The effects of precision demands during a low intensity pinching task on muscle activation and load sharing of the fingers.

High precision demands in manual tasks can be expected to cause more selective use of a part of the muscular synergy involved. To test this expectation, load sharing of the index finger and middle finger was investigated during a pinching task. Myoelectric activation of lower arm and neck-shoulder muscles was measured to see if overall level of effort was affected by precision demands. Ten healthy female subjects performed pinching tasks with three levels of force and three levels of precision demands. The force level did not significantly affect the relative contribution of the index and middle finger to the force. Higher precision demands, however, led to higher contribution of the index finger to the pinch force. Consequently, a more selective load of the forearm and hand occurs during tasks with high precision demands. The variability of the force contribution of the fingers increased during the task. No effects of precision demand on the activation of forearm and neck-shoulder muscles were found. Force level did affect the EMG parameters of several muscles. The effects were most apparent in the muscles responsible for the pinch force, the forearm muscles. Activation of these muscles was higher at higher force levels. In the trapezius muscle at the dominant side EMG amplitudes were lower at the high pinch force compared to the low force and median force conditions.