This Is the Workout That Gives the Fastest Results, According to Science

Maybe you haven't set foot inside a gym in months, and you shudder at the thought of running on a treadmill or lifting weights. Or maybe you're a seasoned gymgoer who's hit a plateau in your progress. No matter your fitness persona, there's one thing we all have in common: When we're ready to get in shape, we want it to happen quickly. Overnight would be nice, but we're not The Hulk, so we've got to get real. The best way to do that is to rely on science (because busting our humps at the gym is a wash unless we're doing it correctly).

In our quest to find the workouts that will get us toned the quickest, there was one underlying commonality in each study: high-intensity interval training (or HIIT).

First, let's define what we mean by "getting in shape." We're classifying this as increased muscle definition and general physical performance, aka having a more toned physique and being able to climb the stairs at work without gasping for air. So how can you do this in the shortest amount of time? Studies suggest that swapping out endurance workouts for HIIT (short bursts of intense cardiovascular exercise alternated with less intense recovery periods) yields the same cardiovascular and muscular benefits in half to one-third the time.

In one particular study, 27 subjects were split into two groups—endurance training and HIIT—and took part in their separate training regimens for a series of weeks. At the end of the study, the HIIT group lost three times as much body fat as the endurance-training group, even though they burned almost half as many calories (which goes to show that the calorie counter on your treadmill shouldn't be your measure of success).

Busy people, rejoice: One hour of high-intensity exercise over the course of a week will lead to greater fat-melting results than 150 weekly minutes of moderate-intensity activity. So while you'll have to push yourself harder for those short intervals, you won't have to work out as long.

But before you lace up your Nikes and head for the treadmill, know this: Yes, running at sprint and recovery intervals will help you burn more fat than you would with a steady jog, but Jessica Matthews, an exercise physiologist with the American Council on Exercise, says you'll reap the most benefits of HIIT from full-body exercises like burpees, kettlebell swings, plank-ups, etc., which we've outlined for you below.

Ready to lose more fat in less time? Keep scrolling for some of the best fat-blasting HIIT workouts.

For Your Buns

Grab some dumbbells for this set: In between star jumps, burpees, and running, you'll do some weighted squats for a more sculpted booty. (Bonus: You're working a ton of other muscles in the process, too.)

For Your Abs

Psst: For this set, you'll need a yoga mat. These ab-chiseling moves are alternated with squat pops, jumping jacks, squat jumps, etc., for maximum results.

For Your Legs

All you need for this set is a chair or a bench to place your legs on. The cardio moves are intense, but the easier, low-intensity intervals make the workout more bearable.

For Your Upper Body

This set requires a bit more equipment—like these C9 Neoprene Hand Weights ($4), a yoga mat with grip, and a stepper. After alternating dumbbell curls and cardio consistently, you'll have Michelle Obama arms—we promise.

Before beginning a fitness regimen, please consult your doctor.

Up next, read the seven things you should never do after you work out.

This story was originally published at an earlier date and has been updated.