Visualization of trunk muscle synergies during sitting perturbations using self-organized maps
May 19, 2012
The purpose of this study is to utilize and demonstrate the use of the self-organizing map (SOM) method for visualization, modelling and comparison of trunk neuromuscular synergies during sitting. Thirteen participants were perturbed at the level of the sternum, in eight directions during sitting. Electromyographic (EMG) responses of ten trunk muscles involved in postural control were recorded. The SOM was used to encode the EMG responses on a two-dimensional (2-D) projection (i.e., visualization). The result contains similar patterns mapped close together on the plot therefore forming clusters of data. Such visualization of ten EMG responses following eight directional perturbations allows comparisons of direction-dependent postural synergies. Direction-dependent neuromuscular response models for each muscle was then constructed from the SOM visualization. The results demonstrate that SOM was able to encode complex neuromuscular responses and the visualization shows direction-dependent differences in the postural synergies. Moreover, each muscle was modelled using the SOM-based method and shows that all muscles, except one, produce a Gaussian fit for direction-dependent responses which is supported in the literature. Overall, SOM analysis offers a reverse engineering method for exploration and comparison of complex neuromuscular systems, which can describe postural synergies at a glance.
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