The purpose of the study is to explore the feasibility of using a wearable device, called a myoelectric-computer interface (MCI), to improve arm movement in people who have had a stroke. Impaired arm movement after stroke is caused not just by weakness, but also by impaired coordination between joints due to abnormal co-activation of muscles. These abnormal co-activation patterns are thought to be due to abnormal movement planning.The MCI aims to reduce abnormal co-activation by providing feedback about individual muscle activations. This randomized, controlled, blinded study will test the home use of an MCI in chronic and acute stroke survivors.