On skin movement artefact-resonant frequencies of skin markers attached tothe leg

In this paper, some dynamic effects of the relative motion between the skin and the underlying bone - skin movement artefact - are presented. Two para meters were investigated: (1) the local stiffness of different attachment s ites 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 t he smallest stiffness found in the anterior/posterior direction on the prox imal thigh. The highest stiffness measured was in the proximal-distal direc tion at the knee. The resonant frequencies of wand markers placed on the le g 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 musc le tension provided a more stable base, producing increased stiffness. (C) 1999 Elsevier Science B.V. All rights reserved. PsycINFO classification: 22 60.