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Human modelling starts with the Achilles tendon

Human modelling starts with the Achilles tendon

21 Jun 2018

Computer modelling and simulation are familiar tools in the analysis of mechanical structures. Perhaps more surprising is that the same tools can also be used to model the human musculoskeletal system.

In his research, Academy Research Fellow Marko Matikainen from Lappeenranta University of Technology aims to determine by computation how a dynamic load affects soft tissues and vice versa.

A tendon is more than just a spring

Tendons, especially the Achilles tendon as the largest tendon in the human body, have a significant effect on human movement. The computational computer model to be developed could be used to examine how dynamic movement and changes in tendon parameters affect human dynamics.

However, according to Matikainen, the research so far is mostly equations at an elementary level. There are many challenges with, for example, tendon modelling.

“The material is rather complex. When a person moves, the performance causes transformations in the tendon, the positions of fibres change and energy is stored in the tendon. In the simplest of terms, a tendon can be described computationally using a spring-absorber combination, but this doesn’t allow the examination of changes at the fibre level in water-containing, porous material.”

Mechanical engineering gave way to biomechanics

Matikainen is not trained in the fields of medicine or bioscience. His background is in mechanical engineering, and even when preparing his doctoral thesis on computational mechanics, he could not imagine that he would end up researching anything related to the human body.

According to Matikainen, however, the combination is not in any way unusual – there are many experts of precisely computational mechanics working in the field of biotechnology.

“I became interested in the subject when I was an exchange researcher for the first time at Lund University. I’d been doing things related to mechanics for a long time and noted that it was a good time to expand my expertise.”

International cooperation is a prerequisite for research

Matikainen’s current funding period by the Academy of Finland will last until the end of 2021, and the additional funding it includes also allows taking on one full-time postgraduate student. The first year of postgraduate studies of Shiva Adika from India has been spent focusing on the development of a tendon elemental model.

The work of a second postgraduate student supervised also touches upon the research. The studies of Xinxin Yu from China focus on computational modelling of contact.

John Bruzzo, who defended his doctoral thesis on computational modelling of skiing last winter, has also participated in the research. The guy comes from Venezuela to Finland and ends up modelling skiing!”, Matikainen laughs.

The internationality of the research is also reflected in active researcher exchange. Matikainen has visited Lund twice over the years, and last year he spent two months as a visiting researcher in Hannover, Germany.

Group photo at Lake Saimaa. Left to right: Dr John Bruzzo, researcher Shiva Adika, Marko Matikainen and researcher Xinxin Yu.

According to Matikainen, biomechanics is not worked on much in Finland, with even less done on the inclusion of a soft tissue computational model in the human biomechanical model.

“The development of such technologies is much more advanced in Hannover, for example. Cooperation allows for significantly more efficient computing.”

At Lund, in turn, practical laboratory measurements are performed on the functioning of tendons. Their results can be utilised by researchers focused on computational mechanics, such as Matikainen, in their own work.

From vocational school to Academy Research Fellow with the support of teachers

The path of Marko Matikainen to the world of academia has not been the most direct one possible. Instead of attending upper secondary school, the boy from rural Kiihtelysvaara made it to university through vocational school and technical college.

“There has always been someone urging me to continue moving forward. Already at vocational school, one of my teachers said to me, ‘what are you doing here, you should proceed to technical college’. At technical college, in turn, my closest teacher recommended going on to the university of technology. Finally, at university, a professor persuaded me to pursue postgraduate studies even though I hadn’t even dreamt about it originally.”

Matikainen hopes that everyone would encounter someone at the right time who would encourage you to continue moving forward. From his own experience, he knows how great an effect that can have on your self-esteem and life course.

“Nevertheless, I’ve been very interested in the mathematical description of physical phenomena since I was secondary school age. It seems like I finally got what I didn’t even dare to wish for.”

Chance favours the prepared mind

For the time being, mathematical modelling of the functioning of the entire human body is still a distant dream. Even the functioning of a single muscle with its power production and commands from the brain is such a complex entity that it cannot be simulated with current methods.

Progress must be made in small steps. According to Matikainen, the goal during the next four years is to model the functioning of the human Achilles tendon during some simple gym exercise, such as squatting and rising up. It would serve as a basis for more demanding simulations in the future.

As the work progresses, even the modelling methods may still change as any of them is found to not work in practice: “On the other hand, the method used doesn’t matter as long as a working model is achieved. Fortunately, it’s possible to experiment with even wacky things in computer computing if there’s enough computing power. It’s of course good to have a sense of what’s worth trying, but lucky breaks are also needed”, Matikainen says.

Text and photos: Anna Dannenberg

Last modified 21 Jun 2018
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