CU-Boulder researchers discover optimal range of slopes for extreme uphill running
Dec. 16, 2015
Rodger Kram
Racing on foot uphill on steep inclines is never easy, but researchers at CU-Boulder have
discovered a range of slope angles that actually erase the advantages of running versus
walking while ascending at a constant speed, says Rodger Kram, an associate professor in
the Department of Integrative Physiology and a co-author of the study.
CUT 1 “At these steep angles you can either walk or run because the speeds are pretty
slow. And we were curious as to whether it would be better to walk or to run. (:09) And
especially in this range of optimal angles walking uses less energy and it would be less
tiring than running at that same speed.” (:18)
The study is believed to be the first to examine the metabolic costs of human running and
walking on such steep inclines. The research focused on the challenges posed by vertical
kilometer races, or VK, which have grown in popularity in recent years in the U.S. and
Europe. Athletes must run or walk up steep slopes ranging between 10 degrees and 30
degrees in order to ascend 1,000 meters over a distance of less than 5 kilometers, or about
3.1 miles.
CUT 2 “We thought that there would be sort of a ‘Goldie Locks Angle,’ that is there
would be an angle where it was best and if you went any steeper then that would be
disadvantages. So we thought that there was going to be a single angle. And we though it
was going to be about 30 degrees based on these races that are done in Europe. The
records tend to be set on about 30 degrees. (:20) But what we found was there’s kind of a
broad plateau of angles - between about 20 degrees and 35 degrees - where it doesn’t
really matter.” (:29)
Researchers also recorded the athletes’ strides using high-speed cameras and found that
the mechanical differences between running and walking begin to disappear on extreme
slopes. Runners on flat ground experience an “aerial” phase during their stride when both
feet are off the ground but runners on steep inclines shorten their stride and make more
rapid steps while keeping one foot in contact with the ground at all times.
CUT 3 “Running involves an aerial phase where you’re flying through the air. You don’t
have any feet on the ground. But at these steep angles when we ask these people to run
they still had at least one foot on the ground. We used high-speed video and recorded the
rate that they took steps and from that we could calculate how long their steps were. (:17)
When people walked and ran at the same speed on these fairly steep angles they took
longer, slower strides when walking then when running. So that’s how we distinguished
walking and running by the rhythm of their steps.” (:30)
To conduct the study Kram says they had to build their own special treadmill – one that
would reach a 45-degree angle. But they found that angels steeper than 30 degrees
created special problems for runners and walkers.
CUT 4 “A typical gymnasium treadmill they only go to about 9 degrees of incline. We
made the world’s steepest treadmill, basically. We went to 45 degrees. We found that
people couldn’t balance when we had the treadmill inclined to 45 degrees. (:14) We also
found that people were slipping on the belt if we just used the belt as is. So we had to
take this grip tape from skateboards. It’s basically sandpaper with a sticky backing to it
and we attached that to the belt of the treadmill so that people had enough grip at 35,
almost 40 degrees.” (:30)
Kram says the next phase of the study will examine how trekking poles effect running
and walking uphill. He says they have become very popular with VK racers. The study
was recently published in the Journal of Applied Physiology.
For more information visit https://www.colorado.edu/news/features/cu-boulderresearchers-discover-optimal-range-slopes-extreme-uphill-running.
-CU-