The discussion includes the explanation of the general pattern of the Fz- and Fy- time traces an dthe change in magnitude of the Ground Reaction Force (GRF) variables between each running speed.
The paper aims to investigate the effect of increasing running speed on ground reaction force (GRF) related variables. According to the Newton's Law of Gravitation, any two objects with masses attract each other and the magnitude of this attracting force is proportional to the product of the masses and inversely proportional to the square of the distance. The gravitational force acted upon an object by the earth is called gravity or weight of the object. Since we always have contact with the ground due to this gravity there is always an interaction between our bodies and the ground. The reaction from the ground is called the Ground Reaction Force (GRF). The GRF is important external force acting upon the human body in motion. This force is used as propulsion to initiate and control the movement.
A single male weighing 74kg uninjured participant was subjected to an exercise to determine the ground reaction force. ...
the anterior-posterior component of GRF) versus time data and the braking and propulsive impulse were produced. From this raw data, we will need to obtain the magnitude of the following GRF related variables (shown in fig. 1) for each trial. Calculation of the changes in horizontal velocity during the braking phase, propulsive phase was done. An overall change in horizontal velocity during the stance phase is also analyzed.
The higher the velocity of the runner, the shorter the contact phase. The duration of the contact phase must of course be optimal, since the sprinter needs to develop the greatest possible horizontal force in the propulsive phase - this force namely pushes the runner forward. Biomechanics requires the acceleration phase of the stride to be the longest possible, so that the runner can develop maximal force. However, this duration is limited with the running velocity and some kinematic characteristics of the sprinting stride - especially the take-oft angle. Optimal execution of the contact phase causes a large difference between the impulses in the braking and the propulsive phases. The braking impulse should be the smallest possible, the propulsive impulse the greatest possible. Participant in the current study had an average duration of the contact phase. According to Bruggeman and Glad (1990), top runners that develop maximal velocity from 10.20 to 11.60 m.s-1 have a contact phase between 85 and 95 ms. The ratio between the duration of the braking phase and the propulsion phase was 40% : 60 %, which is from the viewpoint of economy a very good indicator of a rational technique of maximal sprinting velocity. The braking horizontal force and the braking time that define the braking impulse should be as small