A new method for gravity correction of dynamometer data and determining passive elastic moments at the joint.
Anderson-DE; Nussbaum-MA; Madigan-ML
J Biomech 2010 Apr; 43(6):1220-1223
Moments measured by a dynamometer in biomechanics testing often include the gravitational moment and the passive elastic moment in addition to the moment caused by muscle contraction. Gravitational moments result from the weight of body segments and dynamometer attachment, whereas passive elastic moments are caused by the passive elastic deformation of tissues crossing the joint being assessed. Gravitational moments are a major potential source of error in dynamometer measurements and must be corrected for, a procedure often called gravity correction. While several approaches to gravity correction have been presented in the literature, they generally assume that the gravitational moment can be adequately modeled as a simple sine or cosine function. With this approach, a single passive data point may be used to specify the model, assuming that passive elastic moments are negligible at that point. A new method is presented here for the gravity correction of dynamometer data. Gravitational moment is represented using a generalized sinusoid, which is fit to passive data obtained over the entire joint range of motion. The model also explicitly accounts for the presence of passive elastic moments. The model was tested for cases of hip flexion-extension, knee flexion-extension, and ankle plantar flexion-dorsiflexion, and provided good fits in all cases.
Biological-systems; Biomechanical-modeling; Biomechanics; Ergonomics; Humans; Mathematical-models; Muscle-function; Musculoskeletal-system; Posture;
Author Keywords: Isokinetic dynamometer; Joint moment; Gravity correction; Gravitational moment; Passive elastic moment
Michael L. Madigan, Department of Engineering Science and Mechanics, Virginia Tech-Wake Forest School of Biomedical Engineering and Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 20461
Journal of Biomechanics
Virginia Polytechnic Institute and State University