Muscle activation patterns in healthy subjects and stroke survivors in an unpredictable robotic environment

The purpose of this study was to describe muscle activity changes during learning of reaching movements in unpredictable dynamic environments. Healthy subjects and stroke survivors performed reaching tasks with a robotic manipulandum in a force field whose magnitude was randomised. In healthy subjects, electromyographic (EMG) activity of the biceps, triceps, anterior and posterior deltoid showed an effect of training on EMG onset time, peak onset time and integrated EMG. Differences in EMG tuning effects were also observed with training. In stroke survivors, only the biceps muscle showed reduction in EMG onset. Moreover, distinct target direction effects were noted. Differences in EMG tuning effects with training were conserved after stroke. In an unpredictable dynamic environment, healthy human subjects demonstrate motor adaptation by reducing their EMG onset times and stabilising the EMG directional effect of dynamic training. These characteristic effects are compromised albeit present in stroke survivors.