You don't have to go it alone. In fact, some experts say you'll actually burn more with a buddy.

Madonna and Gwyneth hit the gym together. Lance Armstrong and the ever-shirtless Matthew McConaughey go biking, rock climbing, and running in tandem. And it looks like these celebs are on to something. "Pairing up with a workout buddy can dramatically improve your overall results," says Mel Joyner, a New York City-based personal trainer who works out with a buddy 95% of the time. Here, a quick look at why doubling up is worth your while:

You'll get out of bed. If you know someone is meeting you at the gym in the morning, are you really going to slap the snooze button and sleep in? Unlikely. "When you schedule workouts with a friend, you're held accountable, so you're less likely to skip out on a workout," says Joyner.

You'll make it a habit. People are used to moving from appointment to appointment during the workday, so meeting a workout partner at the gym will just feel like another appointment in a busy day. "I believe strongly that you should make a point of going to the gym with a friend during the first few months of your gym membership," says Dr. Belisa Vranich, a clinical psychologist and member of Gold's Gym's Fitness Institute. Why? "Working out should be a habit, and it takes 21 days to form a habit. If you're going it solo, you're likely to slack off during those three important introductory weeks, but if you're regularly meeting a friend, the habit is more likely to set in."

You'll work harder. "When I work out on my own, I'm not likely to force myself to do extra reps or increase my speed on the treadmill," says Joyner. "But if I'm working out with a friend — ideally a friend who is stronger and faster than me — you can bet I'll try to one-up the other person by doing more chin-ups or running faster in a race or lifting more weight on the machine." Adds Vranich: "A good friend can read your facial cues and body language, so he'll know when you're slacking off and, as a result, give you that extra nudge or a few needed words of encouragement."

You'll diversify your workout. "There are a variety of workout moves that you can only do with a partner," says Joyner. His favorite? The wheelbarrow push-up, where one person does a push-up while the other (standing) person holds on to the ankles. "The holder has to squat as the person goes down toward the floor, so the exercise works the muscles of both involved."

You'll stay social — without loading up on calories from food and drink. Let's face it: working out alone can take time away from your social life. But working out with a friend allows the two of you to catch up on work, life, and all the rest without doing so over, say, five frosty — and calorie-laden — beers. You're killing two birds (and, quite possibly, two beer guts) with one stone. Joyner learned this important lesson in college. "After my friends and I bonded over one two many boxes of pizza, we decided to center our social activity around the weight room as opposed to the pizza joint," he says.

Convinced? So how do you find a workout buddy if you don't already have one? Joyner, for one, has found a number of workout partners in public parks. "I'll be doing pull-ups and dips and, before I know it, several people will have joined me on the bar or bench and the conversation just goes from there. Suddenly, we'll make arrangements to meet up the next Saturday at the same time." He's also met plenty of partners at the gym. "Your best workout partner could be the person next to you during that grueling kickboxing class," says Joyner. "Don't be afraid to strike up a conversation — after all, you're at the gym for the same reason: to look and feel better."