These 45-minute classes work your cardio system as well as a whole-body workout. Short Intervals of working at your hardest followed by rest maximises calorie burning to achieve those weight loss goals. For the first few hours after a HIIT session EPOC is at its highest and some studies have shown it to continue for as long as 38 hours. This means you continue to burn energy in order to recover from the session for a much longer time after it finishes, which is why HIIT is such an effective exercise for fat burning.