Evaluation of muscular moment asymmetry using bilateral cyclograms

Abstract

Knowledge of bilateral asymmetry of moments of muscle forces is important because a “weak” muscle that is not fully ready to create the required moment can be identified and restored to provide symmetric gait. However, there is currently no method to determine the symmetry of muscular moments of the left and right sides of body during walking. Recently, new technique based on the geometric properties of symmetric diagrams, also called bilateral cyclograms, was introduced. In order to quantify the symmetry of muscular moments, a bilateral synchronized cyclogram which represents the same gait variables, i.e. moments, and two sides of the body was used. For symmetric gait, cyclogram should lie on a symmetry line passing through the origin inclined at an angle 45°. To study the gait variables, gait measurement was performed using a MoCap system (VICON MX; Oxford Metrics) and four force plates (AMTI, Advanced Mechanical Technology). Calculations of parameters of gait were performed using the OpenSim (NIH Center for Biomedical Computation). A three-dimensional lower extremity musculoskeletal model was used to estimate the moments of muscle forces of a subject during walking. The data from the OpenSim software were normalized, and then the bilateral cyclograms of two synchronized moments (of the left and right side of the body) are created and evaluated. The synchronized bilateral cyclograms of healthy subjects are considerably symmetrical in almost all cases (i.e. 86%). Shapes of the synchronized bilateral cyclograms of the moments of muscles of the subjects with cerebral palsy are significantly asymmetric in all cases. Based on the experiments, we found that the bilateral cyclograms can be used to study asymmetry of the moments of muscle forces. The technique could find applications in rehabilitation and clinical examinations.