Hit a workout wall? Maybe you should consider a body double. Exercising with a buddy can have a tonic effect on your routine.

"Having a workout partner combines camaraderie with accountability," says Jeanette Modrick, a Colorado sports psychologist. "Plus, healthy competition can be a real motivator." An Indiana University study on couples who exercised together showed that they were seven times as likely to stick with their fitness programs as subjects who were partnerless. Want to double up? "The optimal buddy is someone with similar goals, someone who can coax you out of bed when it's pouring, but who also understands when you need a rest," Modrick suggests.In other words, don't pick someone who always whups your tail on the hills or spends the hour complaining: You'll only get frustrated and give up. Here's how to find your doubles match.

CHECKMATE: To land your ideal training pal, head to your local Road Runner's club (find it at www.rrca.org) or check out www.primusweb.com/fitnesspartner to peruse buddy personal ads.

DYNAMIC DUO: Play "follow the leader," switching off who sets the pace and who follows. Stay motivated and alternate who plans the workout agenda every day.