The effect of surface geometry on soccer ball trajectories

Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five professional players are observed using high-speed video when taking curling free kicks with four different soccer balls. The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s. It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated. Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free kick by up to 1 m.     

Boot-insole effects on comfort and plantar loading at the heel and fifth metatarsal during running and turning in soccer

Plantar loading may influence comfort, performance and injury risk in soccer boots. This study investigated the effect of cleat configuration and insole cushioning levels on perception of comfort and in-shoe plantar pressures at the heel and fifth metatarsal head region. Nine soccer academy players (age 15.7 ± 1.6 years; height 1.80 ± 0.40 m; body mass 71.9 ± 6.1 kg) took part in the study. Two boot models (8 and 6 cleats) and two insoles (Poron and Poron/gel) provided four footwear combinations assessed using pressure insoles during running and 180° turning. Mechanical and comfort perception tests differentiated boot and insole conditions. During biomechanical testing, the Poron insole generally provided lower peak pressures than the Poron/gel insole, particularly during the braking step of the turn. The boot model did not independently influence peak pressures at the fifth metatarsal, and had minimal influence on heel loads. Specific boot-insole combinations performed differently (P < 0.05). The 8-cleat boot and the Poron insole performed best biomechanically and perceptually, but the combined condition did not. Inclusion of kinematic data and improved control of the turning technique are recommended to strengthen future research. The mechanical, perception and biomechanical results highlight the need for a multi-faceted approach in the assessment of footwear.     

K-ABC and McCarthy scale performance among “at-risk” and normal preschoolers

This study assessed the degree of comparability between the McCarthy Scales of Children's Abilities (McCarthy) and the Kaufman Assessment Battery for Children (K-ABC) for 51 “at-risk” (Low Birthweight, Head Start, and Developmentally Delayed) and 33 “normal” preschool children. The K-ABC Mental Processing Composite (MPC) and McCarthy General Cognitive Index (GCI) correlated significantly for both groups, but was significantly greater for the at-risk preschoolers. The at-risk group achieved a significantly higher mean MPC than GCI, while the normal comparison subjects achieved a slightly lower mean MPC. As reflected in previous studies, the GCI seems to provide an accurate estimate of the at-risk child's typical classroom performance. While the MPC may afford an estimate of such children's capacity for academic growth, if provided appropriately tailored remediation, it may also be missing critical aspects of children's cognitive functioning. Mean score discrepancies for at-risk preschoolers were discussed in relation to the theoretical and psychometric properties of the K-ABC and McCarthy.