MUSCLE-ACTIVITY IS DIFFERENT FOR HUMANS PERFORMING STATIC TASKS WHICHREQUIRE FORCE CONTROL AND POSITION CONTROL

Muscle activation levels in humans were examined during two different static tasks which required the same joint angles and the same joint m oments. In the isometric case, joint angles were fixed and subjects we re required to match forces. In the isoinertial case, a constant load was imposed across the joint and the subject was required to match pos ition. It was observed that for a specified posture and for specified load conditions, EMG activity varied depending on whether the limb was loaded isometrically or isoinertially. That is, different co-activati on relationships were observed for position control versus force contr ol tasks during otherwise similar conditions. These results imply that the neural command for static tasks depends on more than joint angles and load magnitude.