That made me wonder, Where did this rule come from?

Carl Foster, director of the Human Performance Laboratory at the University of Wisconsin in La Crosse, said its origin “is lost in history,” and added, “Whether it is right is undocumented.”

It might be more correct to say “almost undocumented.” There is at least one large and rigorous study of the 10 percent rule, the sort of study that is a rarity in exercise science. Conducted by Dr. Ida Buist, Dr. Steef W. Bredeweg, Dr. Ron L. Diercks and their colleagues at the University of Groningen in the Netherlands, it’s one of a continuing series of studies on how to prevent running injuries.

The injury problem is huge, said Dr. Diercks, head of the sports medicine program at the university — as many as 40 percent of runners are injured, usually to their feet, ankles, knees or legs. At his university’s running clinics, 30 to 40 percent of beginning runners gave up because of injuries.

Although there are many training programs for beginning runners, none are based on good scientific evidence, Dr. Diercks said. He and his colleagues decided to conduct such a study.

Newsletter Sign Up Continue reading the main story Please verify you're not a robot by clicking the box. Invalid email address. Please re-enter. You must select a newsletter to subscribe to. Sign Up You will receive emails containing news content , updates and promotions from The New York Times. You may opt-out at any time. You agree to receive occasional updates and special offers for The New York Times's products and services. Thank you for subscribing. An error has occurred. Please try again later. View all New York Times newsletters.

They investigated the 10 percent rule because it is so popular and seemed to make sense with its gradual increase in effort. The study involved 532 novice runners whose average age was 40 and who wanted to train for a four-mile race held every year in the small town of Groningen.

Half the participants were assigned to a training program that increased their running time by 10 percent a week over 11 weeks, ending at 90 minutes a week. The others had an eight-week program that ended at 95 minutes a week. Everyone warmed up before each run by walking for five minutes. And everyone ran just three days a week.

And the results? The two groups had the same injury rate — about 1 in 5 runners.

Maybe, the investigators thought, they might prevent injuries with a conditioning program before the training started. So they did another clinical trial, randomly assigning one group of novice runners to a four-week program of walking, hopping and jumping rope before starting the running program. The others started right in with running.

The conditioning program had no effect. Once again, about 1 in 5 runners in both groups wound up with injuries.

Advertisement Continue reading the main story

The researchers are at a loss. Most people who take up running, Dr. Diercks says, think it will be easy — all they need is a pair of shoes. But in fact, running is a difficult sport, and most people quit before it becomes fun, often because they are injured. Experienced runners know how to adjust and return to the sport. Novices usually do not, he says.

Now the Groningen group wants to do a large and rigorous study of barefoot running, comparing it to running with shoes — another study that has never been done.

For now, though, the lesson is that running lore often is just that. And the 10 percent rule is a case in point.

“Nobody found out if it works or what is the basis of it,” Dr. Diercks said.

And that is the way it often goes in exercise science. People “hear something, they read something,” he said, “and then it’s like a religion.”