Why Humidity Makes Running So Much Harder—and What to Do About It

One day in July, I woke up to a rare summer treat: a crisp 67-degree morning. Ready to take advantage of the cooler weather without battling the smoke, rain, or extreme temperatures plaguing New York City this season, I set out with high hopes. But within a few blocks, my optimism had evaporated, as the humidity left me struggling to maintain a pace that should have felt easy.

In the end, I cut the run short, feeling more than a little discouraged by my performance and the day’s turn of events. It was the sort of run you’d expect during a heatwave, not on an unseasonably cool(er) day.

To get a better understanding of what went wrong, and how to avoid another miserable run, I turned to the experts who explained why high humidity levels are so hard on the body and how to best adapt your training during the muggiest months of the year.

How Humidity Affects the Body

The main thing I wanted to understand was why my sticky Saturday morning jog wound up feeling as draining as a marathon.

So I turned to John Gallucci Jr., DPT, and CEO of JAG Physical Therapy. Gallucci is a physical therapist and expert in sports medicine, the associate chief medical officer for Major League Soccer, and has worked with professional athletes all over the Northeast, where humidity levels often impact training and performance.

“Humidity changes how efficiently the body can regulate its internal temperature,” he told me. “When we exercise, our bodies rely on sweating as the primary cooling mechanism, and the evaporation of sweat is what lowers body temperature.”

“In humid conditions, the air is already saturated with moisture, making it much more difficult for sweat to evaporate,” he explains. “Your body retains more heat, your core temperature rises faster, and your cardiovascular system must work harder to circulate blood to both the working muscles and the skin to facilitate cooling.”

In other words, humidity can turn an otherwise easy run into a much harder workout.

“For runners, this often translates into a higher heart rate, quicker fatigue, an increase in perceived exertion, and a noticeable decline in pace,” he says. “A run that would normally feel comfortable can feel like a much more intense workout in humid conditions, even if the distance and effort haven’t changed.”

Humidity’s Impact on Your Speed

One way to account for humidity’s impact is to adjust your pace accordingly. But how much slower should you actually run?

Chris Minson, professor of human physiology and co-director of the exercise and environmental physiology labs at the University of Oregon, told me there are “no specific pace recommendations that can be made as both heat and humidity can greatly impact athletes in different ways.”

However, at higher humidities (those upward of 75 percent relative humidity), he suggests slowing your average pace by at least ten seconds.

“Once [runners] are much too hot, it is hard to back off enough to recover, so it is better to start on the easier end,” Minson says.

Gallucci emphasized that humidity’s negative impact on the body doesn’t mean you can’t run outdoors when humidity levels are high, or even that it will always feel like a drag.

“The body can adapt to humid conditions over time,” he told me. “Your body is adept at getting used to the heat if you give it some exposure. Gradually training in warm, humid conditions allows the cardiovascular and thermoregulatory systems to become more efficient, improving heat tolerance in as little as one to two weeks.”

“However, even for those acclimated to heat and humidity, runners should respect the environmental conditions and recognize that humidity is a legitimate performance factor that isn’t a reflection of their conditioning,” he cautions.

Minson largely agrees, but says he prefers runners “only do some training in a humid environment and focus on good adaptation to heat.”

This approach, he says, will improve overall thermal tolerance, help lower heart rate and core temperature at a given exertion and environmental temperature, and reduce perception of effort. In the end, training in a combination of heat and humidity may help runners acclimate to humid conditions more quickly.

How to Run Smarter in Humid Weather

While Gallucci’s input—that humidity reduces the body’s efficiency, but you can adapt over time—was reassuring, I wanted more practical advice on how to adjust my training over the next few weeks of high-humidity weather here on the East Coast.

Steph Kessell, an Olympic marathoner and head coach at Runna, has trained in all sorts of weather and regularly works with athletes who run in extreme climates.

“Runners should adjust expectations around the pace of their session [during humid workouts],” she told me. “Hot and humid weather changes how hard your body has to work, so expecting the same pace you run on a cool day usually isn’t realistic. If you get the effort right, you’ll still get exactly what you need from the session.”

“Rather than chasing the numbers on your watch, focus on how the run feels and adapt your pace accordingly,” Kessell says.

Nadia Ruiz, a serial marathoner and running coach, says the best way to alter high-humidity runs is by focusing on RPE (rate of perceived exertion) or heart rate.

For example, if a ten-minute mile typically feels like a 5 out of 10 effort on a cool day, a runner might slow their pace in humid conditions to maintain that same perceived effort—or to keep their heart rate around its usual level for an easy run.

“This allows the runner to adjust their pace effectively based on how they feel or how their heart is responding,” she says.

Kessell and Gallucci emphasized the need for proper preparation and recovery surrounding high-humidity training.

“Recovery is a fundamental part of every single person’s training journey,” Kessell says. “It helps reduce injury risk and prevent plateaus during training, and is especially important when training during hotter conditions.”

It’s also important to keep an extra close eye on hydration.

“Hydrate consistently throughout the day instead of waiting until you’re thirsty, consider your electrolyte replacement during longer runs, and schedule workouts during the cooler morning or evening hours whenever possible,” Gallucci says. “Wearing lightweight, moisture-wicking clothing can also help improve airflow and cooling.”

Ruiz and Minson recommend wearing as little as possible in high humidity environments, and to choose lightweight, breathable, moisture-wicking clothing.

“There are some very good materials available these days, but realistically in humid conditions it is best to have more skin exposed to allow the best dissipation of heat,” Minson says. “This will particularly help if there is a breeze or as a person moves through the air. Anything on the skin can create a ‘microenvironment’ that would not allow the dissipation of heat through sweating as effectively as bare skin.”

The Bottom Line

At the end of the day, there’s no magic spell that will make those humid runs feel easy.

But it can be helpful to understand why these runs feel so much more challenging and to remember that one tough run doesn’t really mean anything.

“A slower pace in hot and humid conditions doesn’t mean you’ve suddenly lost fitness, or you’ll experience less of a benefit from that day’s training session,” Kessell says.

She tells runners to judge a session by whether they hit the right effort, not pace. The same training benefit can be achieved with minor adjustments—not unlike running in the wind or at altitude.

And just when you think you can’t take it anymore, remember what’s around the corner: fall training. As the weather cools and humidity levels drop, the work you’ve done on your overall fitness levels will start to show up, making fall and winter workouts (and races) feel much easier.

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