A biomechanical analysis of non-linear motion in soccer
Soccer consists of many different types of sports specific movement. The present level of understanding of non-linear motion is negligible yet required if improvements are to be made in technique and performance of such actions. This thesis aimed to establish mechanisms for non-linear motion relevant to soccer performance. Preliminary analysis of curvilinear motion involved electromyographical analysis in selected muscles of the lower extremity at different grades of curvature. Results revealed adaptation of temporal muscle activity at the tightest grade of curvature. Adaptation occurred in both legs, but predominantly the outside leg, with increased duration of activity after footstrike (Smith et al., 1997). Stride kinematics were also altered, as increasing curve severity gave reduced stride length and increased stride frequency. Foot contact time was not changed as a function of curvilinear motion (P > 0.05), giving an increased proportion of the stride cycle in the stance phase. Rear foot contact time increased as a function of curve severity (P $ 0.05). To describe and quantify adaptation of lower limb movement in curvilinear motion, three-dimensional kinematics were used. Subjects (n = 8) wore soccer footwear on natural turf. Ranges of motion at the lower extremity were increased at the faster of the two velocities tested (4.4 and 5.4 ms·] ± 5%), yet tended to reduce with curve severity. The inside leg displayed more differences in angular displacement with curve severity, and the ankle joint showed to be a key adaptive site. Ground reaction forces of two consecutive footfalls were performed on natural turf to assess relative contributions of the two limbs during straight and curvilinear motion at a 5m radius. Total force over two footfalls was greater during straight motion. A mechanism of lowered centre of gravity during curvilinear motion was proposed. During curvilinear motion the outside leg was associated with greater force values in all three planes, displaying a greater contribution to curvilinear motion. Force measurements on natural turf were used to assess different sole configuration during three soccer specific moves. A modern moulded sole was found to be associated with greater maximum friction, also lower vertical ground reaction forces during a Cruyff turn and lower overall forces during the shot. This thesis established biomechanical adaptations and suggested mechanisms during non-linear motion in the soccer player. The research represented the first experimental investigations in this area and therefore recommendations for future study are considered.