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The aims of this study were to quantify intrasegmental motion using an array of 28 surface-mounted markers to examine frequency and amplitude measurements of the intrasegmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One participant performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces, the muscle tension significantly affected the amount of intrasegmental motion. Tensing the arm reduced the intrasegmental motion by 50%. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intrasegmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70% of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intrasegment soft tissue motion can have on the kinetics of an impact.
M.T.G. Pain is with the School of Sport and Exercise Sciences, Loughborough University, Loughborough, LE11 3TU, U.K; J.H. Challis is with the Biomechanics Lab, Dept. of Kinesiology, The Pennsylvania State University, University Park, PA 16802-3408.