High resolution determination of body segment inertial parameters and their variation due to soft tissue motion

This study had two purposes: to evaluate a new method for measuring segment al dimensions for determining body segment inertial parameters (BSIP), and to evaluate the changes in mass distribution within a limb as a consequence of muscular contraction. BSIP were calculated by obtaining surface data po ints of the body under investigation using a sonic digitizer, interpolating them into a regular grid, and then using Green's theorem which relates sur face to volume integrals. Four skilled operators measured a test object; th e error was approximately 2.5%, and repeatability was 1.4% (coefficient of variation) in the determination of BSIP. Six operators took repeat measures on human lower legs; coefficients of variation were typically around 5%, a nd 3% for the more skilled operators. Location of the center of mass of the lower leg was found to move up 1.7 cm proximally when the triceps surae. m uscles went from a relaxed state to causing plantar flexion. The force duri ng an impact associated with such motion of the soft tissue of the lower le g was estimated to be up to 300 N. In summary, a new repeatable and accurat e method for determining BSIP has been developed, and has been used to eval uate body segment mass redistribution due to muscular contraction.