1. Step on the gas. Alternate the speed and intensity of any activity you're doing. For instance, if you're walking, do a few minutes at a moderate pace, then speed-walk or jog for a few minutes; repeat. If you're running, go for a few minutes, then sprint for a minute and repeat. Do the same with cycling, inline skating, swimming or any activity of your choice.

2. Go for a bonus. Do an extra 15-20 minutes of cardio in addition to and apart from your regular aerobic workout. For example, if you usually go to the gym after work, wake up 20 minutes earlier and head outside for a brisk morning walk, hike or bike ride in your neighborhood; it'll be an energizing change of pace. (Just remember to warm up as always; high-intensity exercise early in the morning when your body temperature is still low can lead to injury.)

3. Add some muscle. Incorporate some strengthening and toning exercises into your walks or runs: Do shuffles, step-ups, high-knee jogs or other exercises (see # 5 below) at the end of every fourth block or quarter-mile.