The Correlation Between Muscle and Kinematic Synergies in Mono- and Multi-Planar Upper Limb Motions: A Study of Muscle-Joint Coordination

Abstract

An important issue in motor control is to investigate the functionality of muscle synergies in relation to the upper-limb joint kinematic characteristics. This study investigated the relationship between muscle and kinematic activation synergies in different upper limb functions. Electromyography data were recorded from 10 muscles, and kinematic data were tracked using 12 anatomical landmark points on the body to capture motion data from three healthy subjects during proprioceptive neuromuscular facilitation (PNF) patterns. These PNF patterns were considered multi-planar movements due to their involvement in motion across multiple anatomical planes, as well as basic motions. The inverse kinematic approach was used to obtain the joint angles from the marker positions by the musculoskeletal model. Half-wave rectification (HWR) was applied to divide each joint angle into two separate degrees of freedom (DOFs) in a positive direction. To involve more muscles in different types of motions, a verified musculoskeletal (MS) model, based on the results of computed muscle control (CMC) and processed electromyography data (EMG), was utilized to compute muscle activation. The non-negative matrix factorization (NNMF) approach was applied to extract kinematic and muscle synergies. Four synergies were extracted from both muscle and kinematic data based on the thresholds of 80% for local variance accounted for (VAF) and 95% for global VAF, respectively. Based on the similar activation trends and the correlation coefficients much more than 0.7 of the paired muscle and kinematic synergy patterns in the same order, each muscle synergy was associated with the corresponding kinematic synergy. Hence, the dominant muscles and the corresponding major DOFs in the paired muscle and kinematic synergies were recognized to illustrate the muscle recruitment of each to perform a phase of motion in the corresponding kinematic synergy.