To help you make those sprints as effective as possible, we talked to Phil Campbell, an interval-training expert and author of Ready, Set, Go! Fitness. Here are his top fat-burning tips.
1) Warm Up
"You want to take your heart rate up progressively," Campbell says, "Focus on large muscles like the hamstrings and quads. Try ankle circles, knee circles, some light hip stretches—they all get your muscles and ligaments prepared to fire faster."
"The key is to get totally winded in 30 seconds or less," he says, "If you're on a treadmill [or an exercise bike], start sprinting as the machine speeds up. When it reaches top speed, go all out for 30 seconds. Then slow it down and go nice and easy for 90 seconds to recover." If you're running outside, try to cover about 200 feet—roughly half a city block—as fast as possible. Walk slowly for 90 seconds to cool down, then repeat your course.
Almost everyone leans forward when they work out on a cardio machine. This lets you use gravity to pull you forward, making the effort a bit easier. "If you stay upright during your sprints," Campbell says, "it keeps the intensity on your muscles the entire time."
Don't rush into the next exercise before you're ready for it. Your body burns far more calories when your body is forced to transition from a state of rest to a state of full-on activity, and that's tough if you feel like you're running yourself too ragged, too soon, Campbell says.
"Even if you feel like you can go all out again after just 30 seconds, you're still better off waiting the extra minute and then pushing yourself even harder."
"When running outside, start with 50% of your top speed on your first interval," Campbell says. "Go up to 60% or 70% on the next, and so on." Push your body as hard as you can as you get into the groove of the workout.
"You should never feel duty-bound to do two intervals today, three the next time you work out, and four the time after that," Campbell says. "The overall intensity of the intervals you complete is more important than how many you do in any given workout."