Muscle co-contraction patterns in robot-mediated force field learningto guide specific muscle group training

BACKGROUND: Muscle co-contraction is a strategy of increasing movement accuracy and stability employed in dealing with perturbation of movement. It is often seen in neuropathological populations. The direction of movement influences the pattern of co-contraction, but not all movements are easily achievable for populations with motor deficits. Manipulating the direction of the force instead, may be a promising rehabilitation protocol to train movement with use of a co-contraction reduction strategy. Force field learning paradigms provide a well described procedure to evoke and test muscle co-contraction. OBJECTIVE: The aim of this study was to test the muscle co-contraction pattern in a wide range of arm muscles in different force-field directions utilising a robot-assisted force field learning paradigm of motor adaptation. METHOD: 42 participants volunteered to participate in a study utilising robot-assisted motor adaptation paradigm with clockwise or counter-clockwise force field. Kinematics and surface electromyography (EMG) of eight arm muscles has been measured. RESULTS: Both muscle activation and co-contraction was earlier and stronger in flexors in clockwise condition and in extensors in the counter-clockwise condition. CONCLUSIONS: Manipulating the force field direction leads to changes in the pattern of muscle co-contraction