone you’re with is experiencing these symptoms, get immediate medical care! Heat exhaustion happens when your body loses too much water and salt, and symptoms include:

  • Headache

  • Nausea

  • Dizziness

  • Weakness

  • Irritability

  • Thirst

  • Heavy sweating

  • Elevated body temperature

  • Decreased urine output

If experiencing these symptoms, work to cool your body (getting to air conditioning, drinking cool water, etc.) and get medical care. 

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