For those who prefer not to run due to injured knees, both swimming and biking are great cardio alternatives. Hopping in a pool or on a bike also helps to switch up your routine, so you end up working different muscle groups, which inevitably makes your entire body stronger and helps to prevent injury. How do biking and swimming compare though? Take this quiz to find out. You may have to reach back to your high school math class days to answer some of these.