High-intensity interval training has been a trending fitness routine for several years. “HIIT is such a big hit because it's the quickest way to burn the most amount of calories you can in a short amount of time,” according to Famisha J-Millman, a Master Personal Trainer and owner of Glisten Girls Fitness, because this type of training can literally transform your body. Interval training has proven to burn more calories because of the exchange of oxygen and carbon dioxide by the body. Also, it takes longer to recover after an HIIT workout, which means you’re still burning calories even though you’re not exercising.