Development of simple camera-based system for lower limb alignment evaluation during cycling

Simple camera-based system for evaluation of lower limb alignment as a part of an automated cycling fitting system was developed and verified in this study. Developed imaging system can evaluate lower limb alignment quantitatively during pedaling using a general camcorder and single marker attached on the knee. Threshold-based marker detection algorithm with YCbCr color space was proposed in this study. Experiment was carried out to compare trajectory data from marker detection algorithm of the developed imaging system with trajectory data from 3-D motion analysis system. Result showed that average error between trajectories was 1.8 mm (0.57%) of range of motion (ROM) of 326 mm in the vertical direction and 2.3 mm (6.16%) of ROM of 37 mm in the medio-lateral direction. There existed significant correlation between two measured values (r=1.00 in the vertical direction and r = 0.926 in the medio-lateral direction). It can be concluded that developed imaging system be applied to evaluate lower limb alignment which is an important factor for bicycle fitting.