Science of HIITSee under the skin of 90+ HIIT exercises and take your workouts to the next level. Get the best results from your HIIT workouts by understanding the muscle action needed to perfect each exercise. Explore the physiology of more than 90 essential HIIT exercises, to master each movement with confidence and control. Recent scientific research shows that HIIT is the most efficient form of exercise for raising fitness levels, increasing cardio respiratory