PRODUCTION OF ANGULAR MOMENTUM IN DOUBLE SOMERSAULTS
Keywords: gymnastics, somersault, angular momentum, video analysis
AbstractPrevious studies of somersaults in the floor exercise have shown that angular momentum decreases during the ground contact phase of takeoff and that the total angular momentum required to complete a double backward somersault depends on the body configuration adopted by the gymnast in flight (Hwang, et al., 1990; Brüggemann, 1994). The purpose of this study was to examine the relationship between the gymnasts’ actions and the linear and angular momentum in the takeoffs for double backward somersaults. Twelve female gymnasts showing varying degrees of body extension in the flight phase of double backward somersaults were recorded with two video cameras during the floor exercise routines at the Atlanta Olympic Games. The twelve analysed movements were divided into two equal groups of straight (S) and nonstraight (N, tucked and piked) somersaults to investigate relationships between incoming and outgoing momentum values and body configuration changes during takeoff. The Direct Linear Transformation was used to reconstruct the 3D coordinates of the digitised joint centres. Inertia data for each gymnast were derived from a mean data set of gymnasts and were customised to each competitor using estimates of segment lengths from the digitised data. Normalised angular momenta in straight somersaults per second were calculated about a transverse axis through the mass centre using the method of Yeadon (1990). Changes in joint angles and average joint angular velocities at the ankles, knees, hips and shoulders were determined from touchdown to takeoff. RMS differences between the measured locations of the calibration reference points and their predicted location were 0.0073 m horizontally and 0.0026 m vertically. Incoming angular momenta were higher (S = 2.4, N = 2.1, ) and ground contact times were shorter for group S (S = 0.112s, N = 0.125s, ). There were no differences between other incoming variables. For double non-straight somersaults the gymnast changed from a piked to a straight shape during takeoff, whilst for the double straight somersaults the shape change was from piked to arched. Arriving with higher angular momentum at touchdown and arching during ground contact can be understood as techniques that gymnasts employ to achieve a high angular momentum at takeoff. Gymnasts lose angular momentum during the takeoff for all types of double backward somersaults but the rapid arching which occurs during the takeoff for double straight backward somersaults reduces this loss and makes it possible to reach the required high angular momentum value. REFERENCES: Yeadon, M. R. (1990). Journal of Biomechanics 23, 75-83. Hwang, I. et al. (1990). International Journal of Sport Biomechanics 6, 177-186. Brüggemann, G.-P. (1994). Sports Science Review 3; 79-120.
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