7 Ways to Get a Better Body in 30 Minutes or Less

While exercise scientists are still trying to figure out exactly how many (or how few) sprints we need to do to get optimal effects, and how many seconds each interval should last, they all agree that any amount of time is better spent moving than sitting. "We know that all-out intervals—like you're sprinting to save a child from a burning car—produce a calorie burn that persists even when you're sitting down," says exercise physiologist Martin Gibala, PhD, the chair of the department of kinesiology at McMaster University in Hamilton, Ontario (and one of the leading HIIT—high-intensity interval training—researchers). "But we don't know enough yet to say how much better that would be than a four-minute all-out sprint without breaks." So, if you've got a few extra minutes and are feeling physically spry but too mentally fried to remember how many jump-squats you need to do in what amount of time, Gibala suggests running up and down the stairs or doing a lap around the parking lot—you'll burn 50 to 75 calories.