DIRECT FORCE MEASUREMENT OF THE VAULT TAKE OFF IN GYMNASTICS

INTRODUCTION The inverse dynamic approach to force measurement of. high speed human movement is susceptible to large second derivative errors, caused by the high sampling rate required to avoid aliasing. In gymnastics vaulting the springboard contact phase has a duration of approximately 0.11 s, Dillman et al (1985). The purpose of the study was to investigate the nature of the forces involved in the springboard take off in vaulting. Kistler Piezo electric load cells (Model 9134a) were selected for direct force measurement of the processes taking place during the take off. Ta work efficiently, load cells must be pre loaded in a mounting jig to provide an inelastic structure through which the forces are transmitted. These jigs were inserted between the upper surface of the springboard (Gymnova Model B219) and the spring and also under the foot at the rear of the board, as can be seen in the figure below.The subjects were eight male gymnasts (mean mass 47.5Kg) who were all members of the Under 15 British gymnastics squad. Following habituation, the gymnasts performed five handspring vaults, replicating competition conditions. The four load cells were preloaded to 10,OOON and attached to the springboard, which was bolted onto a rigid steel plate. The whole structure was bolted to a force platform. Force data was captured at approximately 800Hz on an IBM PC, from immediately prior to contact with the springboard through to several seconds after take off. Each trial was also filmed at 250pps, using a Kodak Ektapro High Speed Video system. Each of the three data channels were smoothed using a 3 point moving average before analysis. RESULTS The figure displays a typical force trace. CONCLUSIONS The mean peak ground reaction force (G.R.F) across all trials was equivalent to 10.6 times body mass (5053N). The mean contact time for all trials was 0 133s, which was in agreement with other published work. The data from Cell 1+2 (summation of front load cells) displayed the double oscillation of the upper surface of the board visible from the video tape, but with an apparaent forward time shift. All three traces revealed a secondary peak in many trials which was attributed to the start of the knee and ankle extension. REFERENCES Dillman.C, Cheetham.P & Smith.S (1985) A Kinematic Analysis Of Men's Olympic Long Horse Vaulting, International Journal Of Sports Biomechanics, 1, pp96-11 O