A surface electromyogram (EMG) was recorded from four leg muscles to measure the effects of various seat inclinations and an abduction orthosis on eight children with cerebral palsy and controls during performance of an upper-extremity task and while listening to a story. EMG responses were lowest in the forward-leaning and horizontal positions with the abduction orthosis, and highest in reclined and horizontal positions without the orthosis for both groups of children during the performance of an upper-extremity task. While listening to a story, there was no median EMG activity in any muscles of the controls, but there were wide variations in those of the children with cerebral palsy. The results indicate that the use of an abduction orthosis and horizontal and forward-leaning seats decrease lower-extremity muscle activity, and so it is possible that it might also improve upper-extremity function.