Washington, Jan 18 : Using a new approach to motion capture technology, researchers have identified a tennis serve called a "kick" serve, which creates the highest potential for shoulder injury.

It is one of the three types of serves the researchers studied using the new approach that offers fresh insights into tennis injuries - and orthopedic injuries in general.

The results 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.

Traditional motion capture technology works by attaching markers to a subject's skin or clothing and tracking them as the subject moves, Sheets 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.

"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. People can move naturally, and in a natural setting outside of a laboratory," Sheets said

"To understand the cause of these injuries, we wanted to study how players move in a real, game-like situation," she stated.

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.

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.

The study published in a recent issue of Annals of Biomedical Engineering. (ANI)