The HIIT (high-intensity interval training) trend took off this past year for two reasons. First: The workouts are short and sweet, usually requiring no more than 45 minutes of training. Second: They work, especially for that pesky tummy fat everyone’s always trying to tighten up. So it’s only right that HIIT yoga is about to become a lot more popular. By incorporating things like squat jumps and lunges into typical yoga poses, you suddenly burn more calories and feel zen.