Alan Barr raced down the track at Tucker High School near Richmond, chest heaving, mouth open to suck in air, arms pumping, legs digging into the wet, slippery surface on a cold Saturday morning earlier this month.

A visitor who rarely watches track events was impressed with the high school junior's speed.

After catching his breath, Barr ran again. This time, there were two differences: He ran even faster; it was like watching a speeded-up movie or video-tape. He was holding two small metal handles attached to a long cord. Barr was being forced to run faster, literally being reeled in toward a contraption mounted on a low post set into the ground at the other end of the track.

The recently patented device, called the Sprint Master, was invented by Barr's track coach, John Dolan, and Mike Watkins.

More than 50 high school and college track teams and football teams, and three professional football teams have shelled out $995 apiece for the Sprint Master, which uses a 5-horsepower gasoline engine to turn an aluminum spool that reels in up to 100 yards of rope at controlled speeds.

Dolan said that, when a runner is using the Sprint Master, stride length and frequency increase.

"Physiologically, we feel that running with the Sprint Master sets up new neurological patterns, teaches you to run faster" and upgrades muscle fiber, Dolan said.

Dolan said that one of his runners started with a speed of 13.8 seconds for the 100-meter race, but became the fastest sprinter on the team after two months of training with the Sprint Master, cutting his time down to 11.4 seconds.

"If it hadn't happened to me, I wouldn't have believed it," the coach said of his runner's improvement.

Every member of the Tucker track team gets "towed" -- as the Sprint Master sessions are called -- two or three times a week. Some runners become acclimated to towing in one day, while others take longer.

Monica Davis, a sophomore, is going to run the quarter-mile this season. Her best time for that event is 69 seconds. "I was fighting it the first time," she said of being towed by the Sprint Master.

Annette Brand, 16, a junior, also runs the quarter-mile. This is her third year on the team. Her best time for the event is 68 seconds.

"I never thought I could run that fast," she said. Being towed is "scary at first, but once you know you're not going to get hurt, you sort of just work on going faster."

According to Dolan, his invention is just an improvement on the original version of towing, in which coaches try to increase someone's running speed by having him or her run while holding a rope attached to the bumper of a moving car. They got the idea from Finnish runner Paavo Nurmi, whose training for his 1920s Olympics victories included running while holding onto slow-moving trains to force himself to run faster.

Dolan said that coaches long have been looking for a better way to tow runners because it is difficult to watch the road, the speedometer and the rear-mirror view of the runner simultaneously, because holding a tow bar prevents a runner from developing proper arm motions and because no one considers it healthy to run so close to an auto exhaust pipe.

Dolan wasn't the first person to realize the advantages of using a stationary mechanism to tow runners, but he was the first to figure out how. In 1975, he came up with the idea of an engine-powered pully anchored to a post; in 1981, he started sketching possible mechanisms; and in 1983 -- after 17 prototypes -- he made his first sale, to a high school in Fort Lauderdale.

Other customers have included the Chicago Bears, Cleveland Browns and Dallas Cowboys professional football teams, and the University of Maryland. Dolan said that he has talked with the Washington Redskins, but that Dan Riley, the team's strength coach, puts players through the Nautilus fitness system, leaving no time for Sprint Master use.

Dolan figures that he and Watkins -- a friend who solved many of the mechanical problems with the invention -- each put about $6,000 into the venture, and that they have to sell about 50 more Sprint Masters to break even.

Asked to assess Sprint Master's effect on runners and other athletes, Dolan said: "It's almost as if you can buy speed. You can make a guy stronger with weight-lifting . Well, you can make a guy faster" with Sprint Master . However, he said that there is no way to predict how much faster Sprint Master can make a given athlete. "There is no perfect form in running," says Dolan. "There is a general form that is efficient. The Sprint Master takes your quirks . . . and teaches you how to move those quirks as fast as you can.