Step aerobics classes are popular at health clubs and can be a social outlet for those who enjoy group exercise. As runners we tend to move in just one direction. A step aerobics class will have you moving in all sorts of different pattern and work muscles that may get neglected with running. There is a moderate amount of impact with these classes (this will vary with instructors), which may not make it the best choice for some injuries.
A study conducted at Auburn University reported that step aerobics resulted in similar improvements in the ability to use oxygen (VO2 Max) as running. The unique aspect of this study was that they compared injuries between the two groups. Step aerobic exercisers reported more injuries that caused pain only while bench stepping, whereas runners reported slightly more injuries that continued to hurt after running.