Trail runners on rocky terrain
Trail running research has taken off, matching the growing popularity of the sport itself. (Photo: Paedii Luchs/Stocksy)
Sweat Science

The Ultimate Guide to Uphill Trail Running

Here’s what the science says about making it to the top as quickly and efficiently as possible

Trail runners on rocky terrain

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At an endurance research conference in England back in 2015, I saw a surprising talk by a guy named Guillaume Millet. Longer races sometimes produce less muscle fatigue, he said. Running inefficiently can be an advantage in some contexts. Sometimes you should walk.

The context he was describing was mountain-ultra-trail races like the Ultra-Trail du Mont-Blanc and the even more daunting Tor des Géants, which covers 200 miles while climbing (and descending) three times the height of Mount Everest. Millet’s interest was not purely theoretical: he had placed as high as third at Tor des Géants, stumbling to the finish after sleeping less than three hours over the course of an 87-hour race.

Since that conference, trail running research has taken off, matching the growing popularity of the sport itself. Millet, who is currently a professor of exercise physiology at Université Jean Monnet Saint-Étienne in France, remains one of the leaders in the field, and he recently organized a pair of free webinars bringing together some of the top researchers and coaches in the field to discuss the state of the art in running up and down hills. Both sessions are worth watching (available on YouTube here for the uphill webinar and here for the downhill one). To whet your appetite, here are five key takeaways on running uphill.

Walk More

The first talk, from longtime University of Colorado biomechanist Rodger Kram, delved into the nuances of the walk-run transition. When, if ever, is it better to walk than run up a steep hill? It’s not a simple question, because the answer depends on factors like how steep the hill is, how fast you’re going, how aerobically fit you are, how strong your legs are, how long you have to continue, how technical the terrain is… and even how much peer pressure you’re feeling. “A lot of runners look down their nose at walking,” Kram pointed out. “I’m a runner, not a walker!”

On flat ground, it’s most efficient to walk at slower speeds and run at faster speeds. This is intuitively obvious, and you’ll automatically switch from walking to running as the pace increases. But intuition isn’t perfect for most of us: we’ll stick to walking for a little longer than we should, even at paces where running would be more efficient.

Heading uphill forces you to slow down and alters the ideal run-walk transition. For most people, walking is more efficient than running at slopes greater than about 15 degrees (equivalent to a 27 percent grade). For elite runners, running might still be more efficient at somewhat steeper slopes, but eventually everyone reaches a point where walking is the most efficient option. Note that “efficient” and “fast” aren’t the same thing: if you’re just climbing a short hill, you might still choose to sprint up it even though walking would be more efficient. But if you’ve got a long race ahead of you, efficiency matters—and most mountain runners have had the demoralizing experience of grinding up a steep incline then noticing that the person beside them is climbing at roughly the same pace even though they’re walking.

In practice, trail runners tend to alternate between walking and running on steep or long uphills. Research from Kram and his colleagues offers some hints as to why. Walking uphill seems to produce local muscle fatigue in the legs, particularly in the calves. To relieve that discomfort, we switch to running, which is more exhausting (because it’s less efficient on steep hills). When that gets too tiring, we switch back to walking, and so on. As a broad generality, Kram’s research suggests that people tend to stick to running a little longer than they should, so don’t be too stubborn about refusing to walk.

Kram also proposed a homework assignment to get more insight into your own habits. Find a hill that climbs about two miles, and time-trial up it three times: once only walking, once only running, and once alternating in whatever way seems optimal to you. See which approach is fastest, and use a heart-rate monitor to determine which one made you work harder. You can also use the cadence function on a GPS watch to determine when you switched between running and walking in the third trial, and assess how that affected your speed and heart rate. (If you do this, get in touch with Kram: he’d intended to do this as a formal study before COVID intervened, and is interested in seeing people’s results.)

Master Trail Efficiency

The second speaker, Frederic Sabater Pastor, is a colleague and former student of Millet’s. His research focuses on the energy cost of trail running: how can you cover the most ground while burning the least energy? There’s plenty of research out there on running economy, but Pastor’s data suggests that measuring running economy on a treadmill or even on a smooth, flat road doesn’t tell you much about how efficiently someone runs on rough, hilly trails.

There are plenty of possible reasons for that difference. Running on trails uses different muscles, with slower but more forceful muscle contractions and longer ground contact time when you’re climbing hills. Muscle damage from hilly terrain will also alter your efficiency. At altitude, your breathing muscles demand more energy because you’re panting in the thin air. And to a far greater extent than on the roads, technical ability matters: foot placement, coordination, and split-second decision-making about which route to follow.

That last point suggests that running efficiently on technical trails is a skill that takes practice to master. Other ways of boosting your trail efficiency include keeping the weight of your gear to a minimum, and perhaps strength training—though the latter approach hasn’t been proven in the lab, Pastor noted.

There are still plenty of mysteries about trail efficiency. In relatively short trail races of around marathon distance, runners get less efficient as the race progresses. In longer races between about 100K and 100 miles, there doesn’t seem to be any change. In super-long races like the 200-mile Tor des Géants, they actually seem to get more efficient by the end of the race. How or why that happens remains to be determined, which suggests there’s still plenty to learn about optimizing efficiency.

Save Your Legs

All this talk about efficiency seems fairly straightforward: more efficiency is always better, right? But Pastor added a caveat. As Millet and two colleagues pointed out in a paper back in 2012, there may be a trade-off between saving energy and saving your legs. It was ultra and trail runners who first fueled the rise of big, uber-cushioned Hoka shoes: the extra weight reduced efficiency, but the extra cushioning reduced cumulative muscle damage on long mountain runs and made the trade-off worthwhile.

There are other places where trail runners may choose to sacrifice efficiency. Top trail runners tend to have big, muscular legs, especially compared to whippet-thin elite road and track racers. That extra muscle might better resist damage over long, hilly runs. They might take shorter-than-optimal steps to minimize pounding. And most sacrilegiously of all, they might even run with poles.

Pole Up Steep Hills

The webinar’s third speaker was Nicola Giovanelli, of the University of Udine in Italy. He and his colleagues recently built the steepest treadmill in the world, with an especially wide belt so that he could test subjects climbing with and without poles. There’s been plenty of previous research on the use of hiking poles, with sometimes confusing results. In general, Giovanelli said, studies have found that walking with poles on level ground takes about 20 to 25 percent more energy than walking without poles at the same pace.

But the picture changes as you start heading up steeper and steeper hills. By the time you get to a slope of 20 degrees, walking with poles burns marginally less energy and perceived effort is substantially lower. The disconnect between energy and effort is presumably because poles allow you to split a given level of energy expenditure between your arms and legs, so that neither are pushed beyond their limits.

If, instead of measuring efficiency, you simply let subjects race up a steep hill, they do better with poles. In a study published this year, Giovanelli found that pole climbing was 2.5 percent faster than pole-less climbing for a hill with an average slope of 19 degrees that took about 20 minutes to ascend. Only three of 15 subjects were faster without poles. One of those subjects had conspicuously bad poling technique. The other two were the fastest subjects in the study. It seems likely that poles help most at slow paces, so fitter runners might get away without poles on fairly steep hills. Eventually, though, if the hill is steep or long enough, poles probably help everyone (if you know how to use them).

A final note: Giovanelli has been comparing the force applied to the poles with the impact force as your feet hit the ground. As you’d expect, people apply more force to the poles as the hill gets steeper. And the more force they apply to their poles, the less force their feet feel—perhaps another example of spending extra energy to save your leg muscles.

Train Like You’ll Race

The last speaker was running coach Jason Koop, who offered his perspective on how to apply trail running research to your training. In uphill races, the biggest engine generally wins—but there are ways you can tune the engine for the specific demands of trail races, he said.

For example, Koop shared data from a 35K trail race that one of his athletes had competed in. Using the cadence function from the athlete’s GPS watch, he was able to identify when the athlete was running, walking, or standing still. Overall, they’d spent about 66 percent of the race time walking and 33 percent running. That’s an important data point, Koop said, and one that should be reflected in training for the next race. Walking and running are two different strides, requiring different muscles and movements. If you spend all your training time running, you won’t be optimally prepared for a race in which you’ll be mostly walking.

Similar considerations apply to terrain. Running uphill, downhill, or on level ground each have different demands; the same is true for walking. In a sense, each of these activities is a different sport, and your training should reflect which skills you expect to need most, especially as you approach your specific preparation for a target race.

And with that, you’re ready to tackle even the steepest climbs! For more details, check out the full webinar.

For more Sweat Science, join me on Twitter and Facebook, sign up for the email newsletter, and check out my book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.

Lead Photo: Paedii Luchs/Stocksy

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