I'll try to explain the science behind the concept, it's not hard to understand, and in fact it makes sense once you hear it explained. The basic premise is the application of what is called "complex training". Complex training combines a high strength movement with a bio-mechanically similar, ballistic or plyometric movement. Squats and jumping jacks would be an example of complex training. For example, do a set of squats with weights and immediately do a set of jumping jacks from a squat position and that would be a complex training movement. This type of complex training has been studied, and shown to be superior to weight or resistance training and plyometric training alone.