Force Plate Analysis - Lab Report Example

Biomechanics Lab Report Force Plate Analysis Introduction A kistler force plate was used to measure the horizontal velo of the braking phase, propulsive phase and the stance phase. Using the motion analysis data along with ground reaction force the joint moments are calculated. The Kistler Force Plates use triaxial piezoelectric force transducers mounted at the corners of each plate to measure the three components of the ground reaction force vector (vertical, anterior-posteror, and medio-lateral) throughout the stance phase of gait.. For comparing data between different subjects and/or sessions, the joint moments are normalized to body weight. The change in the horizontal velocity during the braking, propulsive and stance phase are calculated. In the results the changes are summarized and the variables are presented in relation to the body weight of the individual rather than in Newtons. 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. Method A single male weighing 74kg uninjured participant was subjected to an exercise to determine the ground reaction force. Following habituation, GRF was recorded while he was running across the Kistler Force Plate five times at 3, 4 and 5 m-s-1 10% . Following each trial during the laboratory session, a MS-Excel spreadsheet containing Fz (i.e the vertical component of GRF) and the Fy (i.e. 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. Results 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 as possible so that there is the least possible drop in horizontal velocity of CC in the first part of the contact phase. In the current study, the average horizontal velocity decreased for 1.4 % in the braking phase, showing a very economical execution of the sprinting stride. Previous research on sprinters (Mero, komi & Gregor, 1992) has reported drops in velocity in the braking phase between 3.1 and 4.8 %. Discussion The ground reaction force has three components: X-, Y- and Z-components. Among these, the Y-component is along the direction of the motion which reflects the propulsion or the braking force. The Z-component is used to support the body so that to prevent the body from collapsing, and also to thrust the body upward in jumping motion. There are two peaks in the vertical ground reaction force. The first peak is called the impact peak (P1) while the second is called the propulsion peak (P2). The impact peak is associated with the impact of the foot to the ground during early foot contact phase. The propulsion peak is associated with the propulsion of the body forward. It has always been the main focus of the shoe engineers that how to design the shoe-sole to reduce the impact peak while maintaining the propulsive characteristics. The max. vertical ground reaction force in jogging reaches 2 to 3 times the body weight. The factors affecting the magnitude of the ground reaction force are running style (rearfoot, midfoot or forefoot strike), running speed, footwear, ground surface, inclination of the ground, etc. The time periods involved in ground reaction force development are also very important since these determine the rate of impact or force development. Conclusion The study aims to investigate the effect of increasing running speed on ground reaction force. The result shows that the contact phase should be as short as possible and realised in such a way that there is the least possible reduction in the horizontal velocity of CG in the braking phase, An economic execution of the braking phase depends mostly on the grabbing velocity of the thigh and the foot just before touchdown. In light of this, training should be oriented into developing quick and reactive power and practising the technique of movement with the swing leg in the front support phase. A high grabbing velocity of the swing leg has, as a consequence, a higher stride rate that directly affects the result in sprinting. The function of the shank muscles is especially important. Their electrical activation begins before touchdown. Necessary stiffness of the muscles that must resist the force of the surface in the forward support phase is ensured in this way. It is therefore concluded that the increase in running speed will decreased the ground reaction force depending on the variables involved. Reference: Ground Reaction Force http://www.bsu.edu/web/ykwon/pep294/lab8/grf_lab.html Read More