Muscle co-contraction patterns in robot-mediated force field learning to guide specific muscle group training.

Background: Muscle co-contraction is a strategy of increasing movement accuracy and stability employed in dealing with force 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-mediated force field learning paradigm of motor adaptation.

Method: Forty-two participants volunteered to participate in a study utilising robot-mediated force field motor adaptation paradigm with a clockwise or counter-clockwise force field. Kinematics and surface electromyography (EMG) of eight arm muscles were measured.

Results: Both muscle activation and co-contraction was earlier and stronger in flexors in the 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.