Why Trainers Say, 'Slow Down' [news]

When his running coach implored him to take rest days, Bill Carr didn't listen. Slated to run a 100-mile ultramarathon this month, the 36-year-old cranked up his workouts over the summer, running more and harder miles than his coach recommended. Running coach Julie Fingar guides Bill Carr, who ran too much and injured his ankle, in drills at a Twin Rocks trail near Folsom Lake in Granite Bay, Calif. "I wanted to make sure that I got to the event fully prepared," he says. But Mr. Carr won't get to the 100-miler at all. Last month, his ankle sustained an over-use injury during a workout, sidelining the Rancho Cordova, Calif., project manager for a vision-benefits company. "Type A personalities will increase their training load until something backfires," says Julie Fingar, Mr. Carr's running coach, who says her biggest challenge is convincing her clients to take an adequate amount of rest. "In their minds, taking rest means they're not working hard enough."