Kazutoshi Kobayashi

Two-dimensional cushioning characteristics of sports surfaces

To evaluate sports surfaces, organizations often adopt vertical force attenuation or deformation and horizontal friction tests. Impact attenuation of sports surfaces is especially important for injury prevention. Although the mechanical tests are reproducible and the criteria for these tests are very strict, they have an issue of ‘particularity’: that is, the material behaviour may change when the mechanical properties of the drop mass spring systems are changed. To avoid this, we proposed an evaluation method using a mathematical surface model and computer simulation in previous studies that examines vertical properties only, while a two-dimensional impact test device for examining the two-dimensional cushioning characteristics of sport surfaces using a parallelogram linkage was proposed in previous studies. In this study, the data acquired from the two-dimensional device was confirmed by high-speed video. We then conducted two-dimensional impact tests – 69 trials, including 5 slip trials – using a variety of impact intensities and impact angles. The conclusions are as follows: 1) The impact force and the displacement acquired from the device were reliable even in slip trials; 2) When comparing the impulse of non-slip trials and slip trials, horizontal cushioning was observed in the slip trials, especially in the higher drop height group; 3) Even in non-slip trials, two-dimensional cushioning of impulse was observed; and 4) The impact friction test used in this experiment is significantly different from the popular friction tests and can provide new knowledge about the cushioning and friction characteristics of sports surfaces.

Estimation of Actuating Force of Running by Viscoelastic Model with a Characteristics of Muscle.

Although a balls rebound height decreases for every fall, a mans rebound height in running is kept constant by supplying the actuating force in a certain amount through the ground reaction force of landing. Purpose of this study is to propose an estimation method of the actuating force from the ground reaction force. In this paper, the mechanical model of running is represented by the mass-nonlinear Voigt model which is composed of the nonlinear spring element whose stiffness decreases with time because of the biomechanical properties of passive tension of muscle and the nonlinear damping element which is expressed by polynomial of viscous element and some elastic-viscous interactive elements. In this model, when the resultant reaction force of the viscous and interactive elements agrees with the velocity of mass center in direction, the force is estimated as the actuating force.

Mechanical Model of Head Imapact during Sports Activity

Brain injuries during sports activity are caused by percussion which involves collision to the head. Constructing a protective environment for such collisions is one of the most important problems in biomechanical research. In this investigation, we calculated the impact force to the head with computer simulation, and evaluated the limitation speed for perpendicular and oblique impact to sports fence. From the evaluations, we suggested that safety is not always higher when the shock absorption is higher. There is a moderate capacity of the shock absorption.