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Between-dayreliability of three-dimensional motion analysis of the trunk: A comparison of marker based protocols


At a glance

  • Project leader : Fabian Rast
  • Project team : Christoph Bauer, Dr. Eveline Graf, Andre Meichtry
  • Project status : completed
  • Funding partner : Internal
  • Contact person : Christoph Bauer


Motion capture of the trunk using three-dimensional optoelectronic systems and skin markers placed on

anatomical 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 overdetermined

number of markers and optimization algorithms, or by defining the neutralposition using a reference

trial. The purpose of this study was to quantify and compare the between-day reliability of trunk

kinematics, when using these methods.

In each of two sessions, 20 subjects performed four movement tasks.Trunk kinematics were

established through the plug-in-gait protocol, the point cloud optimization algorithm, and by defining

upright standing as neutral position. Between-day reliability was analyzed using generalizability theory

and quantified by indexes of dependability.

Across all movement tasks, none of the methods was superior in terms of between-day reliability.The

point cloud algorithm did not improve between-day reliability,but did result in 24.3% greater axialrotation

angles.The definition of neutral position by means of a reference trial revealed 5.8% higher indexes of

dependability for lateral bending and axial rotation angles, but 13.7% smaller indexes of dependability for

flexion 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 angular

output are dependent on the movement task and the underlying research question.