The aim of this study was to investigate the effect of errors in the location of the center of pressure (5 and 10 mm) on lower limb joint moment uncertainties at different gait velocities (1.0, 1.5, and 2.0 m/s). Our hypotheses were that the absolute joint moment uncertainties would be gradually reduced from distal to proximal joints and from higher to lower velocities. Joint moments of five healthy young adults were calculated by inverse dynamics using the bottom-up approach, depending on which estimate the uncertainty propagated. Results indicated that there is a linear relationship between errors in center of pressure and joint moment uncertainties. The absolute moment peak uncertainties expressed on the anatomic reference frames decreased from distal to proximal joints, confirming our first hypothesis, except for the abduction moments. There was an increase in moment uncertainty (up to 0.04 N m/kg for the 10 mm error in the center of pressure) from the lower to higher gait velocity, confirming our second hypothesis, although, once again, not for hip or knee abduction. Finally, depending on the plane of movement and the joint, relative uncertainties experienced variation (between 5 and 31%), and the knee joint moments were the most affected.
Franklin Camargo-Junior is with the Department of Physical Therapy, Speech and Occupational Therapy, School of Medicine, University of São Paulo, Sao Paulo, Brazil. Marko Ackermann is with the Department of Mechanical Engineering, Centro Universitário da FEI, Sao Paulo, Brazil. Jefferson F. Loss is with School of Physical Education, Federal University of Rio Grande do Sul, Rio Grande do Sul, Brazil. Isabel C.N. Sacco (Corresponding Author) is with the Department of Physical Therapy, Speech and Occupational Therapy, School of Medicine, University of São Paulo, Sao Paulo, Brazil.