There was a time in my youth when I thought I would never walk during a race. I gave up on this philosophy about two-thirds of the way to the mountain in Slovenia, where I competed in the 2010 World Mountain Racing Championships. The course climbed just over 4,000 feet in 7.5 miles. During a particularly steep stretch, I finally gave in and started walking. To my surprise, I didn’t lose ground in front of the runners around me. The lesson was learned, and I’ve been less dogmatic ever since.
I’m not alone though. According to Jackson Brill, a Salomon-sponsored runner and graduate student in the Roger Cram mobility lab at the University of Colorado, even among serious trail runners, there is sometimes a tendency to keep running at all costs. But when the hills get steep enough, walking becomes unavoidable, and deciding when to switch back and forth between the airs is one of the key tactical choices that track competitors must make. As it happens, Brill and his colleagues have been studying this problem for several years, and several recent studies offer some interesting new insights. Conclusion: “Our study,” says Brill tongue – in-cheek, ” gives people permission to walk if they want to.”
Yes, it works
To understand the transition between running and walking, you should start with a simpler question:is there a difference between them on steeper slopes? Under normal circumstances, one of the key differences between the two airs is that you always have at least one foot on the ground when you walk, while you leave the ground between each step when you run. But this rule of thumb breaks down into steep hills: even when you “run”, you never completely lose contact with the ground.
Not convinced? Take a look at this 2015 video from former Locomotion Lab researcher Wouter Hoogkamer working on the world’s steepest treadmill, which is ready to go up to 45 degrees (i.e. a 100 percent rating). I think he’s running, but he always has one foot on the ground.
Crum and his team blew up the same treadmill that was used for a slew of previous studies of running uphill, for a study published this summer in the European Journal of Applied Physiology. Led by first author Clarissa Whiting, a former Penn track star, the researchers recruited ten elite runners and had them run or walk on flat terrain and with a treadmill set at 30 degrees. That’s cool: Typical gym treadmills only go up to nine degrees, and black diamond ski runs tend to be around 30 degrees.
Of course, although runners always had one foot on the ground, there were clear differences between running uphill and walking. One track was a step pattern: on a slope, the pedal speed was 40 percent faster when running than when walking, and the feet stayed on the ground for 40 percent less time-a pattern similar, though less pronounced, to what you’d see on flat terrain.
But the smoking gun came from an accelerometer cut to the subjects ‘ waist, which measured the increase and fall of their center of mass. On flat terrain, walking produces two different acceleration peaks, one when you land and one when you tap. Running, by contrast, is a series of jumps from one leg to the other, producing only a peak of acceleration when you land and take off. Accelerometers found exactly the same patterns on the sloped treadmill, confirming that a steep uphill race really works, and not just some inflatable fast walk.
It’s intellectually interesting, but in practice you’ll almost certainly climb any 30-degree hill you encounter. So in a separate study currently under review (but available online as a preprint), Brill and Cram recruited ten other elite runners to run on zero, five, ten, and 15-degree slopes. The goal was to understand what motivates people to switch from running to walking or vice versa, and to determine whether our natural inclinations correspond to the most effective approach.
There has been a lot of research about walking and running on flat terrain. At slow speeds, we burn less energy when walking than when running; at fast speeds, it’s the opposite. Scientists used to assume that the decision to switch from walking to running was simply a matter of switching to the most efficient step. But a number of studies since the 1990s have shown that we actually tend to run at slightly slower speeds than expected when walking is more efficient.
There is no consensus on why this happens, but one theory is that some calf or ankle muscles get tired or have trouble building enough strength during brisk walking, so it’s more convenient to run, even if it costs a little extra energy. This makes intuitive sense-think about walking so fast that you decide to run. You change because it’s uncomfortable, not because you’re choking.
Brill and Crum found that this pattern persisted on slopes up to ten degrees: subjects switched from walking to running at a speed slower than the energetically optimal transition. But on the steepest 15-degree slope, the difference disappeared, and they started running just when it became more effective than walking. Once you climb a steep enough hill, it’s hard work, whether you’re walking or running, so it seems that the desire to conserve energy and be as efficient as possible takes over.
Crum notes that there is another, more subtle difference between flat terrain and steep climbs. There’s not much ambiguity on the floors about whether you should walk or run. At any given speed, one feels good and the other feels bad. In the mountains, on the other hand, there is a fairly wide range of conditions in which the solution is ambiguous. When you walk, you get the feeling that you will probably feel more comfortable. And this may be true for a short period of time after the change, but very soon you will have the feeling that walking might be more comfortable after all. There is no stable balance; you swing back and forth.
Another detail of Whiting’s research provides some possible insights about this. She attached electrodes to four different leg muscles in her subjects to compare muscle activation under different testing conditions. The sole, one of the two main calf muscles, showed 36 percent less activity per step during a steep uphill run than during a steep uphill hike, consistent with the idea that local muscle fatigue causes the transition. You walk until your feet-and perhaps the calves in particular-feel too uncomfortable. Then you start running, which initially feels better, but eventually leaves you more breathless, so you go back to walking and the cycle repeats.
For a competitive runner like Brill, it would be a good idea to put away some practical ideas about when to switch. In his study, he also tested heart rate as a proxy to figure out the most effective transition point. While heart rate values correlated with energy consumption, there were too many individual variations to make it useful in the real world. Brill’s next study, when the pandemic, fire, and other disruptions allow, will involve runners walking, running, or choosing their own combination of the two as they climb a real mountain. The goal, after all, is to be as fast as possible, not as efficient as possible.
For now, Brill will stick to the approach he discovered through trial and error, relying on his intuition about which ride feels best at any given time. Try not to switch back and forth too often, sticking to each gear for at least 15-30 seconds. He doesn’t consult a heart rate monitor. “It’s great that we did all this research,” he says. “But when I got to the road, I threw it out of the window.”
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