The Ultimate Guide to Running in Heat & Humidity

Jason Fitzgerald
by Jason Fitzgerald
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The Ultimate Guide to Running in Heat & Humidity

If it were easy, everyone would do it.

As a runner, you’ve probably heard that line more often than you care to admit. But running in the heat is something nearly all of us have to do (and we rarely find it easy).

Unless you live in the Arctic, chances are you’ll have to tackle more than the occasional hot run. So why is it that running and racing in the heat almost never feel easy? And what can we do as runners to make the experience a little bit more bearable?

Last week, we heard from Under Armour resident clinical exercise physiologist Jeff Knight on how to prepare for races in hot and humid weather. Any runner can have a successful run in these conditions, no matter their skill level. Let’s take a deeper look at what runners face during the summer months.


Why does running in the heat feel so difficult?


Evolution has allowed humans to be well-suited to endurance running. When it comes to running in warm temperatures, our lack of body hair and highly evolved sweat system are significant advantages. As we perspire, our body is able to cool itself as the perspiration evaporates. Unfortunately, extreme temperatures, dehydration and humidity can all wreak havoc on the efficiency of this system.

When heat is compounded by humidity, the air is already saturated with water, and the sweat on your skin has no place to go. The dew point is another measurement tool that relates to humidity — this is the temperature at which the air becomes saturated with water. For runners, a dew point greater than 65° F will start to feel uncomfortable, and higher than 70° F will make even an easy effort feel challenging.

Although humidity and a high dew point will usually feel worse to the average runner, dry, hot air can also be problematic. In this case, your sweat may evaporate so quickly that you get dehydrated. As dehydration advances, your blood thickens, and your heart has to work harder to maintain circulation. This is one of the reasons runners experience something called cardiac drift — when your heart rate rises even though you are maintaining the same effort.

Heat-Related Dangers

While you should be aware of medical issues that can arise from pushing yourself too hard in hot weather, know that true heat-related emergencies are a rare occurrence. We’re here to help you run in the heat — not avoid it altogether! Run smart, stay alert and you’re unlikely to face any of these more serious problems.

Here are a few to watch out for:

  •   Heat cramps: These are simply muscle spasms caused by fluid and electrolyte losses. They can be readily addressed by proper hydration and reducing your effort level if you encounter them on your run.
  •   Dehydration: For most runners, up to 4% dehydration is safe, but anything beyond that can cause problems. Start your run hydrated, drink to thirst on your run and rehydrate well afterward.
  •   Heat exhaustion: Symptoms include dehydration, nausea, headache and a body temperature up to 104° F. Stop your workout immediately, and get to cooler temperatures before it becomes heat stroke.
  •   Heat stroke: This is extremely serious and can quickly become life-threatening. Symptoms include a body temperature of 105° F or higher, disorientation with clumsiness, confusion, poor balance and a lack of sweating. Get medical attention immediately!


6 Ways to Beat the Heat


It’s inevitable that running in the heat will feel harder than in cooler temperatures, but here are some ways to make the challenge a little less daunting:

1. Run by effort.

While this may seem obvious, it’s amazing how many runners still feel the need to stick to a precise pace better suited to cooler conditions. While proper pacing is important, it’s time to let go and run by feel when it’s hot. A heart-rate monitor can be a useful tool to help you gauge both easy efforts and workouts such as tempo runs, and it will also alert you to cardiac drift.

If a run is meant to be easy, throw the pace out the window and concentrate instead on your breathing and how you feel. Easy runs should feel easy, and in hot, humid conditions, this may mean that your pace decreases substantially. That’s OK. The benefits will come as your body begins to adjust, and you’ll be pleasantly surprised by your speed when cooler weather arrives.

2. Plan your route.

Summer is a great time to get off the roads and try out some local trails. No matter where you run, try to plan a route that is well-shaded, especially if you’re running around midday. Asphalt and concrete retain and generate a great deal of heat, so plan your route to minimize exposure to these surfaces if possible.

Unlike fall and winter, when you want the wind at your back on the way home, you may want to plan to run into the wind on your return route. Any breeze will help encourage your perspiration to evaporate, which will aid in the cooling process.

While many runners carry hydration systems on their runs, you can also plan your route near water sources that allow you to drink and refill your water bottle. Natural water sources like streams and lakes also tend to provide a cooler running environment, and jumping in for a quick soak can be incredibly refreshing on a hot day.

3. Timing is everything.

When it’s hot outside, timing your run appropriately can often mean the difference between a comfortably challenging workout and a suffer fest. Early morning is the coolest time of the day (especially if you’re willing to get out in the predawn hours), though humidity levels are likely to be higher. Some runners prefer heat to humidity, and vice versa, so experiment to see what time works best for you.

While a warmup routine is always advisable, you may want to minimize this to keep your body temperature slightly cooler before a run. For a race or hard workout, you may need to run less warmup mileage than you would on a cold winter day. Try to do any warmup routines in a shaded or air-conditioned area to avoid getting hot before you even hit the road!

Do your best to avoid the worst of the heat, but sometimes it pays to embrace it. If you’re preparing for a summer race where you know you’ll face challenging conditions, you may want to practice one run each week during the hotter part of the day to help you adapt. As always, use common sense and hydrate appropriately — you’re trying to acclimate, not run yourself into the ground.

4. Focus on nutrition and hydration.

While nutrition and hydration are always essential components of training and racing well, summer weather is less forgiving when you make a mistake. Newer research does show you don’t necessarily have to drink a predetermined quantity at prescribed intervals, pay attention to your thirst and the color of your urine. A pale lemonade color is ideal — dark urine may indicate inadequate hydration.

If you’re racing longer distances in the heat, practice your hydration and nutrition frequently. Food and drinks that are palatable in cooler weather may not settle as well in the heat, so be prepared to adjust your strategy if necessary. Drinks with electrolytes will help you maintain a proper balance of sodium and potassium relative to your water consumption.

“Precooling” is another strategy you may want to try, especially when running a marathon or ultra in the heat. While elite runners use elaborate gear such as cooling vests, try something as simple as eating a frozen Gatorade slushy before your race. This helps cool your internal body temperature and delay the inevitable rise as long as possible.

5. Stay cool on the run.

In order to stay cool on the run, start by dressing appropriately, in light colors and technical fabrics that will help wick sweat more effectively. Protect your eyes and face from the sun with a hat or visor and sunglasses. Continuous access to cold fluids is ideal, but too much hydration (especially in the absence of electrolytes) can pose its own set of problems, including hyponatremia.

If you’re running long, try to plan a route that either loops by your home or a convenience store with access to ice. Wet towels frozen the night before your run can be useful before and during a run. Dumping water on your head throughout your run can also be an effective cooling mechanism since it increases evaporation from your skin.

6. It’s all in your head.

While running in the heat has many physical ramifications, it’s important to take an appropriate mental approach as well. Adjusting your expectations at the outset will undoubtedly contribute to a more successful race or workout. Nonetheless, don’t always expect the worst. Pace yourself appropriately and you may be surprised by your performance, especially after you have given yourself adequate time to adapt to the conditions.

While studies show that it can take more than two weeks of training in heat and humidity to fully adapt, hot weather running can always be a positive training tool if incorporated with both restraint and optimism. Part of learning to race well involves coping successfully with discomfort, and running in the heat can be an invaluable learning tool.


Reap the rewards!


As you continue to practice running in the heat, your body does some amazing things to adapt. You’ll become more efficient at dissipating heat and regulating your core temperature. Over time, your sweat gets less salty to maintain a proper electrolyte balance, and your body learns to sweat at lower temperatures to jump-start the cooling process.

Train your body and brain, and you’ll be headed toward new PRs in the fall.

About the Author

Jason Fitzgerald
Jason Fitzgerald

Jason is the founder of Strength Running, a USA Track & Field certified running coach and 2017’s Men’s Running’s Influencer of the Year. Learn more about how he can help you run faster.


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