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 take-off 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, he or she will overrotate on subsequent jumps and probably fall. The way that skaters control rotation differs depending upon the nature of the landing and take-off 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 take-off of the jump that follows it, the bend on the landing leg of the first jump serves as preparation for the spring of the take-off of the subsequent jump. If some time elapses between the completion of the first jump and the take-off of the subsequent one, or if a series of movements serve as preparation for the subsequent jump, the leg bend for the spring can be separated from the bend of the landing leg.