Cross training is the exercise strategy of doing a variety of workouts. For example, if running is your workout of choice, you can cross-train with biking, skating, swimming or other aerobic activity on the days between your running days.

There are lots of good reasons to cross train. It helps guard against overuse injuries that can result from doing only one type of workout. It can build different muscles (or different parts of muscles) than your primary activity does. And it enables you to get a good cardio workout on your days off from your primary workout.