Biomechanics of the spine in the polevaulter as related to spondylolysis.

An athlete was filmed at high speed to anatomically plot the position of the vertebrae during several pole vaults. A computer analysis adapted from a previously described program (Gainor, BJ, et al: The kick: Biomechanics and collision injury. Am J Sports Med 6: 185-193, 1978) was used to quantify the kinematic data. The thoracic and lumbar vertebrae of the polevaulter began in a neutral position but rapidly hyperextended 40 degrees during pole plant. The spine subsequently flexed 130 degrees in 0.65 seconds as the pole uncoiled and the athlete was propelled towards the bar. Angular velocities of the spine reached a maximum of 6 radians/sec during both extension and flexion. More significantly, angular accelerations of 150 radians/sec2 occurred in hyperextension, and 180 radians/sec2 in hyperflexion. Torque about the spine was estimated to be 1,500 inch-pounds during extension and 1,800 inch-pounds during flexion. The maximum kinetic energy in the athlete's body was calculated to be 36,000 inch-pounds. We believe the magnitude of these torques and accelerations predispose the back to injury. These results were correlated with several cases of spondylolysis in competing polevaulters.