Soft tissue motion during impacts: their potential contributions to energy dissipation

The aims of this study were to quantify intra-segmental motion using an array of 28 surface mounted markers to examine frequency and amplitude measurements of the intra-segmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One subject 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 intra-segmental motion. Tensing the arm reduced the intra-segmental 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 intra-segmental 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 intra-segment soft tissue motion can have on the kinetics of an impact.