1. You'll be more motivated.
Don't feel like working out after work? It's one thing to cancel plans with yourself but it's another to cancel on your friend—someone who's counting on you. "No one wants to be Debbie Downer by bailing and letting down your friend," says Steve Stonehouse, the Personal Training Manager at Crunch gym in New York City. You're much more likely to meet your friend for a planned workout session at 6 p.m. compared to tentative plans you made with yourself for, say, sometime after lunch. "After three or four weeks, once you're in the habit, you won't even think about canceling on your friend," adds Stonehouse.
2. Your workouts can be more fun.
News flash: The treadmill and the bench press aren't the most exciting ways to pass the time. With a partner, you can get your heart racing in more interesting ways (yes, we're still talking about the gym). Together, you can play one-on-one basketball, tennis and squash. "You can also take turns leading new exercises and switching up the routine," suggests Stonehouse. Maybe you know a brutal leg lunge that you used to do on your own? Teach it to your buddy one day, and the next, let him teach you something new. "Your body adapts and becomes efficient at moves that you've done again and again," says Stonehouse. "The more you change up your workout, the better your body is going to respond."
3. You'll work out harder.
"Whenever you're working out with someone else, the intensity is always going to be great than when you're alone," points out Stonehouse. (You don't want to be the weak one who can't keep up with a seven-minutes mile!) One key tip when picking your partner: Your athletic abilities should be in the same ballpark. A more seasoned gym-goer won't get as much out of working out with a newbie. "If you're on the same level, you can push each other," Stonehouse says. Odds are, you'll both want to quit around the same time but you'll go a little longer if your friend is still at it.
4. You'll finally be able to afford a personal trainer.
Sharing a cheeseburger is cheaper than buying one yourself. The same math applies when it comes to a personal trainer. At Crunch, where Stonehouse works, for example, a one-on-one session costs about $85. Yet a session with a partner is around $50 per person. "One-on-one training is still the bulk of my day but I'm seeing more and more partner training for financial reasons alone," says Stonehouse.
5. You'll always have a spotter.
Never again will you have to approach a random meathead and ask him to spot you. Never again will you have to count your own reps. "You also won't have to worry about forced reps," adds Stonehouse. What's a forced rep? "Let's say you're on the bench press and you want to stop at 10 because you're not sure you can make it to 11. If you have a spotter, you don't have to worry as much and you are more likely to power through the 11th, 12th and 13th reps. And each of those little lifts will add up and make a difference." Use your spotter to keep an eye on your form as you work, too.
6. Your friends will be thinner.
Before you judge us, we're not being totally shallow here—having thin friends is for your own good. Researchers at Harvard University found that you can "catch" obesity (along with smoking habits and happiness) because it spreads like an infectious disease. The experts found that a person's risk of becoming obese rises by two percent for every five obese social contacts they have. "There's definitely some truth to that," agrees Stonehouse. "If you're surrounded by people who are active and eat well, there's a good chance you're going to do the same."