Wondered what peoples opinion on one of the modern approaches to butterfly is, which is that the torso and upperbody says as streamlined and flat as possible with only the legs kicking in a narrow window to keep the hips up. Certainly USRPT do much to distance themselves from full body undulations due to the increased drag. They use language such as 'double leg kick' instead of dolphin kick. This could also be why we are seeing more and more fly swimmers breathing to the side.
This video is the last in a series of USPRT butterfly focus points or 'microcycles'
As an aside USRPT has much in common with TI such as the constant repetitions at the desired pace and stroke length as they are big believers in building the neurological pathways so that training is always relevant to racing.