When a dumbbell gets lifted, it doesn't go anywhere or do anything. It hovers for a moment, and returns to where it was lifted from. While good exercise, where's the play? Otherwise known as workout fatigue, what plagues gym-goers can be remedied in recreational sports. Things like roller-skating and ping pong simultaneously burn away calories while providing a more stimulating experience, something lost in an "on-rail" gym experience. Read on for 8 examples and their surprising health benefits.