Regular interval exercise not only helps you lose weight (and keep it off for the long haul), it also strengthens your heart. Dr. Arthur Agatston, author of the bestselling The South Beach Diet Supercharged, recommends 20 minutes of interval exercise — which means alternating short bursts of intense activity (15 to 60 seconds each) with easier recovery periods — every other day. You can increase the length of time as you get fitter, but it’s not necessary.

Doing interval walking outdoors, or on a treadmill, elliptical machine, or stationary bike indoors, is a great way to get started. But intervals can also be done while swimming or riding a regular bike. (Note: On days when you’re not doing intervals, do core-strengthening exercises so that you’re working in some form of exercise every day.)

Whether you’re doing intervals outdoors or in, it’s important to change up your pace. Go at an Easy Pace for warmup and cool down (or if you’re just beginning an exercise program) and work up to Supercharged as you get fitter (see the pace explanations below). Just be sure not to do the entire workout at the fastest pace or you are more likely to suffer an overuse injury.

As your fitness improves, adjust your speed and/or incline (try some hills if you’re walking or biking outdoors), and resistance (on a machine) to match your new level of ability. Overall, speed is better than resistance. Increase resistance only to add intensity when you have achieved all that you can at maximum speed.

Here’s what the various paces feel like:

Easy Pace: When you’re working at a low level of intensity, you’re constantly moving, but you can easily carry on a conversation with a friend. This is the pace at which you should warmup before beginning the actual intervals and also the one you should use for a cool down when you're done.

Moderate Pace: When you’re exercising at a moderate level of intensity, you’re working at a brisk pace. You are breathing faster and can still carry on a conversation — but doing so is more difficult than at an easy pace.

Revved Up: When you’re revved up, you’re really moving! You’re a bit short of breath, and it’s hard — but not impossible — to maintain your pace. You should have difficulty carrying on a conversation at this level of intensity.

Supercharged: When you’re exercising at top speed, whether it’s walking or some other form of interval exercise, you are truly supercharged! You won’t be able to sustain the pace for long, but as you get fitter, the pace that once tired you out will become relatively easy and even your supercharged pace will get faster.

A Word of Caution: Talk to your doctor before you make a sudden change in your level of activity, especially if you are age 50 or older, have been inactive, have difficulty keeping your balance, have periods of dizziness, or have known heart problems.

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