On skin movement artefact-resonant frequencies of skin markers attached to the leg

Abstract

In this paper, some dynamic effects of the relative motion between the skin and the underlying bone – skin movement artefact – are presented. Two parameters were investigated: (1) the local stiffness of different attachment sites along the leg and (2) the resonant frequencies of wand marker systems. The tangential stiffness was found to vary between 330 and 1900 N/m with the smallest stiffness found in the anterior/posterior direction on the proximal thigh. The highest stiffness measured was in the proximal–distal direction at the knee. The resonant frequencies of wand markers placed on the leg were found to be typically 23–51 Hz, depending on the mass of the marker. The effect of keeping the muscles tensed was also measured. Increased muscle tension provided a more stable base, producing increased stiffness.