Altitude Versus Humidity: Which Is Harder?

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The joys of trail running always come with a bit of suffering. It’s part of the game, from gaining altitude in high elevation to sweating through every layer on a humid run. The satisfaction of beating the elements draws many runners to enjoy the wilderness and green spaces that come with the sport.

However, a better understanding of what you’re up against will make you a better trail runner. Preparation helps you avoid injuries and make that next race a little bit easier by considering the climate and just how high up that hill you’ll need to run.

Before we go any further, it’s fair to say you probably have an opinion on humidity versus altitude and which one you’d rather suffer on. Which one is harder? Is there even a definitive answer? Let’s find out.

“I’m definitely more of that ultra-flat trail mindset. I’d rather be in the high heat, high humidity conditions, just having the experience in it,” says Patrick Reagan, a trail runner who lives in Savannah, Georgia. “I think it suits me a lot better because it’s what I train in every day.”

Reagan’s running résumé includes a win at the Javelina Jundred and multiple appearances at Western States. The Hoka-sponsored athlete manages to train for all of this living on the relatively flat Georgia coast. He’s also a coach who sees the impacts of the humid climate he calls home daily but still finds time to prepare for big mountain runs.

“In dry climates, it’s really difficult to prepare for humidity,” says Reagan. “Whereas I feel like it’s easier to prepare for elevation for me going up to a dry climate than it is for someone coming from a dry climate and coming down to race in the summertime in humid conditions.”

RELATED: Running in Humidity and Heat Is Tough. Here’s How to Make it Easier.

Reagan says it has to do with how our lungs handle humidity. Health professionals agree that humid air feels heavier, and lungs work harder to process oxygen. The more humid it is, the more your body struggles to evaporate the moisture on your body. In the end, this is what makes you feel hotter and sluggish.

You’ve probably heard of people visiting areas of high elevation, and how it takes your body time to get used to being so far above sea level, humidity works the same way. Studies show that getting used to a hot and humid climate can take up to three weeks for your body to adjust.

Of course, the other simple factor of humidity is that it’s hot. It causes runners to sweat more, so you need a better hydration plan to ensure your body is getting water and electrolytes. Staying hydrated is the key to avoiding muscle cramps and heat-related illnesses.

Replicating humidity in a drier climate is not easy. Reagan suggests trying to use a sauna to get used to dealing with more moisture. On the other side, Reagan says he finds gaining altitude not as tricky and focuses more on strength training mixed with knowing that he’ll be doing a lot of power hiking.

“I’ll roll the dice and hope that I’m just ready and I’m fit enough and patient in the high country,” says Reagan. “For an event like Western States, I sacrifice the first 30 miles of the run. I know that in the high country, I’m going to have to run very easy because I don’t have a ton of experience with elevation. So the closer I get to 2,500 feet or 4,500 feet in elevation, I know I can start to ratchet down the perceived exertion in the effort. But in the sections of the race that are above 6,000 feet elevation, I know I’m just at a disadvantage.”

Reagan believes where you do most of your training may be the key to beating humidity or altitude, and that one is only harder if you’re not used to handling it.

On the opposite coast lives Krissy Moehl, an accomplished Patagonia-sponsored athlete who’s run many ultras, including UTMB, Hardrock 100, and Western States in the same year. She also previously held multiple supported FKT (fastest known times), including Mount Rainier’s 93-mile Wonderland Loop and the 165-mile Tahoe Rim Trail. Moehl several spent years in Colorado before moving to Seattle, Washington.

“I love being above treeline, and it’s worth it to me to pay any of the high altitude struggles or whatever to get to be above treeline,” says Moehl on her preference for altitude over humidity. “If it slows me down, that just means I get to enjoy it more and be up there longer.”

Like Reagan, Moehl has used her position as a professional runner to coach others and keenly understands what the body goes through when pushed to extremes. However, she also knows that everyone can handle everything a little bit differently.

RELATED: 10 Rules for Altitude Training

“I feel like controlling the controllable is a pretty important piece,” Moehl says. “The things we can control are getting good sleep, being fueled well, and being hydrated. So if we go into a high-altitude situation where we’re super stressed, haven’t been sleeping all week, and are skipping meals, we’re not giving ourselves the best chance to deal with this other adaptation if our body’s already fighting these things that we could have taken care of.”

Running at altitude means dealing with thinner air, and just like dealing with thick humidity, your body works harder to get oxygen into your blood. The end result can leave a runner feeling fatigued.

Moehl says when she had high-elevation races, she could spend time at the race location ahead of the event, and, as studies show, the process takes time. She knows this is a luxury that not everyone has, with the average person not being a professional trail runner.

“There’s a lot more fancy equipment now than when I was training and racing for these things at a higher level,” says Moehl. “Get yourself as fit as possible. Don’t stress about what you can’t control. Going into Hardrock training in the Cascades, I was in the best shape I could be in, putting in long days and being out on my feet and knowing what that felt like and giving time for recovering.”

Both Reagan and Moehl are experts at their craft. They have first-hand experience that can only come when you push yourselves to the extremes as they have. However, do medical professionals agree?

“How geeky do you want this to be?” says Dr. Spencer Tomberg with a laugh from the Denver Health Medical Center. Tomberg focuses on emergency and sports medicine. He works with athletes firsthand in the hospital’s orthopedic offices, while also working on several racing events, including Global Limits, a seven-day ultramarathon in humid Cambodia and multiple high-elevation races in the mountains of Colorado.

“The two things that change quite a bit (at altitude) are the amount of pressure in the air and the amount of oxygen,” Tomberg says. “It’s actually not that there’s a lower percentage of oxygen in the air. There’s just so much less pressure that there are less molecules in general, so it’s hard to pull the oxygen into your body from there.”

From there, a few things happen to your body. First, you’ll begin to breathe faster to make up for the need for oxygen. This leads to runners also forcing more of their own carbon dioxide out. Believe it or not, you need that CO2 to help with your body’s acid-base balance and avoid becoming too alkaline. If you do, that’s when you can feel nauseous, fatigued and have increased dehydration. Second, the lack of oxygen causes your lung’s blood vessels to squeeze down, causing what’s called pulmonary hypertension. In short, less blood will flow through your lungs, the one organ you need to be working well right now.

Avoiding this isn’t easy, according to Dr. Tomberg, who says you need to experience it.

“The way to train is to slowly come up in altitude. That’s usually about a three- to four-day process, depending on how high you’re going to get,” says Tomberg. “If you’re coming up to Winter Park [Colorado] for a race, which is at 9,000 feet, and coming from sea level, Denver’s your only step in between that would get you to a place where you could acclimatize for a little bit.”

Sitting 5,000 feet lower than Dr. Tomberg is Doug Allen, a physical therapist with Florida’s Advent Health. Allen works in Orlando as an athletic trainer with Track Shack, a local running store and partner of Advent Health. He can feel the humidity every day.

“To be able to drop your core temperature, your body’s system is going to be more stressed than in a drier environment,” says Allen. “I think one way you can best prepare for it is to know that hydration is key. You need to do more electrolyte replacements, and your diet needs to be dialed in more. And so I think it’s really important that you are not only drinking, but you have to eat.”

Allen says the mix of heat and humidity can turn scary when you account for heat-related illnesses like heat exhaustion and heat stroke.

The Centers for Disease Control and Prevention and National Weather Service agree with Allen and have a breakdown of what to expect when your body gets too hot and when it’s time to call it off.

Allen says a little pre-run preparation can help you go a long way.

“We really need to think about your equipment,” says Allen. “Moisture-wicking and Dri-FIT equipment will be key. We don’t want to end up with unwanted blisters and collateral damage to keep you from running because of the wetness. When our skin becomes so wet, it becomes more macerated and can easily develop a blister or a tear that can sideline somebody.”

Besides the obvious risk of chafing, Allen believes the extra health risks that can prove deadly make humidity the trickier of the two.

“I’m going to go with humidity as being more potentially dangerous and harder to deal with,” says Allen.

He may be onto something, as doctors, including those at the Mayo Clinic, agree that altitude sickness is rarely fatal, as long as people take precautions. Another 2018 study determined that an actual number is hard to determine, and often high-altitude deaths were related to other issues like hypothermia and a person’s general well-being. However, Allen and Dr. Tomberg agree a lot has to do with the conditions you are used to.

“For me, it’s humidity. Humidity is brutal to me, but I think it has to do with where you are,” says Dr. Tomberg. “You have to give yourself time to adapt to either one.”

Like so many trail running debates, the best answer may once again be: “run your own race.” Or at least expect the conditions to be harder if your body is not used to the climate or environment. Whether you’re dealing with altitude or humidity, one of the primary answers to getting over the finish line may be as simple as preparation. Runners should familiarize themselves with not only the elements they will be running in, but also proper gear, nutrition and an emergency contingency plan. While the debate ends with most believing that humidity may be the harder adversary, both the heat and altitude should be respected to ensure an enjoyable time on trails.