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Internal Validity of the Functional Method of Hip Joint Center Location
Young-Hoo Kwon,Gary A. Christopher,Suk-Hoon Yoon 한국체육학회 2007 International journal of human movement science Vol.1 No.2
The internal validity of a new brace-based multi-marker protocol was assessed using a set of self-validation measures and different marker strategies and algorithms were compared to gain insights into the behavior of the functional method. Eighteen female volunteers participated in this study; each performed three trials of a flexionextension- abduction-adduction movement sequence. All trials were performed with the right knee fixed in extension by a full-length knee brace to enforce the rigidity of the leg and to minimize the skin movement artifacts. Reflective markers were placed on the brace (five leg markers), sacrum, and right and left ASIS’. The HJC position was computed using two algorithms, Downhill Simplex and Gamage-Lasenby, representing two different object function families. Two groups of marker strategies were also used: single marker (INDIVIDUAL) and multi-marker (MEAN, CENTROID, and ENSEMBLE). Four self-validation measures were developed: Rigidity Index (RI), Sphericity Index (SI), and intra- and inter-trial Consistency Indices (CI). The mean RI and SI values were significantly smaller than the mean reconstruction error of the camera calibration, confirming the internal validity of the brace-based multi-marker protocol. The new protocol also exhibited good intra-trial and inter-trial consistency of the HJC coordinates. The multimarker strategies provided more consistent results than the INDIVIDUAL strategy, and the ENSEMBLE strategy provided significantly smaller SI and inter-trial CI values than other strategies. Both algorithms generated similar results showing no superiority to one another.