Each of you can take turns lying back, contracting core muscles and stretching leg muscles at the same time. Next, take a turn on the exercise ball. Sit down and hold a medicine ball. Lower yourself back, contracting abdominal muscles. When you get to a comfortable position lying back, lift up and throw your partner the medicine ball. He can opt to squat with the ball as you raise yourself up, completing the crunch. Switch places, and you'll have a full-body workout in no time. There's lots and lots of fun to be had in the great outdoors, so take things outside if you're feeling a little cooped up. Great workouts to do together include kayaking, biking and just taking a walk together. Regardless of what activity you and your mate choose, you'll get closer when you share a common goal.