Alpine skiers can reduce their aerodynamic drag by making slight tweaks to the angle of their hips and torso in a tucked position, according to new findings that were derived from elite athletes and add to the scant body of research on the physics of downhill skiing, a closely guarded trade secret.
In an article published March 1 in the Journal of Biomechanics, Norwegian researchers also revealed that a skier's legs generate a surprising amount of the aerodynamic drag compared to the rest of the body, at 40% to 50% of the total.
Skiing is important in Norway, which opened its first indoor skiing center last year, as suitably snowy slopes become rarer with climate change. This study, by researchers from the Norwegian Institute of Science and Technology and the University of Stavenger in Norway, with backing from the Norwegian Olympic Committee, aimed to help make Norwegian skiers faster — and to earn more medals at the 2022 Winter Olympics in Beijing — but to also fill a gap in scientific literature.
"I think many teams do internal measurements, but they don't want to share the results, so if you look into alpine skiing there's not much coverage," lead author Ola Elfmark, a Ph.D. candidate at the Norwegian Institute of Science and Technology, told The Academic Times. "We wanted to look into the main structure, how you have your knees and how you have your thighs, upwards, downwards, or close together — that's the most basic thing that decides drag."
The researchers conducted wind tunnel experiments with professional alpine skiers to determine where the most drag occurred on each skier, and how it changed depending on the angle of their thighs and torso.
After a couple of long days subjecting two skiers to winds between 90 and 126 kilometers per hour, and replicating their findings in a computer simulation, the researchers found that a tuck position where the angle of a skier's torso approaches 0 degrees against the wind, and closes the space between their arms and knees, effectively mitigates drag.
Conversely, in tests of other positions, drag increased by about 1% per degree, as the angle of each skier's knees and torso rose above their baseline tuck position.
Alpine skiing has always been a battle against drag, which accounts for 80% to 90% of the force reducing a skier's speed. So the tuck position itself is not new; it is the low, crouched pose skiers have always assumed when they need to accelerate down the slopes. Aside from body position, the fabric of a skier's outfit also determines aerodynamic drag.
But neither scientists nor skiers knew how the tuck worked in aerodynamic terms, or what could be done to optimize it, aside from the simple fact that a smaller surface area means less drag.
Even though this research could improve results for some skiers, it would be impossible to complete a race entirely in the tuck position. Skiers need to be loose and adapt to the contours of each slope, and often must raise their head to see what's coming ahead.
"You can go say to the athletes, 'OK, if you are able to reduce your torso angle by 5 degrees you will go 0.1 seconds faster on this track,'" Elfmark said. "But sometimes they don't have the opportunity to choose their position, because on some hills or terrains they have to increase their thigh angle. But if they can choose, it is important to know which is the best."
While aerodynamic research in sport is usually shrouded in competitive secrecy, Elfmark is happy to contribute to a greater global understanding of the physics behind alpine skiing. He plans to continue this research, and share it, by examining how arms affect drag, while leaning more on computer simulations rather than live skiers.
"In sports, the general attitude when it comes to aerodynamics is to not publish results, because [teams] think, 'OK, now our competitors are getting our results and that's bad,'" Elfmark said. "But I think this is the way to move the sport forward."
A relatively small country of just over 5 million people, Norway regularly performs well in alpine skiing competitions, taking home seven medals at the 2018 Winter Olympics in Pyeongchang. Despite sharing his findings with rivals, Elfmark is confident in his country's skiing prowess, and the research that backs it.
"Publishing a paper takes a lot of time, so even if the Swedes or the Americans get hold of this, we are already many steps further in our process," said Elfmark. "If this is new to them, then they are really far behind."
The study, "Aerodynamic investigation of tucked positions in alpine skiing," published March 1 in the Journal of Biomechanics, was authored by Ola Elfmark, Norwegian University of Science and Technology; Knut Erik Teigen Giljarhus, University of Stavanger; Fredrik Fang Liland and Luca Oggiano, Nabla Flow; and Robert Reid, Norwegian Ski Federation.
Correction: An earlier version of this story referred to Ola Elfmark as a coauthor of the study. He is in fact the lead author. This has been corrected.