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Where there are moving parts, there is also mechanics. This is especially true of the human skeleton. And it is something that has long fascinated Joakim Holmberg, mechanical engineer and senior lecturer at the Division of Solid Mechanics at Linköping University.

“It stems from my interest in skiing, combined with mathematics. Being able to make calculations on force and movement can be quite useful,” says Joakim Holmberg.

Not only does he teach and do research. He also supervises doctoral students in the subject of biomechanics, including at the Swedish School of Sport and Health Sciences. He also has interdisciplinary contacts with researchers at the Faculty of Medicine at Linköping University.

“We’ve started a collaboration with researchers in orthopaedics and hip joint operations. It’s about preliminary studies of polymers, polyurethane, which is a type of plastic. And load distribution between screws in different directions.”

Measerments on skiers

During his own doctoral studies at the Faculty of Science and Engineering, Joakim Holmberg carried out experimental measurements on skiers. This was a collaboration with the Swedish Winter Sports Centre in Östersund (NVC).

“We measured the forces of the ski poles, and we measured the position of the hand in relation to the forearm in order to measure a skiing movement, and then we measured various external forces,” he says.

He then developed a simulation model and calculated the power of different muscles and in total muscle work. Finally, he developed a measure of efficiency.

“I calculated it based on different skiing styles. An older style, roughly like the one used by ski legend Thomas Wassberg. And then one that many people use now. Wassberg’s style was more efficient. This style is still used for long distances, while the newer style is better suited for shorter ski races.”

Sit-ski

Other researchers have later come up with similar results. But Joakim Holmberg did not continue to study skiing styles. Instead, he supervises doctoral students and is co-author of various studies. One example is a study from 2022 by a doctoral student at the Winter Sports Centre in Östersund that deals with new solutions in para skiing, for people with disabilities.

“It’s about sit-ski, that is, where you sit on a kind of sled. Skiers are strapped to it and the study included calculations for an alternative way of sitting in the sit-ski,” says Joakim Holmberg.

With the traditional sled, the skier sits strapped with his legs folded up to his chest in a forward-leaning position. In the study, a new sled was tested where the skier has a more upright position and a support, i.e. a plate to lean forward on. This means less strain in the lower back but higher load in the shoulders.

“With the help of simulation technology in biomechanics, you can prevent problems that can be difficult to see in other ways. If you have no sensation in the area, you don’t get the same warning signals from your body.”

According to the study, efficiency decreases slightly with the new method.

“But it can be safer for the skier. They have no sensation in the disks in the lower back and don’t notice the load. This can be important knowledge as the sport develops.”

Alpine skiers

Joakim Holmberg also assists a doctoral student who works with simulation methods to find out when alpine skiers can start training after an injury.

“In alpine skiing this is hard to know. You may be feeling well, but still be a little weak in your sides, your knee or your muscles. This can make you more prone to another injury.”

By documenting different jumping exercises before the injury has occurred, it is easier to get back to the athlete’s movements after an injury.
“This study will develop more sport-specific exercises to get a more accurate idea of when you can start training and competing again,” says Joakim Holmberg.