Optical motion capture
The accepted standard for joint angle estimation is optical motion capture (OMC). OMC works by using infra-red (IR) cameras to locate IR-reflective markers in 3D space. Markers are placed on specific anatomical landmarks (e.g., anterior-superior iliac spines, femoral epicondyles, etc.) which allow the reconstruction of segment frames. The relative orientation of adjacent frames is then used to compute the joint angles of interest [10]. OMC suffers from several limitations including a finite capture volume, high cost, setup complexity, and the need for little or tight-fitting clothing to prevent marker occlusion. These limitations prevent the broad use of OMC outside of research institutions and limit the types of activities that can be observed. Nevertheless, OMC remains the gold standard research method for capturing human movement, and especially joint angles. However, shortcomings of OMC have motivated the development of alternative methods for measuring joint kinematics. With the recent advances in micro-electromechanical systems (MEMS), inertial measurement units (IMUs) are being utilized with increasing frequency in biomechanics to estimate joint angles [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28].
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