Between-dayreliability of three-dimensional motion analysis of the trunk: A comparison of marker based protocols
At a glance
Motion capture of the trunk using three-dimensional optoelectronic systems and skin markers placed onanatomical landmarks is prone to error due to marker placement, thus decreasing between-day relia-bility.The influence of these errors on angular output might be reduced by using an overdeterminednumber of markers and optimization algorithms, or by defining the neutralposition using a referencetrial. The purpose of this study was to quantify and compare the between-day reliability of trunkkinematics, when using these methods.In each of two sessions, 20 subjects performed four movement tasks.Trunk kinematics wereestablished through the plug-in-gait protocol, the point cloud optimization algorithm, and by definingupright standing as neutral position. Between-day reliability was analyzed using generalizability theoryand quantified by indexes of dependability.Across all movement tasks, none of the methods was superior in terms of between-day reliability.Thepoint cloud algorithm did not improve between-day reliability,but did result in 24.3% greater axialrotationangles.The definition of neutral position by means of a reference trial revealed 5.8% higher indexes ofdependability for lateral bending and axial rotation angles, but 13.7% smaller indexes of dependability forflexion angles. Further, using a reference trial resulted in 8.3° greater trunk flexion angles.Therefore, the selection of appropriate markerplacement and the corresponding calculation of angularoutput are dependent on the movement task and the underlying research question.