Off the Beaten Path

The Steeper the Better?

Any trail runner who has slogged up an unending series of switchbacks has wondered: wouldn’t it be easier to just charge straight up the hill? That’s the question at the heart of recent research by scientists at the University of Colorado in Boulder, who brought a group of 15 experienced mountain runners into their lab to run on a treadmill rigged to reach slopes of up to 45 degrees –far steeper than the 9 degrees a typical gym treadmill can reach, or the 25 degrees of a black diamond ski run.

The study was inspired by a punishing type of trail race called a “vertical kilometre,” where the goal is to run as fast as possible until you gain 1,000 metres of elevation. The men’s record of 29:42 was set on a course in Switzerland with an average slope of 27.5 degrees; the women’s record is 36:04. But is that slope really optimal?

There’s an obvious trade-off between very steep hills, where you gain elevation quickly but can’t maintain an efficient running stride, and very gentle rises, where you can run smoothly and easily but spend a lot of energy moving horizontally. The runners, who included former world junior mountain running champion Amanda Ortiz (a student at the university and also a member of the research team), ran at various slopes up to 39.2 degrees, which was the steepest they could manage without falling off. The treadmill was set so that they were gaining elevation at the same hard but sustainable rate – 0.35 metres per second – no matter what slope the belt was set at.

The results, which were published in the Journal of Applied Physiology, revealed a sweet spot between 20 and 35 degrees, where energy expenditure was minimized for the selected rate of vertical ascent. At 27.5 degrees, the Swiss vertical kilometre course is smack in the middle of this range, as you might expect.

Still, the study offered some unexpected insights. At slopes of 15 degrees or steeper, walking was actually more efficient than running, consuming less energy. Despite this, the subjects all reported that they preferred alternating between walking and running rather than sticking to the more efficient stride. Such preferences may ref lect the body’s innate ability to sense the most efficient movement pattern, says lead researcher Dr. Rodger Kram, so they’re worth paying attention to. In this case, the benefits of switching may come from using different sets of muscles when you alternate between walking and running.

So what do these results tell us? In situations where you have the freedom to choose your route up a hill, the optimal slope for rapid but sustainable climbing seems to be around 27.5 degrees, which corresponds to a grade of about 50 per cent: climb one metre for every two metres you go forward. And when you’re sticking to a trail, there’s no shame in walking when the route hits black diamond steepness. Sometimes that’s the smart (and efficient) thing to do.

“The study offered some unexpected insights. At slopes of 15 degrees or steeper, walking was actually more efficient than running, consuming less energy.”