Fig 2. Recordings from one subject.

Mean angular velocity and acceleration of shoulder flexion, mean reactive torque on the trunk at shoulder height, and mean normalized EMG in % of that at maximum voluntary contraction of the four different trunk muscles for three repetitions of a medium sized arm movement. The dashed line indicates mean onset of deltoid EMG and the shaded areas illustrate the two intervals of EMG amplitude measurements. The solid vertical lines indicate: 1 = start of acceleration of shoulder flexion, 2 = start of deceleration of shoulder flexion and 3 = end of shoulder flexion. Note the two peaks of activation in TrA corresponding to both acceleration and deceleration of the arm movement.