After taking a pounding every week during the NFL season, Brent Celek, a tight end for the Philadelphia Eagles, goes into recovery mode. In the off-season, Mr. Celek swaps field drills and wind sprints for yoga and Pure Barre classes.

Heading into his eighth year in the league, Mr. Celek, 29, says during the season he puts in at least two hours a day on the field doing drills and one to two hours three days a week in the weight room. By January, his body is ready for a break. He took about three weeks off after the season...