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 Norovirus evades immune system by hiding out in rare gut cells
12.10.2017 | University of Pennsylvania School of Medicine

nachricht Flexible sensors can detect movement in GI tract
11.10.2017 | Massachusetts Institute of Technology

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Ocean atmosphere rife with microbes

17.10.2017 | Life Sciences

Neutrons observe vitamin B6-dependent enzyme activity useful for drug development

17.10.2017 | Life Sciences

NASA finds newly formed tropical storm lan over open waters

17.10.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>