The Downside of Uphills, Heat and Altitude

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Starting out, most runners have a vision of the best training session. Think back to what you thought was good training. I know what I pictured. You’re pouring out sweat like a broken fire hydrant, with your hands on your knees, your vision blurry, and your mouth tasting like rusted pennies.

Essentially, it’s every motivational poster in every weight room applied to running. (Or at least it was for me, because I came to endurance sports from a failed college football career of a few comically ill-advised weeks).

“Pain is temporary, pride is forever.” “Weakness is a choice.” “I mask my insecurity with loud grunts in front of floor-to-ceiling mirrors.” (That last one may just have been me).

And that general approach of going really hard works for weight lifting. Metal is forged and fire, and all that. Running plays by slightly different rules, though.

Every hard aerobic effort puts systemic stress on the body through the stress hormone cortisol, while also subjecting the body to more impact forces for more time. Hard running training can be like playing with a fire inside your body.

Running and lifting aren’t totally different. Both involve periodization of efforts with recovery between. However, in lifting, low-level aerobic development matters less. So you probably won’t see an Arnold Schwarzenegger impersonator bench press a protein bar 500 times and call it a day, which is the equivalent of a pro runner jogging easily for a few miles.

Easy running leads to fitness breakthroughs by supporting aerobic development over time, but it’s where runners face extra risk. If your recovery day does not let your body recover, what happens? Lifters know the answer too—you stagnate if you’re lucky, you get injured if you’re not.

So easy running matters for fitness and long-term growth. That’s simple to understand and internalize. But what happens when “easy” is actually something else entirely? When easy becomes hard, training often does not lead to beneficial adaptations, and it can be tough to know why.

I had a rude awakening this past week. I was jogging along in Boulder, Colorado, smelling the flower buds on the trails and, the…other type of buds through town. It felt easy, more of a frolic than a training session.

Then I looked at my heart-rate monitor. I was going up some longer hills at 168 beats per minute, not too far off my lactate threshold. My easy was actually moderately hard.

Let’s play this horror story out. What would happen if I did that every day? If I was fortunate, I’d just kind of get tired and a bit slower over time. If I was unfortunate, the hardest interval I’d be doing all day would be getting out of bed.

It all gets back to power output. On flat ground or downhills, gravity is your friend, telling you nice things about your running and outfit and smile. On uphills, gravity is a bully sent to tell you that Born To Run was fiction and humans are actually evolutionarily designed to eat Fritos while laying in the shade. To overcome gravity, you have to increase power output.

To avoid the horror-movie ending, you can calibrate your effort using a heart rate monitor or some other way of quantifying perceived exertion. But for many athletes, it’s a bit more simple than that in practice. “Today, I run easy. Tomorrow, I run harder. The next day, I eat cheeseburgers.” If you take that approach, it’s essential to think about some of the variables that can cause your exertion to skyrocket while you think it’s still firmly on the ground.

Here are three times to make sure you slow down easy days. Each of them can be blessings for your training for the same reason they can be curses—they are harder, inducing beneficial adaptations if you give yourself enough quiet time to recover.


Trail runners face one big conundrum with training—our favorite runs involve hills, and hills are rarely easy. You don’t see that in Instagram posts of beautiful mountain vistas: “Getting to the top of this so I could take a selfie nearly sucked my soul out of my nostrils.” Hills can be soul-sucking no matter how fit you get.

It all gets back to power output. On flat ground or downhills, gravity is your friend, telling you nice things about your running and outfit and smile. On uphills, gravity is a bully sent to tell you that Born To Run was fiction and humans are actually evolutionarily designed to eat Fritos while laying in the shade. To overcome gravity, you have to increase power output.

A number of studies have looked at effect of treadmill gradient on oxygen uptake, and all that matters here is the obvious conclusion—it’s a lot more. And it might be even more than you think.

Stryd power meters approximate power output, and Strava’s Grade Adjusted Pace function tries to equalize pace over different terrain. It varies by individual physiology, but 12 minutes per mile at 10 percent grade is somewhere around eight minutes per mile on level ground (with variance based on input variables, like bodyweight).

To that eight-minutes-per-mile runner, 12 minutes per mile might feel exceedingly slow. If they fail to adjust their pace to keep effort steady, an easy day will get a bit harder. Do that over hilly running routes enough, and a trail runner that thought they were frolicking through daisies each day might find themselves frolicking into the doctor’s office (or at least getting slower).


If you’ve run in the mountains, you know that thin air makes everything harder. Reams of science back that feeling up. A 2017 report from the “International Journal of Sports Physiology and Performance” found that training at 2100 meters altitude (around 7000 feet) reduced running speed in 19 elite male distance runners by 5.8 percent during threshold sessions and 3.6 percent during VO2 max sessions. Even at 1400 meters, they were able to keep the same speed of easy days and race pace running, but it required a higher perceived exertion (and, one could assume, a higher heart rate).

A 2015 study in the same journal looked at top track performances from 2000 to 2009 and found that for middle- and long-distance runners, even lower altitudes can impair speed. Countless studies address the same idea—it’s harder to run when you feel like you are breathing through a straw, even after acclimation.

So at altitude, the key is to focus on polarizing training intensities. You can go hard (I will have some of my athletes do fast intervals on slight downhills to remove the running speed impairment). But you need to worship at the altar of easy days. Even after you acclimate over time, exertion will be substantially higher for most athletes at the same paces, so embrace the slow. You may want to keep your easiest days flatter, as well, since there is almost no running speed slow enough for steep climbs at altitude.


This is around the time of year when coaches everywhere hear a similar Greek chorus arising from training logs. “I was so slow and it hurt so bad and I think I am in such terrible shape.” It’s a self-inflicted tragedy akin to Oedipus gouging out his own eyeballs.

Usually, the coach can just tell them to look at the current weather. It takes very little heat to make a big performance difference.

A 2012 study in the journal PLoS One looked at 1.8 million marathon results from 2001 to 2010 and found that temperature was the biggest predictor in performance, with a 10 percent drop in hotter weather relative to optimal conditions. According to Runner’s Connect, dew point (a metric combining heat and humidity) as low as 55 to 60 degrees F can have minor negative impacts on performance. The heat effect can be explained by a number of factors, primarily increased blood flowing through capillaries for cooling, leaving less blood for working muscles.

Add a lack of acclimation to the mix, and it can lead to some tragic runs. One time, I was running in California in February, and it was an anomalous 78 degrees, 16 degrees above normal (everyone living in the Northeast can now open real-estate website Zillow and search Bay Area housing prices to feel better). I ran in the warm sun, and after six miles, my hands started tingling. Twenty minutes later, I found myself practically walking uphills as my heart rate wouldn’t come down. It doesn’t have to be a scorcher for a runner to feel scorched.

Tons of other variables can cause an offset between physiological exertion and pace/speed. Hydration, fueling, stress, quality of the current podcast you are listening to—all can make an easy run harder than it should be. So, when in doubt, slow down. Your ego might be bruised, but your body will be happy.

—David Roche partners with runners of all abilities through his coaching service, Some Work, All Play

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