Depending on your definition of "sport," you could be spending your time doing something highly active (tennis, anyone?) or something that's barely a step up off the couch (we're looking at you, bowlers). So what are really the "healthiest" sports? We set out to find which recreational activities give the best bang for your buck: burning calories, building strength and stamina and generally improving athletic performance. If you're looking for a way to make your next workout not feel so much like work, then try out one of these heart-pumping activities instead.