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Volume 5, No 8 Information Technology News of the University of California, Davis Summer 1997

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Sports Mechanics Lab Helps Top Athletes

by Aviva Luria

What do throwing a javelin and driving a bobsled have in common? Some very important things, according to Mont Hubbard, Professor of Mechanical and Aeronautical Engineering. Like all sports, each involves motion, and motion can be described by the laws of mechanics. Both sports are among those that have been analyzed by Hubbard and his graduate students in the Sports Mechanics Laboratory here at UC Davis.

As director of the laboratory, Hubbard uses computer simulation and complex computation to help athletes improve performance. Hubbard accomplishes this by quantifying those aspects of a sport that are "optimizable," or that allow for improvement.

Optimizing the Flight of a Javelin

Take a look at the javelin throw. The athlete runs 20 to 30 meters before throwing the javelin, a motion that lasts approximately one-seventh of a second. The conditions on the javelin at the instant of its release determine how far it will travel.

Hubbard and his students have created a computer program that takes these quantifiable conditions and integrates them with equations of motion to determine the trajectory of the javelin. The program then creates a real-time graphical representation of the flight sequence. Using the system, a user can compare various factors--different javelins, changed conditions--that affect the distance the javelin travels.

Yet even if the thrower knows what conditions are optimal, the information may not be useful unless the athlete also has information about his or her actual performance. Another program developed by the lab measures athletic performance, making it possible to provide specific advice. Reflective tape is applied at equal points along the length of the javelin, and a high-speed video system automatically digitizes these points as the javelin travels through the air, quantifying the release conditions.

"If we can tell the thrower about the conditions of his or her throw, the athlete can compare these to the optimal conditions and change technique accordingly. It's a measurement tool that allows the athlete to hone in on the best set of release conditions," Hubbard says.

This analysis is especially important given the history of change in the sport. From the 1940s through the 1980s, the shape of the javelin had become so refined and so aerodynamic that it could actually generate enough lift to fly. Then, in 1986, after a javelin flew out of control and came close to hitting an Olympics official, the shape was again redesigned, making it more manageable, less erratic in its flight, and more resistant to traveling long distances.

Historically, world records have generally improved, Hubbard says, yet in 1986, after the redesign of the javelin, the 104.7 meter world record plummeted by about 15 meters. "The change had an immediate, abrupt effect on the world record, but now it's on its way up again," he says.

The Bobsled Simulator

Bobsledding presents its own challenges for engineers. Unlike a javelin throw, a bobsled run involves continuous motion. Although a bobsled's shape is very different from that of a javelin, and it travels on snow rather than through the air, the main difference is that the athlete controls its motion.

Hubbard and his students in the Sports Mechanics Lab have created a bobsled simulator that uses virtual reality to display the most effective way down a particular track. The simulator supplies data to four sensory systems that the driver would experience on an actual run: visual data (the view the driver has on the way down the track); vestibular (inner ear) sensations created by angular motions and accelerations of the head; tactile experience, or the "feel" of driving the bobsled; and auditory cues, similar to those the driver would hear on an actual course.

Solving equations of motion and incorporating the driver's steering into those equations one hundred times per second, the simulator draws a picture thirty times per second, thereby maintaining the driver's sense of visual reality. But most important, the program provides information to the driver that he or she wouldn't get in an actual run.

"We're computing everything," says Hubbard, "the forces on the sled and where the sled goes in response to the driver's steering. We can tell drivers where the sled went, and the difference in velocity from the fastest path down the track so far." Anything that is quantifiable, he says, can be shared with the driver.

"It would be extremely expensive to develop the instrumentation required to do this on the actual track, so the simulator has a lot of financial motivation behind it," Hubbard says. Bobsledding is an expensive sport, with tracks costing about $20 million to build, and sleds themselves costing anywhere from $25,000 to $40,000. For an athlete to practice on an actual track would require worldwide travel, and with runs on the track limited to four or five per day, the athlete's daily practice would amount to a mere five minutes for as many days as he or she could afford.

The site of the 2002 Winter Olympics, Salt Lake City has recently opened its new bobsled track. The UC Davis Sports Mechanics Lab, which already has installed a simulator at the U.S. Bobsled Federation in Lake Placid, New York, is currently building one to be housed in Utah, which Hubbard says may soon become the center for U.S. bobsledding. Hubbard is also attempting to obtain permission and data to program into the simulator the track at Nagano, Japan (site of the 1998 Winter Olympics). This summer, during a trip to Japan, he'll take photographs of the scenery surrounding the track in order to create for the simulator a realistic ambiance.

The Sports Mechanics Lab has received a good deal of media attention, including a spot on the PBS science program Nova. In fact, the lab's first donation of computers came as a result of a 1991 article in the San Jose Mercury News. The group had written the code for the simulator, but didn't have access to a machine that would run it fast enough to be useful. NASA and Silicon Graphics got involved, and loaned the group computers for their project. In 1994, IBM, an official Olympics sponsor, began its sponsorship of the lab with a loan of computers. The Lab now uses IBM RS 6000 high-speed graphics workstations, loaned by IBM for the project.

Initial and ongoing funding for the development of the simulator has come from U.S. Olympics Committee grants. The U.S. Bobsled and Skeleton Federation recently awarded the Lab with funding for continuing research and development.

In addition to its analysis of the javelin throw and bobsledding, the Sports Mechanics Laboratory researches baseball (both pitching and flight of the ball), fly casting, golf, and snowboarding. A recent project, in collaboration with the veterinary school, involves thoroughbred horses, and one graduate student is designing an amusement park ride for her master's thesis.