"Uncle Willie's" pushups

Last night while leading the conditioning exercises Mr. Rypma said that during the Uncle Willie's exercise one should contract the abdominal. If one were strong enough and performing this on ice the body would jack knife.

This exercise is performed by prone, the forearms on the mat and lifting the body up off the ground so that it is parallel to the floor, weight on the forearms and balls of the feet. It is named for Grand Master Willie Adams.

I use to think that this was an "easy" exercise and an opportunity to rest. Not any more, it's bleeding hard work to pull the elbows to the toes. Can you say isometric? How about dynamic tension?