the increase of back injuries. Since the tendency of an edge is toward the center of the circle created by that edge, a skater's upper body, arms, and free leg also have a tendency to be pulled along by the force of the edge. If the upper body, arms, and free leg are allowed to follow passively, they will eventually overtake the edge's rotational edge and will rotate faster, a principle that is also used to create faster spins. The inherent force of the edge and the force generated by a skater's upper body, arms, and free leg tend to increase rotation, so successful jumping requires precise control of these forces. Leaning into the curvature of the edge is how skaters regulate the edge's inherent angular momentum. Their upper body, arms, and free leg are controlled by what happens at the time of preparation for the jump and its takeoff, which are designed to produce the correct amount of rotation on the takeoff. If they do not have enough rotation, they will not be at the correct position at the takeoff; if they rotate too much, their upper body will not be high enough in the air. Skaters must keep track of the many different movements and body positions, as well as the timing of those movements relative to each other and to the jump itself, which requires hours of practice but once mastered, becomes natural. The number of possible combinations jumps are limitless; if a turn or change of feet is permitted between combination jumps, any number of sequences is possible, although if the landing of one jump is the takeoff of the next, as is the case in loop combinations, how the skater lands will dictate the possibilities going into subsequent jumps. Rotational momentum tends to increase during combination jumps, so skaters should control rotation at the landing of each jump; if a skater does not control rotation, they will over-rotate on subsequent jumps and probably fall. The way skaters control rotation differs depending upon the nature of the landing and takeoff edges, and the way they use their arms, which regulate their shoulders and upper body position, and free leg, which dictates the positioning of their hips. If the landing on one jump leads directly into the takeoff of the jump that follows it, the bend on the landing leg of the first jump serves as preparation