Using magnetic gates to track slalom skiers' performance

February 27, 2017 by Sandy Evangelista, Ecole Polytechnique Federale de Lausanne
Credit: Ecole Polytechnique Federale de Lausanne

EPFL researchers can now measure a slalom skier's exact time at each gate all the way down the slope. Their system also calculates the skiers' speed and trajectory more accurately than GPS.

Whether they're racing the slalom or giant slalom, skiers all face the same imperative: to round the as fast as possible. But when it comes to carefully analyzing their performance, existing technologies provide only limited information. This includes some split times along with video images – which have to be reviewed manually. Coaches have also tried GPS-based systems, which track the skiers' speed and trajectory, but they're not always that easy to use.

Benedikt Fasel and the team at the Laboratory of Movement Analysis and Measurement (LMAM) have now come up with a way to closely track performance on each section of the slalom course by drawing on several different technologies. "We found that by combining systems designed for different purposes, we could determine a skier's time, speed and trajectory both accurately and automatically."

They started with accelerometers and gyroscopes, which measure the skiers' acceleration and angular speed. This data is used to determine the orientation of different parts of the body, such as the hips, knees and torso. The researchers then added a magnetic system to measure the elapsed time at each gate.

The inertial sensors do not directly track the ' speed or position. These two pieces of information have to be calculated using measured accelerations. But these calculations are highly susceptible to errors, which can result, for example, from the vibration caused by either the skier's speed or movements. "An ordinary or low-end GPS, like the type used in mobile phones, can measure speed and position with a lower level of error. But these systems are not accurate enough. We'd like a resolution of 10 to 15 centimeters," said Fasel. That led to the idea of combining data from inertial sensors and magnets.

Magnetic gates

The researchers equipped every gate with a magnet and put a magnetometer on the skier. "The magnetic field is strongest when the skier rounds the gate. If we know the amplitude, we can also calculate the distance. Using this information, we can figure out how far the skier is from the gate and determine their speed." Since the exact position of the gates is known, errors in the acceleration-based speed and trajectory calculations can be corrected at every gate.

Credit: Ecole Polytechnique Federale de Lausanne

The researchers' method was successfully tested on 17 runs down a giant slalom course. A high- camera was used to verify the magnetometer readings. It showed that the skier rounded the gate at the exact moment that the amplitude was greatest. The EPFL lab has filed a patent for this technology.

"Our ultimate goal is to help athletes and coaches identify room for improvement on the basis of scientific data rather than intuition. The magnets let us map the skier's with precision. So we can analyze the line the skier takes and their strengths and weaknesses," added the researcher.

Credit: Ecole Polytechnique Federale de Lausanne

Explore further: The aerodynamics of speed skiing

Related Stories

The aerodynamics of speed skiing

March 6, 2013

( —By studying the aerodynamics of speed skiing, Engineering student Robert Sills is developing methods to improve results of the British Speed Ski Team by reducing aerodynamic drag.

Ski design inspired by turtle scales

April 4, 2016

These alpine skis change stiffness in response to the skier's position. EPFL researchers helped develop the new skis thanks to a mechanism that mimics turtle scales.

Signal opportunities on the slopes -- with RFID

March 3, 2009

( -- Whether slalom or alpine skiing, competitive skiing is all about thousandths of a second. Hence, professional athletes must constantly refine their technique. Small radio transmitters will make it possible ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.