I am using the word Trunk more and more as I find the use of the word core over used and biased towards abdominal muscles. Many of the experts are focusing on anti-rotation and that is far from effective than focusing on quality gyroscopic action of the core. A great observation from Steve (hurdlesfirst.com) is the fact the lead arm in hurdling is always moving because it's always working. The core is about redirecting forces specifically and not anti-rotation. In fact this is the problem with people doing kneeling core chops thinking they are plugging "energy leaks" and other buzz phrases. The exercises are many times fine but I am more buyer into the Cuban and French approach. Coach Santiago does many of his drills without extremities in order to challenge the trunk and the gymnastic exercises by the french 100 years ago are perfect for small and large group settings. I find the exercises that are done now of use but they are many times very static and poor in transfer. You may test well with the PT but the high speed camera's don't lie when you are up on your feet in ballistic activity.