AN ESTIMATE OF FORCES AND TORQUES AT THE JOINTS DURING TRAMPOLINE PERFORMANCES

Abstract

During a trampoline performance athletes have to perform ten jumps which include somersaults, twists, and combinations of both. The various postures have to be changed according to the requirement of the specific jump. Needless to say the forces and torques at the various joints caused by centrifugal effect have to be counterbalanced by muscle force. The forces and torques also indicate which of the muscle groups that have to be strengthened and to what extent. In training their athletes, most coaches are guided by their own experience. It is not clear if their method of training strengthens the right muscle group to the right degree. We have, therefore, invented a method to estimate the forces and torques at the joints in the dynamic movements. To get the right animation we use a 3D Peak Performance motion analysis system which delivers the 3D coordinates of important landmarks as functions of time. In addition we produced 2 conversion programs: the first conversion program calculates the relative movement data for the segments according to the Hanavan model, to be used in the SDS software of SOLID DYNAMICS, Roanne, France. As a further input to SDS we use the anthropometric data of 39 measurements for each individual. The second conversion program computes all necessary anthropometric data also according the Hanavan model. Besides data of the correct segment lengths we provide data of the segment mass, the segment center of gravity, the inertia tensors, and the location of the joints. With this input SDS provides an animation of the performance including the forces and torques. In the case of a triple somersault, we determine torques in the hip joints of up to 200 Nm, with the main direction of the torque lying in the lateral axis. But, in the case of a twist, the torque in the spine (asymmetrical posture) has to be balanced by the various trunk muscles. With this method we achieve a better understanding of the muscle activity and thereby a more efficient training program.