Best Cardio Ever: 15 Ways to Make It Really Work

Burn Double the Calories

"When you run fast, then slow, then fast again, you burn more calories, because on average, you're moving more quickly than you do during a steady walk," says Holland. Start with a five-minute warm-up, then intersperse a one-minute burst of intensity followed by two minutes of easy running or walking; repeat five times. You can also do longer, distance-based intervals: If you have access to a track nearby, walk (or run) fast on the straightaways and then slow down and go easy on all the curves.

If you typically stick to the treadmill, mix it up and run or walk outside at least once a week. "Factors like wind and varying terrain force your body to work harder and burn more calories," says Holland. On the other hand, if you mostly run or walk outside, hop on the treadmill every now and then -- it's much more difficult to cheat your speed and intensity while on the belt.

"When walking, try to take at least 40 steps every 20 seconds," says Fenton. "Once you become totally comfortable at this faster pace, shoot for 45 and then 50, even if you can maintain the speed for only a few minutes. "By putting more zip in your step, you can burn about 100 more calories in a 30-minute walk than you usually do."

Walking with Nordic poles could help you blast up to 50 percent more calories per hour than usual. "You'll sculpt your triceps, lats, chest, and shoulders -- plus, you'll feel your abs contract with every stride," says fitness expert Kathy Smith.

"Doing hill repeats -- running fast up a hill and then jogging slowly back down to recover -- can increase your calorie burn by up to 50 percent," says Holland. If you don't have a hill nearby, run up and down local stadium or park steps instead. Try to work 5 to 10 hill repeats into one of your runs or walks each week.