MECHANISMS RESPONSIBLE FOR UNDERTWISTING IN THE BAR CLEARANCE OF HIGH JUMPING

Abstract

A high jumper's airborne motion is a twisting somersault. The twist is the combined result of angular momentum acquired prior to takeoff and of action and reaction rotations in the air (“catting”). Some athletes are undertwisted at the peak of the jump, with the hip of the lead leg lower than the hip of the takeoff leg. This reduces the effectiveness of the bar clearance. This project compared 10 undertwisted high jumpers (5 male, 5 female) with 10 normal high jumpers (5 male, 5 female) to find the causes of the undertwisting. Three-dimensional coordinates of 21 body landmarks were obtained for the airborne phase using the DLT method. The catting rotation was separated from the rotation produced by the angular momentum through the use of a rotating reference frame RH that somersaulted with the longitudinal axis of the athlete, and twisted about the longitudinal axis at the angular velocity produced by the twisting component of angular momentum. The twisting angular velocity of the hips relative to RH indicated the angular velocity of catting. Its value was integrated between takeoff and the peak of the jump to calculate the cumulative twist angle change due to catting. The results showed that undertwisting was not due to problems in the twist orientation of the hips at takeoff, but to deficiencies in the subsequent rotation in the air. In four of the five men, the undertwisting was due to decreased catting. In four of the five women, it was due to insufficiency in the twist rotation produced by the angular momentum, ultimately traced to an excessive backward lean at the end of the takeoff. The results of the project suggest that in many cases the correction of undertwisting may be achieved in men through the improvement of catting, and in women through the achievement of a more vertical position at the end of the takeoff. Supported by grants from the U.S. Olympic Committee and USA Track & Field