The usefulness of adaptable multi-muscle co-activity measures in the trunk

Trunk co-activity can indicate coordination and stability. However, historical agonist-antagonist approaches to co-activity can over-simplify multi-planar, functional, and otherwise complex tasks. Here we present a flexible co-activity measure that expands the two-muscle case of co-activity to multiple muscles while attempting to retain the simplicity of agonist-antagonist co-activity. Computing instantaneous commonality and activity levels provides two dimensions of co-activity that can be combined into a single measure: phi. EMG data from functional movements and simulated automotive rear impacts were analysed with the currently proposed measure of co-activity in two- and multi-muscle cases. The ability to examine multiple muscles and incorporate multiple dimensions of co-activity can allow new insights into muscular coordination