Laboratory assessment of a head impact sensor for youth soccer ball heading impacts using an anthropomorphic test device

Recent advances in technology have enabled the development of instrumented equipment, which estimate the head impact kinematics of athletes in vivo. One such headband-mounted impact sensor is the SIM-G (Triax Technologies, Norwalk, CT, USA), which has been previously used to investigate the biomechanics of soccer heading by human subjects. Previous studies have evaluated the accuracy of the SIM-G for pure rotation and pendulum, impulse hammer and drop rig impacts. The current study used a soccer ball heading model to evaluate the accuracy of the SIM-G. A soccer ball was projected at the head of an anthropomorphic test device (ATD) representing a 10-year-old to replicate the heading maneuver at various impact sites, angles and speeds previously identified in youth soccer. Linear regression revealed that the SIM-G sensor overestimated the peak angular velocity and linear acceleration recorded by the ATD headform by approximately 44% and 105%, respectively. Tests in which the ball directly contacted the SIM-G sensor resulted in the largest peak linear accelerations. Glancing impacts were significantly associated with a decrease in percentage error of the SIM-G sensor peak angular velocity data relative to the ATD reference data. While it may not demonstrate accuracy in estimating the magnitudes of head impacts, the SIM-G remains a useful tool to provide estimates of head impact exposure for soccer players.

Aerodynamic Differences between New and Used Soccer Balls

The surface structure of soccer balls, such as the number and shapes of the ball panels, has recently changed, and research on the aerodynamics and flight trajectories of new soccer balls is actively proceeding. However, these studies are focused on new soccer balls, whereas the used soccer balls were never studied. In this study, the aerodynamic characteristics of soccer balls kicked 1000 times by a robot were investigated through wind tunnel tests. The results were compared with those obtained using new soccer balls. Regarding the aerodynamic characteristics of the soccer balls, it was found that the critical Reynold number, Recrit, changes with usage. This is related to the transition from laminar to turbulent flow of airflow around the ball. The comparison of the drag coefficients of the balls at Recrit showed that the drag coefficients of the new and used Telstar18 balls were 0.15 (Re = 2.5 × 105) and 0.14 (Re = 2.2 × 105), respectively; those of the new and used Merlin were 0.13 (Re = 2.8 × 105) and 0.13 (Re = 2.2 × 105), respectively; and finally, those of the new and used Derbystar were 0.14 (Re = 2.1×105) and 0.14 (Re = 2.1×105), respectively. The surface conditions of a soccer ball, such as the surface roughness and surface damages, are essential factors to determine the aerodynamics of the soccer balls.

DEVELOPMENT OF PASSING ACCURACY TRAINING MODEL ON FOOTBALL PLAYING SKILLS IN SCHOOL STUDENTS FOOTBALL YEAR 2020

This study aims to develop a form of training model for passing accuracy in soccer. The population in this study were all soccer athletes from Postab, PTPN II and Sinar Pagi. The form that has been made in advance is validated by 3 experts, 1 soccer ball coach, 1 expert in sports and 1 expert in the field of language, where the percentage of validity is 86% which is taken from the smallest to the largest percentage value of the overall results. The method used is the research and development method (Research and Development / R&D). The results of the small group test involving 3 experts consisting of 1 expert trainer, 1 linguist and 1 sports academic showed that the 20 variations of the exercise had met the proper criteria. The percentage of validity of the questionnaire that has been distributed to the sample shows that 88% is taken from the smallest to the largest percentage value of the overall results. The results of a large group test of 6 experts consisting of 2 expert trainers, 2 linguists and 2 sports academics showed that the 20 variations of the exercise had met the criteria worthy of use. The percentage of validity of the questionnaire that has been distributed to the sample shows that 90% is taken from the smallest to the largest percentage value of the overall results. It can be concluded that the 20 training variation models are good for increasing the ability of passing accuracy in soccer and training to be more interesting, because this is very important in training so that the exercise is not boring and becomes input for coaches in football clubs throughout Indonesia.