Interval training involves alternating between high intensity exercise bursts and lower intensity recovery periods. It has been shown to burn more calories and fat both during and after a workout compared to steady-state cardio. The afterburn effect causes increased calorie and fat burning for up to 48 hours after interval training. It also improves cardiovascular fitness and metabolic rate more quickly than traditional cardio. Effective interval training uses different ratios of high to low intensity periods tailored to one's fitness level.