Tennis "shoulder" from tough serves.

• Position: Sports Medicine

Anew 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 the Annals of Biomedical Engineering, could aid in sports training and rehabilitation, relates Allison Sheets, a former postdoctoral researcher in mechanical engineering at Stanford (Calif.) University, who now is on staff at Ohio State University, Columbus. With further development, 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 the body. 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 him or her as the individual moves. 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, along with her colleagues, is working to do away with the markers and take motion capture out of the laboratory. At Stanford, she was part of a team that designed a system of eight video cameras that record a person's movement 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.

A tennis serve is analogous to a baseball pitch, in that a player must

deliver the ball to a particular location. In baseball, it is the strike zone, and in tennis, it is the service box, an inbounds section on the opposite side of the court. 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...