As a runner I’ve logged miles in the snow, rain, and wind—but there’s nothing I find more challenging than working out in humidity, especially in the hot, sticky weather that is the summer of coastal North Carolina. Each time I exercise outdoors, I come back red-faced, drenched with sweat, and breathing heavily despite just doing my regular route. What gives?
While exercising in the heat is always more challenging than in cooler days, combining higher temperatures with humidity makes the environment feel even worse. According to Emidio Pistilli, Ph.D., an associate professor of exercise physiology at West Virginia University School of Medicine, the reason it feels so much harder is because humid air is already saturated with water, so your sweat doesn’t evaporate as readily as it does in drier conditions—and it’s that evaporation that cools you off.
“If it’s not being evaporated, you lose that cooling ability of the sweat,” he tells SELF.
In humid conditions, your body also sends more blood to circulate through your skin in an effort to cool it down, therefore sending less blood to your muscles. This also increases your core temperature—compounding the temperature bump caused by exercising in general—and makes breathing feel harder. (Hot, humid air can also make breathing more difficult in people with asthma or allergies, since it can constrict or irritate airways.) This increase in core temperature can be pretty dangerous, as it can lead to heat exhaustion or heat stroke, says Dr. Pistilli.
All this doesn’t mean, though, that exercising outdoors during the summer is necessarily a no-go. In many cases, prevention can go a long way to not only making your workouts feel less terrible, but also making them safer. Here are some tips for working out in the humidity you should know if you want to keep going in the heat.
1. Hydrate wisely.
Drinking enough water is key to getting through a workout in the humidity. Dr. Pistilli explains that being properly hydrated before a run can help delay the impact of that humidity-related blood redistribution and rise in core temperature.
The “right” amount of water to drink varies, as everyone has a different sweat rate, according to Bryant Walrod, M.D., a sports medicine doctor at Family and Community Medicine at Ohio State University and team physician for the Buckeyes. For proper pre-exercise hydration, the American College of Sports Medicine recommends consuming 16 to 20 ounces of fluid about four hours before exercise.
During exercise, the ACSM recommends drinking regularly, with the intent of replacing the amount of fluids you lose through sweat. Weighing yourself before and after exercise can help you determine how much fluid you lose through sweat, which you can use as a guideline for fluid replenishment during workouts of a similar duration and intensity under similar conditions. The ACSM also recommends drinking to thirst during exercise, so if weighing yourself can be triggering, that guideline can help make sure you are hydrating adequately.
After you work out, you’re going to want to make sure you’ve replaced all the fluids you lost sweating (especially if you didn’t drink during). For regular exercisers who aren’t going super hard or long—say, a 30-minute jog—drinking to thirst afterward is a good rule of thumb, says Dr. Walrod. For these kinds of workouts, plain water should be fine to rehydrate you. But if you’re doing higher-intensity activities or workouts that exceed an hour, you may want to pair your water with carbohydrates and/or electrolytes, as in a sports drink, he says. (While carbs primarily help replace your blood glycogen stores during exercise, they can help with fluid absorption too.)
Pairing hydration with carbs and electrolytes like sodium and potassium is important for those who go hard or long in the humidity. That’s because drinking too much plain water pre- or post-workout could lead to a rare but more serious condition known as hyponatremia, in which sodium blood levels drop too low. This can cause nausea, headache, or confusion. While this sounds scary, it’s also unlikely to happen for the average exerciser, says Dr. Walrod. (There’s no exact amount of plain water that can cause hyponatremia during exercise, since it also depends on how much sodium you lose in your sweat, but the ACSM recommends maxing out at about 27 ounces per hour to reduce your risk. That’s why if you’re a habitual salty sweater in the heat—one sign of this is if you notice white crystals on your skin or clothing after exercising in the heat—it can be even more important to rehydrate with electrolytes, as SELF reported previously.)
2. Start slow—and keep your intensity low.
The good news about exercising in the humidity is that it does get a little easier over time. Heat acclimation occurs when your body adapts to heat stress, which can take at least seven days of frequent exercise, Dr. Walrod says. The more regularly you get out there, the more efficient the acclimation will be, though there will still likely be a benefit from less-frequent exercise.
So what should you do during this time? As you’re allowing your body to adjust to the hot, humid weather, Dr. Walrod recommends cutting back on the intensity and the duration of your workout. That can look like bringing your pace slower by a minute or so, and cutting the distance of your typical runs in half.
It may also be helpful to warm up in a nonhumid environment during this acclimation period—say, by trying this quick warm-up routine in the comfort of your air-conditioned home before stepping outdoors. While warming up outside may seem like a smart way to adjust your body to the heat, you’re actually raising your core temperature more than you need to, which jumpstarts the impacts of the humid environment on the body, says Dr. Pistilli.
Once your body is acclimated and you start to feel the effects of humidity less intensely, you can go closer to your typical duration and intensity, but you should still be mindful of the humidity and heat of the day. In other words, be ready to make adjustments.
“Take breaks and listen to your body,” Dr. Walford says. “If it happens to be humid, just try to go slower.” In these conditions, he believes your body should go 10% to 15% slower than your usual pace. Oftentimes your body will intuitively slow down to handle the change in the environment, so be mindful of what it’s telling you—and don’t try to overrule its message.
3. Time your exercise to beat the humidity.
There are two things to think about when considering your outdoor summer workout: the humidity and the actual temperature. The sun’s rays are strongest at midday, which can make the temperature feel hottest then. But relative humidity is actually highest in the morning when the air temperature is cooler and more saturated with water. It’s lowest in the afternoon, when air temperature is the highest.
The best way to schedule your workout, then, is considering a measure that takes both of these things into account. It’s called the heat index, which is what the temperature feels like when combining relative humidity with the air temperature, Paul Chase, Ph.D., an assistant clinical professor of exercise physiology at Ohio University, tells SELF. If the reading is over 90, that means you should proceed with caution, he says. In that case, especially if you had an intense exercise session on tap, you’re likely better off swapping it for an at-home or gym workout in the comfort of the air conditioning.
4. Always wear sunscreen.
Wearing sunscreen is not only important while exercising under the hot, beating sun to prevent a sunburn, but it also plays a role in cooling: Burned skin doesn’t cool as efficiently, according to Dr. Chase.
Sunburned skin is hot to the touch and already causes a loss of body fluids, so mixing it with exercise in a humid environment where you’re already facing an increased strain on the body isn’t the best idea. If you have a sunburn, wait for it to heal before you attempt to work out in this weather, and make sure you’re wearing SPF (at least 30) whenever you’re outdoors—even when you’re not exercising. (Don’t forget to reapply regularly too: usually every two hours, or as recommended on the bottle.)
5. Equip yourself with the right gear.
An old cotton T-shirt isn’t going to cut it while working out in the humidity. That’s because the material absorbs sweat rather than wicking it away, which doesn’t promote the evaporative cooling effect of sweat. Dr. Pistilli recommends investing in sweat- and moisture-wicking clothing that allows for better airflow and leads sweat to pool off your body, therefore helping with cooling. Dr. Walford adds that wearing lightweight clothing will allow for more exposure of the skin to air, which helps sweat evaporate.
For cardio sessions that exceed an hour, Dr. Chase says you could use a hydration pack or vest to help replace some of the water lost during the exercise. For exercise duration less than an hour, it usually isn’t necessary.
6. Look out for signs of heat-related illness.
Feeling light-headed or dizzy, or developing muscle cramps, can all be early signs of heat exhaustion, according to Dr. Walford. If you’re experiencing any of that, you should stop exercising, get to a cooler place, and hydrate as soon as possible.
In more serious cases, heat exhaustion can lead to heatstroke, which is a life-threatening condition that can cause brain damage, organ failure, or even death, if not treated. With this condition, your core temperature can exceed 104 degrees Fahrenheit. A telltale sign of heatstroke is when your body stops producing sweat, according to Dr. Pistilli, which can be hard to monitor if you’re already sweating and sticky. While he says you’d generally have to be exercising in the heat for a long time to see this happen, it’s still something to be aware of when you’re lacing up in the heat.
By staying mindful of potential warning signs for heat-related illness, and playing the preventive game by hydrating properly, wearing the right gear, and tweaking your routine, you should be able to make your hot, humid workout feel a little more bearable. And if you just can’t stand that stickiness? Don’t force it—you don’t want to start dreading your workout! We have a whole bunch of at-home workouts you can swap in for your regular routine until the coolness of fall rolls around.