include: the throw Axel, the throw Salchow, the throw toe loop, the throw loop, the throw flip, and the throw Lutz. The throw triple Axel is a difficult throw to accomplish because the woman must perform three-and-one-half revolutions after being thrown by the man, a half-revolution more than other triple jumps, and because it requires a forward takeoff. The speed of the team's entry into the throw jump and the number of rotations performed increases its difficulty, as well as the height and/or distance they create. Pair teams must perform one throw jump during their short programs; senior teams can perform any double or triple throw jump, and junior teams must perform a double or triple toe loop, flip, or Lutz. If the throw jump is not done correctly, including if it has the wrong number of revolutions, it receives no value. Pair teams must perform at least two different throw jumps with a different number of revolutions in their free skating programs. A throw jump is judged as a jump with a higher number of revolution if it is over-rotated more than a quarter revolution; for example, if a pair attempts a double throw jump but over-rotates it, the judges record it as a downgraded triple throw jump. Execution According to Kestbaum, jumps are divided into eight parts: the set-up, load, transition, pivot, takeoff, flight, landing, and exit. All jumps, except for the Axel, are taken off while skating backward; Axels are entered into by skating forward. Skaters travel in three directions simultaneously while executing a jump: vertically (up off the ice and back down); horizontally (continuing along the direction of travel before leaving the ice); and around. They travel in an up and across, arc-like path while executing a jump, much like the projectile motion of a pole-vaulter. A jump's height is determined by vertical velocity and its length is determined by vertical and horizontal velocity. The trajectory of the jump is established during takeoff, so the shape of the arc cannot be changed once a skater is in the air. Their body absorbs up to 13–14 g-forces each time they land from a jump, which sports researchers Lee Cabell and Erica Bateman say contributes to overuse injuries and stress fractures. Skaters add variations or unusual entries and exits to jumps to increase difficulty. For example, they will perform a jump with one or both arms overhead or