From the perspective of the Riding Tree's progressive skill levels, releasing a horse over a jump is a simple matter of rhythmically riding a relaxed horse with what I call 'connection.' Connection is a circle of energy flowing from the horse's contracted abdominal muscles, through thrusting hind limbs, over a lifted back, into the bit and, finally, connecting to the rider's hands. When they are connected, horse and rider approach, jump and land over a fence smoothly and effortlessly.
This is just what I found :) you can definitely do some research on the internet to get all sorts of perspectives. Here’s the article I was on http://www.meredithmanor.edu/features/articles/nancy/releasing-over-jump.asp