Circuit training is a fast-paced class in which you do one exercise for 30 seconds to 5 minutes and then move on to another exercise. It’s like a game of musical chairs: Everyone begins at a station (that is, a place where an exercise is done), and when the instructor yells “Time!” everyone moves to the next free station. Some classes alternate an aerobic activity (like stepping or stationary cycling) with a muscle-strengthening activity (like using weight machines). Others focus exclusively on muscle toning or aerobic exercise.
What circuit training does for you: Increases your strength and aerobic fitness and burns lots of calories. However, you don’t get the same level of conditioning as you would from doing your aerobics and strength training separately. If you take circuit classes, aim to get in an additional 20 minutes of straight aerobic exercise at least three days a week.