CHAPEL HILL -- Thoroughbred horse racing, one of the top spectator sports in the United States, also is extremely dangerous, a University of North Carolina at Chapel Hill study confirms.

Jockeys weighing a little over 100 pounds steer high-strung horses weighing half a ton around dirt or grass tracks at close to 40 miles per hour. While racing, riders' heads bob up and down more than seven feet from the ground. With their bodies hunched forward over the charging animals' withers, any sudden change in speed or direction can turn riders into headfirst human missiles.

"Over a four-year period from 1993 to 1996, we found 6,545 injuries serious enough for treatment among about 2,700 licensed jockeys at 114 racetracks in the United States, " said Dr. Anna E. Waller, research assistant professor of emergency medicine at the UNC-CH School of Medicine. "We believe efforts need to be made to improve protective equipment and reduce the number and severity of injuries."

At least three jockeys were killed during the four years studied, Waller said. She and colleagues could not determine how many were permanently crippled and forced to retire.

Besides Waller, authors are Dr. Julie L. Daniels, postdoctoral fellow in epidemiology, Nancy L. Weaver, a doctoral student in health behavior and health education, both at the UNC-CH School of Public Health, and Dr. Pamela Robinson, retired professor of exercise and sport science.

The idea for the study came from Robinson, who raises thoroughbred horses in Kentucky. Her contacts with the Jockeys' Guild enabled the group to obtain and analyze insurance data from all U.S. professional thoroughbred racetracks. The single previous study of U.S. jockey injuries was a survey, which not all jockeys completed and returned.

Researchers found 606 injuries per 1,000 jockey years. Nearly one in five was to the riders' head or neck. More than 15 percent of injuries were to legs, more than 10 percent to feet or ankles, 11 percent to arms or hands and almost 10 percent to shoulders.

More than a third of mishaps (35 percent) occurred in or around starting gates. Those accidents resulted in almost 30 percent of the head injuries, almost 40 percent of the hand and arm injuries and more than 50 percent of leg and foot injuries. The home stretch and finish line also saw many accidents.

"Most head injuries resulted from being thrown from the horse or struck by the horse's head," Waller said. "Being thrown from the horse was the cause of 55 percent of back and 49.6 percent of chest injuries."

The study results likely are just the tip of the iceberg about jockey injuries since they did not have information about accidents that occurred on practice tracks and elsewhere, the researcher said. Companies have shown little interest in developing better protective equipment for U.S. jockeys since only about 2,700 such people ride professionally, and the potential market is so small.

By comparison, more than a million young athletes play football each year in this country. Among suggestions the UNC-CH researchers made for improving jockey and horse safety was to install padding, or more padding, inside starting gates and along rails. Work also needs to be done to improve helmets and other lightweight protective clothing, they said.

"Access to population-based data that weren't available before was a real boon," Waller said. "The Jockeys' Guild was excellent to work with and helped us every step of the way. There was a lot more information out there that we were not able to get from insurance companies, however, that would have been very useful. A lot more research can and should be done to boost jockey safety."

The National Center for Injury Prevention and Control supported the UNC-CH Injury Prevention Research Center project.