Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Markerless motion capture offers a new angle on tennis injuries

18.01.2012
A new approach to motion capture technology is offering fresh insights into tennis injuries – and orthopedic injuries in general.

Researchers studied three types of tennis serves, and identified one in particular, called a “kick” serve, which creates the highest potential for shoulder injury.

The results, published in a recent issue of Annals of Biomedical Engineering, could aid sports training and rehab, said Alison Sheets, assistant professor of mechanical engineering at Ohio State University.

With further development, she added, doctors could use her “markerless motion capture” technique to diagnose patients.

“The potential for markerless motion capture in medicine is vast and exciting, because it can quantify how a person moves without the need to attach electronic markers or other equipment to their body,” Sheets said. “People can move naturally, and in a natural setting outside of a laboratory.”

Traditional motion capture technology works by attaching markers to a subject’s skin or clothing and tracking them as the subject moves, she explained. The markers can emit an electronic signal or reflect light, and the associated wiring and other equipment can limit or otherwise influence people’s movement. Moreover, the tracking has to take place in a laboratory setting, where lighting and background are carefully controlled.

Sheets and her colleagues are working to do away with the markers and take motion capture out of the laboratory.

For a project at Stanford University – where Sheets was a postdoctoral researcher before coming to Ohio State – she was part of a team that designed a system of eight video cameras that record a person’s movements at the same time, each shooting from a different angle.

A computer program combines the images to identify the 3D volume and shape of the person in each video frame. By comparing this shape to precise body measurements of the person under study, researchers can pinpoint the parts of the body that engage for a particular action, such as serving a tennis ball.

Study coauthor Marc Safran, MD, an expert in shoulder surgery at Stanford, proposed the project in order to investigate why he’d seen an uptick in the number of tennis players with shoulder injuries. Safran’s own 2005 research had shown that tennis injury rates had risen to as high as 20 injuries per 1,000 hours played, with most injuries to the upper body.

“To understand the cause of these injuries, we wanted to study how players move in a real, game-like situation,” Sheets said.

They recruited seven members of the Stanford men’s varsity tennis team for the study. The serve is the most often performed stroke in the game, so researchers focused on gauging the effects of three common types of serves on the players’ back, arm, and shoulder joints.

A tennis serve is analogous to a baseball pitch, in that a player must deliver the ball to particular location. In baseball, it’s the “strike zone,” and in tennis it’s the “service box,” an in-bounds section of the opposite side of the court. And – just like a pitcher – a server artfully delivers the ball to make it harder to hit.

The first serve in the study, the “flat” serve, is a straight shot down the center of the court – similar to a pitcher’s fastball. The second, the “slice” serve, requires the player to brush the racquet against the ball sideways during the hit. That gives the ball a slight spin that makes it skid across the ground and take an unpredictable bounce – somewhat analogous to the unpredictable flight of baseball’s knuckle ball.

The last, the “kick” serve, requires the player to brush the ball upwards from underneath, giving it a lot of topspin. Just like a pitcher’s curve ball, the kick serve sends the ball sideways along a wide arc. Ideally, it drops into the opponent’s service box from high above, and produces an equally steep bounce.

Sheets draws one big difference between a tennis serve and a baseball pitch, however.

“In baseball, a pitcher uses the arm like a whip. The movement is sequential – shoulder, elbow, wrist. But in tennis, the shoulder and elbow move together toward the ball, followed by the elbow alone and then finally the wrist, so that the racquet is moving the fastest right before ball impact.”

“For the flat serve, the player puts almost of all of the energy into moving the racquet in the forward direction,” she continued. “But for the kick serve, the player is also trying to precisely time upwards and sideways racquet movements to generate that characteristic spin.”

The study examined the difference in body positioning for the three serves. Researchers measured the distance between the vertical center line of a player’s body and the hitting surface of the racquet when the player hit the ball. For the kick serve, players swung the racquet closer to the center -- about 21 cm (8 inches) and 16 cm (6 inches) closer than for the flat serve and slice serve, respectively. The players also extended the racquet farther behind them for the kick serve: 8 cm (3 inches) farther than for the flat serve.

Those measurements suggest that the kick serve generates larger forces on muscles crossing the shoulder joint than the other two serves, which could promote injury, Sheets said.

She’s now working with Ajit Chaudhari and Timothy Hewitt of OSU Sports Medicine, who study ACL injuries – a tearing of a ligament in the knee joint. She also has a new project with D. Michele Basso, professor of physical medicine and rehabilitation, to use the technique with animals in order to develop more effective spinal cord injury rehabilitation protocols.

Sheets envisions that tennis coaches could use motion capture analysis of their players – both to prevent injury and improve performance. She doesn’t think the kick serve itself is going to change anytime soon, though.

“I can see how motion capture might change training and rehab, but I don’t think it’ll change how the game is played,” she said. “In tennis as in all sports, you do whatever it takes to keep your opponent on their toes.”

Other coauthors on the tennis study include Geoffrey D. Abrams and Thomas P. Andriacchi of Stanford and Stefano Corazza of Mixamo Inc. in San Francisco. The research was funded by the BioMotion Laboratory at Stanford.

Contact: Alison Sheets, (614) 247-6367; Sheets.203@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Alison Sheets | EurekAlert!
Further information:
http://www.osu.edu

More articles from Health and Medicine:

nachricht Researchers find trigger that turns strep infections into flesh-eating disease
19.02.2019 | Houston Methodist

nachricht Loss of identity in immune cells explained
18.02.2019 | Technische Universität München

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Light from a roll – hybrid OLED creates innovative and functional luminous surfaces

Up to now, OLEDs have been used exclusively as a novel lighting technology for use in luminaires and lamps. However, flexible organic technology can offer much more: as an active lighting surface, it can be combined with a wide variety of materials, not just to modify but to revolutionize the functionality and design of countless existing products. To exemplify this, the Fraunhofer FEP together with the company EMDE development of light GmbH will be presenting hybrid flexible OLEDs integrated into textile designs within the EU-funded project PI-SCALE for the first time at LOPEC (March 19-21, 2019 in Munich, Germany) as examples of some of the many possible applications.

The Fraunhofer FEP, a provider of research and development services in the field of organic electronics, has long been involved in the development of...

Im Focus: Regensburg physicists watch electron transfer in a single molecule

For the first time, an international team of scientists based in Regensburg, Germany, has recorded the orbitals of single molecules in different charge states in a novel type of microscopy. The research findings are published under the title “Mapping orbital changes upon electron transfer with tunneling microscopy on insulators” in the prestigious journal “Nature”.

The building blocks of matter surrounding us are atoms and molecules. The properties of that matter, however, are often not set by these building blocks...

Im Focus: University of Konstanz gains new insights into the recent development of the human immune system

Scientists at the University of Konstanz identify fierce competition between the human immune system and bacterial pathogens

Cell biologists from the University of Konstanz shed light on a recent evolutionary process in the human immune system and publish their findings in the...

Im Focus: Transformation through Light

Laser physicists have taken snapshots of carbon molecules C₆₀ showing how they transform in intense infrared light

When carbon molecules C₆₀ are exposed to an intense infrared light, they change their ball-like structure to a more elongated version. This has now been...

Im Focus: Famous “sandpile model” shown to move like a traveling sand dune

Researchers at IST Austria find new property of important physical model. Results published in PNAS

The so-called Abelian sandpile model has been studied by scientists for more than 30 years to better understand a physical phenomenon called self-organized...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Global Legal Hackathon at HAW Hamburg

11.02.2019 | Event News

The world of quantum chemistry meets in Heidelberg

30.01.2019 | Event News

Our digital society in 2040

16.01.2019 | Event News

 
Latest News

A landscape of mammalian development

21.02.2019 | Life Sciences

Surprising findings on forest fires

21.02.2019 | Earth Sciences

Atopic dermatitis: elevated salt concentrations in affected skin

21.02.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>