My friend Martin Strauss of Ann Arbor, Mich., was running 60 miles a week when he suffered a stress fracture that put him on crutches for three months. Now that he’s better, he wants to play it safe to avoid another injury. But what’s the best way to do that? How quickly can he ramp up the miles?

Martin decided to follow the 10 percent rule, one of the most widely known in running. It does not specify a starting distance but says you should increase your mileage no more than 10 percent a week. The idea is that this is a safe way to increase your distance without risking injury.

(Within limits, of course; if you started at 30 minutes a day and kept increasing 10 percent a week, after 41 weeks you’d be running 24 hours a day.)

Martin’s first run was on March 15. He ran half a mile, on a treadmill. Over the next five weeks, he increased his distance to ten miles a week, then began using the ten percent rule. Last week he ran 22 miles, including a long run of 10 miles. He calculates that it will take him a total of 18 weeks from when he started his program to get back to running 60 miles a week.