If you want to burn an absolutely monstrous number of calories in a single workout—we're talking 500 calories or more—then the name of the game is intensity.

"To burn calories, it's important to focus on your own rate of perceived exertion, and to try to keep your heart rate between 75-90% of your max," says Liz Lowe, C.S.C.S., head program designer at Scorch Fitness, a high-intensity interval training gym in Sarasota, FL.

There are a number of ways to keep your heart rate that high—try cardio finishers, plyometrics, resistance moves, and bodyweight exercises, says Holly Perkins, C.S.C.S., Los Angeles-based trainer and author of Lift To Get Lean. "One is not better than another," she says.

Adding sprints, explosive bodyweight exercises, and/or high-rep cardio moves can help spike your heart rate at the end of your workout, too, when your muscles are nearly spent. Workout finishers push your heart to the max faster because you’ve burnt up most of your strength and energy—and that in turn means you burn calories at a faster rate, Lowe says.

Of course, cardio isn't the only way. “By incorporating weights into your HIIT routine, you not only burn 500 calories during your session, but also create more of an after-burn effect known as EPOC, which can increase calorie burn for up to 24-48 hours post-workout,” Lowe says. “By adding resistance training to HIIT, you’ll also gain lean-looking muscle, and increase your metabolism so your body can burn more calories at rest.”

To help get you to that fat-incinerating sweet spot, Lowe and Perkins have compiled seven fat-burning HIIT workouts to help lean out your physique.

The first three are courtesy of Perkins. You can add these workouts, every other day, to your existing weekly strength-training routine.

The last four come courtesy of Lowe. These workouts are meant to be done on four consecutive days, with one to two rest days at the end of the cycle. Perform these workouts for up to four weeks, then switch things up. “If you feel like your recovery is lacking and you’re getting more fatigued by the end of the week, then split the workouts up: two days on, one day off; 2 days on, 1 day off,” Lowe says. “This workout program is intense and not intended to be paired with exercise other than light yoga or long, slow-distance running as active recovery.”