Aerobic exercise not only helps you lose weight (and keep it off for the long haul), but it also strengthens your heart. Dr. Arthur Agatston, author of the bestselling South Beach Diet Supercharged and The South Beach Heart Health Revolution, recommends a minimum of 20 minutes of interval exercise — like walking (during which you’d alternate periods of fast walking with periods of slower recovery walking) — every other day.

No worries if you’d rather hit the gym (or work out in your home) than head outdoors. You can do your interval-training program on a treadmill, a stationary bike, or an elliptical machine, as well as at home or outside, by following the intensity levels described here.

(Note: On days when you’re not doing interval training, take a recreational walk for 15 to 20 minutes or do other core-strengthening exercises so that you’re participating in some form of exercise every day.)

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 will usually be doing your warm-up before beginning the actual intervals.

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.

Revved Up: When you’re Revved Up, you’re really moving! You’re a bit short of breath, and it’s difficult — 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 cycling, 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.

As your fitness improves, you should adjust your speed, resistance, and/or incline (if you’re using a machine) to match your new level of ability for each of the paces. Overall, speed is better than resistance. Increase resistance only to add intensity when you have achieved all that you can at maximal speed.

Treadmill

• Start at an Easy Pace and gradually increase your speed to Moderate Pace.
• When you reach Revved Up, adjust the incline so that you’re working at a higher resistance. At this point you are ready to begin doing your intervals.
• Tip: When selecting a higher resistance level, know that you can drop back into your slower recovery pace when you need to.

Stationary Bike

• Adjust the seat so that you’re comfortable. Each leg should be only slightly bent at the bottom of each pedal stroke.
• Start cycling slowly to warm up. Change your intensity by either cycling faster or increasing the resistance level. To work at the Revved Up or Supercharged level, you will have to increase both.
• Tip: You use your muscles differently on a bike than you do when walking, so allow your body to get used to the new movement pattern and be sure you’re maintaining your proper form.

Elliptical Machine (cross trainer)

• The workout for an elliptical machine is similar to that for a stationary bike or a treadmill, but the way you use your muscles differs.
• Once you’ve achieved your maximum speed, increase the intensity.
• Tip: Experiment with both the incline and resistance levels to see what combination is most effective for you.

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