Motion analysis without any device

It is possible to carry out motion analysis without any device, although these methods are not reliable. It is suggested that 2D recordings about motions should be done from appropriate distance (see: video recording). Parallel to the direction of motions a horizontal object must be placed. It helps to define “x” axis as recordings do not contain frame of reference. A “fix” point should be shown which is under and behind the analyzed motion.  The origin of the coordinate system should be assigned. While recording the axis must be drown so that it will be parallel to the direction/orientation of the horizontal object. The “y” axis should be drawn horizontal starting form a ‘fix’ point behind the motion. The drawing of the axes is done with the help of anthropometry (it is a science that defines physical measures of individuals). Size and forms of a body can be measured precisely with these methods. Subsequent calculations will be easier if joints are marked. The longitudinal axis of a part of a body should be lengthen so that it will intersect “x” axis, thus angles can be measured. Getting these data the size and extent of horizontal projection of “x” and “y” axes can be defined with mathematical formulas:

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By using this method the parts/segments of a body and joints on the test plane can be defined and calculated. Further data and calculations are needed to define the centre of gravity of body segments. The body is divided up into segments which are located/defined by joint axes of rotation. The percentage calculations of centre of gravity of these body segments were described by Demster (1955), see table 1. The basis of calculations was distal and proximal epiphysis of body segments. Alignment of more segments can be considered bigger ones (upper arm, forearm, hand). If the torso is not straight then it must be divided up into chest (T1: Th. 1-12), abdomen (T2: L. 1-4) and pelvis (T3) (Barton and Szende, 1981). Their centre of gravity is on the midpoint of symmetry axis. For the definition of the centre of gravity of a whole body it is crucial to use the weight ratio of segments correlating to the whole weight ratio (Dempster, 1955, table 1.). As soon as the centre of gravity of segments has been drawn in a coordinate system (in case of limbs right and left limbs are separated) the centre of gravity of a body can be defined. The coordinates of the centre of gravity of segments (“x” and “y”) should be multiplied with their weight ratio and the sum of these will give the coordinates (x, y) of the centre of gravity of a body (see table 2). For the measurement of velocity and acceleration more recordings should be done. If the speed of recordings is known the velocity of a motion  can be calculated from the quotient of the distance travelled between the two images (…képlet) in a given period of time (…képlet). The speed change (képlet) between two images in a given time will serve information about acceleration. To be able to calculate angular velocity () the changes of angular (…képlet) between the longitudinal axis of the same two body segments and the elapsed time (…képlet) must be used (…képlet). The angular velocity (…képlet) can be calculated from the data of angle change (…képlet) between images and from the elapsed time (…képlet). The momentary magnitude of force (…képlet) can also be calculated from the product of mass and momentary acceleration (…képlet).