ACCURACY ASSESSMENT OF METHODS FOR DETERMINING HIP MOVEMENT IN SEATEDCYCLING

The goal of this research was to examine the accuracy of three methods used to indicate the hip joint center (HJC) in seated steady-state cy cling. Two of the methods have been used in previous studies of cyclin g biomechanics and included tracking a marker placed over the superior aspect of the greater trochanter, a location that estimates the cente r of rotation of the hip joint, and assuming that the hip is fixed. Th e third method was new and utilized an anthropometric relationship to determine the hip joint location from a marker placed over the anterio r-superior iliac spine. To perform a comparative analysis of errors in herent in the three methods, a standard method which located the true hip joint center was developed. The standard method involved establish ing a pelvis-fixed coordinate system using a triad of video markers at tached to an intracortical pin. Three-dimensional motion analysis quan tified the true hip joint center position coordinates. To provide data for the comparative analysis, the intracortical pin was anchored to a single subject who pedaled at nine cadence-workrate combinations whil e data for all four methods were simultaneously recorded. At all caden ce-workrate combinations the new method was more accurate than the tro chanter method with movement errors lower by a factor of 2 in the vert ical direction and a factor of 3 in the horizontal direction. Relative to the errors introduced by the fixed hip assumption, the new method was also generally more accurate by at least a factor of 2 in the hori zontal direction and had comparable accuracy in the vertical direction . For computed kinetic quantities, the new method most accurately indi cated hip joint force power but the fixed hip method most accurately i ndicated the work produced by the hip joint force over the crank cycle .