The various counter-pressures result in a locked or jammed hand, which can be very secure when properly placed. The second method involves torquing and camming the appendage in a bottleneck or constriction in the crack. In wide cracks, the limbs are often twisted or stacked and in very wide cracks you'll find that wedging and cross-pressures are the only way up. Halfway between pure crack climbing and pure face climbing, thin cracks require techniques from both forms. Consequently, finger cracks are often technically demanding.
Most climbers think hand cracks are the last word in crack climbing.
A typical lieback will find your side flush against the wall. Your hands are clasping the near edge of the crack, and you are liebacking off them. Your hand are pulling directly out and your feet are pushing the opposite way, directly against the face or far wall. Since the technique is strenuous try to keep the arms straight, which again lets the skeleton, rather than the muscles, absord at least some of the strain. Essentially, your body is like a spring lodged between two sloping walls.