Skaters accomplish edge jumps by leaving the ice from any of their skates' four possible edges; lift is "achieved from the spring gained by straightening of a bent knee in combination with a swing of the free leg". They require precise rotational control of the skater's upper body, arms, and free leg, and of how well he or she leans into the take-off edge. The preparation going into the jump and its take-off, as well as controlling the rotation of the preparation and take-off, must be precisely timed.