In vertical and long jumping, the takeoff foot is planted firmly. The spring comes from the extension of the take-off foot leg as the other leg reaches for the high or far side of the obstacle (like a ditch). The arms are forcibly raised forward and upward to assist in propelling the body. Landing may be on one or both feet, depending upon the length of the jump. When jumping downward from a height, the jumper should aim his feet at the desired landing spot and jump with the knees slightly bent, feet together, and the trunk inclined slightly forward. As the feet strike the ground, the shock is absorbed by bending the knees into a full squatting position. If the height is too great or the ground too hard to absorb the shock, the jumper should execute a forward or side roll to absorb some of the shock.