Flight Phase Joint Control Required for Successful Gymnastics Landings

Abstract

Introduction The mechanical goal of a gymnastics landing performed during competition is to reduce the total body vertical, horizontal, and angular momentum at touchdown to zero without moving their feet (Federation Internationale de Gymnastique, 1984). The reduction in total body momentum at contact is achieved by the net impulse applied by body weight and the reaction force during foot contact with the surface. The momentum and position of the body at touchdown will influence the ability of the gymnast to distribute load and reduce total body momentum. Prior to touchdown, gymnasts must control their total body moment of inertia so that they initiate contact in an advantageous position for generating the impulse necessary to reduce total body momentum. This study uses experimental and modeling techniques to test the hypotheses that 1) gymnasts use the same flight phase lower extremity multijoint control during successful and unsuccessful landings and 2) modifications in flight phase shoulder joint control would be sufficient for producing initial conditions at contact that would ensure performance of a successful landing. Methods Successful and unsuccessful layout saltos dismounts from asymmetrical bars performed by a female gymnast during the 2000 Olympics Artistic Gymnastics Competition were videotaped (3D, 200Hz, NAC C2S). Body landmarks (deLeva, 1996) were manually digitized and 3D data were computed (Motus, Peak Performance) during the flight phase (∼0.2s, 1/2 body rotation) prior to contact. Sagittal plane kinematics were then digitally filtered and differentiated using quintic splines (Woltring, 1986). The equations of motions of a planar 5-segment system Figure 1) during flight was formulated (Maple) using LaGrange's method and dynamically simulated using ADAMS (Mechanical Dynamics) and Matlab/Simulink (Mathworks). Model initial conditions were determined from both landings while input joint moments were calculated from the unsuccessful landing. Modified landings were simulated by systematically scaling the shoulder, hip, knee, and neck joint moments of the unsuccessful anding. The R-angle (formed by a line from the ankle to total body center of mass relative to right horizontal) at contact were computed and used as indicators of landing success. Results A five-fold increase in the shoulder joint moment of the previously unsuccessful landing resulted in a 0.26rad change in R-angle at contact (Figure 2). This change in shoulder joint moment was needed to position the TBCM at an R-angle necessary for generating the impulse needed for a successful landing performance. Modification of the neck, knee, and hip joint moments resulted in unrealistic joint angles at touchdown.Figure 1Figure 2Discussion High velocity landing tasks presents a potential conflict between the need to achieve a desired performance land without a hop or step) and self-preservation (avoid critical tissue limits). Modification of the trunk-arm ubsystem may be an effective mechanism for controlling total body moment of inertia in preparation for landing without inducing a modification in lower extremity control or mechanical loading after foot contact. Further studies will need to be done to determine if scaling of the shoulder moment during flight is a feasible compensatory mechanism to ensure safe and successful landings. Advancement in our understanding of landing control structures will facilitate development and evaluation of new methods for improving landing performance. Acknowledgements IOC Medical Commission, ISB Student Diltation Award Inte