Involves doing short intervals of explosive exercises interspersed with short intervals of rest. The exercises include power cleans, snatches, jump squats and kettlebell swings, among others, all of which are typically executed in order to develop explosive power, strength and speed for sports performance. The foundations of the Insanity program build on the principles of HIIT. HIIT stands for High-Intensity Interval Training. The HIIT concept is nothing new, although it is popular at present. It also shares some similarities with Fartlek training. Fartlek training started in 1937 and utilizes the concept of interval training. HIIT training typically combines high energy and low energy exercise performed in intervals. The foundations of the Insanity program build on the principles of HIIT.