Does high intensity interval training (HIIT) have benefits beyond time savings and making workouts more interesting? As the current number 1 fitness trend, HIIT is being heavily studied and lots of compelling data is coming in. When I first heard that post-exercise calorie burning was substantially increased by these workouts, I was skeptical. Dr. Kravitz, however, confirmed that this was true (although perhaps not for 24-36 hours as claimed). He discussed the cell’s need to restore pre-exercise homeostasis by functions such as creatine phosphate replenishment, metabolism of lactate, temperature recovery and hormone restoration among others. He emphasized the extreme cellular disruption of HIIT with the memorable “Kravitz blender” explanation. It is as if the contents of the cells are placed in a blender and in the hours after the workout must be restored resulting in substantial post-exercise calorie burn. Metabolic rate and thus fat burning also increases due to a remarkable increase in the size and number of mitochondria AKA “fat burning furnaces”. Furthermore, measures of cardiopulmonary fitness such as VO2 max increase by up to 46% and factors such as heart contractility and muscle capillary density improve. Aerobically trained athletes typically show dramatic improvements in long distance racing times when they incorporate HIIT. There are too many benefits for one post! I’ll discuss remarkable hormonal and lipid changes on Friday.