With its fusion of HIIT, circuit, and functional training [1], F45 promises the "most effective workout method for burning fat and building lean muscle." But just how many calories will you burn in any one of the studio's unique classes? We asked Sam Cosner, head trainer at F45 in Sarasota, FL [2].

"In general, our clients can expect to burn 300 to 1,000 calories during a 45-minute workout," Cosner told POPSUGAR. But there are many factors that may influence that number. "Muscle mass, age, gender, and intensity all play a role in total calories burned [3]," she continued.

Cosner also stressed that calorie burn isn't the only measurement of a good workout. Each of the 31 classes offered at F45 is different. Some workouts are more resistance-focussed, while others are centreed on intense cardio — and generally, the goal of strength training is not to burn more calories, but to lift as much as you can [4], she explained.

Here's the awesome thing about those high-intensity intervals, though: Cosner said a client can expect to burn calories for up to 36 hours after a class has ended, depending on the workout and the length of the rest and work periods. Whatever your goal — to torch calories, boost metabolism, or reduce body fat [5] — talking to an F45 trainer 1-on-1 can help you make sure you're on the right track.