You've long taken advantage of intervals' fat-incinerating benefits, and tweaking your hard-easy program can help you sweat off even more in even less time. In a University of Copenhagen study, researchers had adults replace their regular training sessions with 20- to 30-minute runs of gradually building 1-minute repeats consisting of 30 seconds jogging, 20 seconds moderately paced running, and 10 seconds sprinting. Although the runners cut their training time in half, they also cut 23 seconds from their 1,500-meter runs and a minute off their 5K times. Plus they significantly lowered their blood pressure and cholesterol levels, all in just seven weeks.
This type of up-down intensity also melts serious calories. "These workouts cause your heart rate to race up and down, so your body never adjusts to the workout and therefore continues to burn more calories than it would if going at a single pace," says Taylor Ryan, a certified personal trainer and nutrition consultant in Charleston, SC. The metabolism boost can last for up to 48 hours post-workout. In fact, studies have shown that two hours of intervals is equivalent fat-burning wise to 10 hours of steady-state cardio when both are performed over the course of two weeks.
Ryan recommends using the 10-20-30 formula for your runs three to four non-consecutive days a week. It works for walkers too: Use a brisk pace for 30 seconds, speed walk 20 seconds, and go as fast as you can for the last 10 seconds.