their feet. As technology enabled higher vaults, mats evolved into bags of large chunks of foam. Today's mats are foam usually thick. They are usually built up with two cross-laid square section logs with gaps between them, topped by a solid layer of foam of the same thickness. This lattice construction is wrapped in a close-fitting cover topped with nylon mesh, which allows some air to escape, thus combining both foam and a measure of air cushioning. The final layer is a large mat of mesh-covered foam which is clipped around the edges of the complete pit and prevents the athlete from falling between the individual bags. Mats are growing larger in area as well to minimize risk of injury. Proper landing technique is on the back or shoulders. Landing on the feet should be avoided, to eliminate the risk of injury to the lower extremities, particularly ankle sprains. Rule changes over the years have resulted in larger landing areas and additional padding of all hard and unyielding surfaces. The pole vault crossbar has evolved from a triangular aluminum bar to a round fiberglass bar with rubber ends. This is balanced on standards and can be knocked off when it is hit by a pole vaulter or the pole. Rule changes have led to shorter pegs and crossbar ends that are semi-circular. Technique Although many techniques are used by vaulters at various skill levels to clear the bar, the generally accepted technical model can be broken down into several phases. Approach During the approach the pole vaulter sprints down the runway in such a way as to achieve maximum speed and correct position to initiate takeoff at the end of the approach. Top class vaulters use approaches with 18 to 22 strides, often referred to as a "step" in which every other foot is counted as one step. The run-up to the vaulting pit begins forcefully with the vaulter running powerfully in a relaxed, upright position with knees lifted and torso leaning very slightly forward. The head, shoulders and hips are aligned, the vaulter increasing speed as the body becomes erect. The tip of the vaulting pole is angled higher than eye level until three paces from takeoff, when the pole tip descends efficiently, amplifying run speed as the pole is planted into the vault box. The faster the vaulter can run and the more efficient their take-off is, the