Muscle activation patterns during force generation of the index finger.

The article investigated whether joint postures affect index finger muscle activation patterns. Ten subjects attempted to produce submaximal isometric forces in six orthogonal directions (palmar, dorsal, abduction, adduction, distal and proximal) at each of 9 different joint postures. Activation patterns were recorded from intramuscular electrodes inserted into 6 of the index finger muscles. Post hoc statistical analysis revealed that joint angles significantly affected muscle activation levels for each of the force directions. Activation was especially sensitive to interphalangeal joint angles; changes in these angles led to not only changes in the magnitude of activation but to changes in patterns as well.