TOTAL WORKOUT TIME: 20 minutes
When you need to squeeze in a quick workout or break out of a rut, consider circuit training. It gives you an efficient, calorie-burning, heart-pounding and muscle-strengthening workout in half the time..

Circuit training is effective because of the quick-hitting pace in which the exercises are done. Instead of completing an exercise and then resting for a minute, in circuit training you begin the next set immediately. You continue to go rapid-fire, until you’ve completed the entire circuit. You can then rest for 90 seconds, and repeat the circuit.

Even if you’re performing weight lifting moves in the circuit (starting with lighter weights than usual, given how tough it is to keep moving without rest), you’ll get a cardiovascular workout. The result: Not only will you burn fat and build muscle, but you’ll do it in about half the time.

The following 20-minute circuit workout can be done 2 to 3 times per week. After a brief, total-body warm-up, do all of the exercises in order for 12-15 repetitions per set, moving quickly to the next exercise. Once you’ve completed all six exercises, rest 60 to 90 seconds, and begin the second and final circuit.

As you become fitter, work up to doing three full circuits, and increase the intensity by foregoing the rest period between circuits and doing 2 to 3 minutes of moderate cardio exercise (such as riding a stationary bike or jogging briskly in place) instead.

Before you begin, warm up by jogging in place for a minute, then stretch (seated with knees slightly bent) by leaning forward to touch your toes, or by bending and straightening your knees several times. Stretch for a few minutes after your workout, too.