Analysis of surface EMG-force relation of the first dorsal interosseous muscle.

The electromyogram (EMG)-force relation was investigated using 2-dimensional surface electrode arrays. The surface EMG and isometric contraction forces were recorded from the first dorsal interosseous (FDI) muscles in 4 human subjects when they generated different levels of isometric contraction in three radial directions: abduction, flexion, and a linear combination of abduction and flexion. The surface EMG-force relation, fitted by a straight line, was constructed for each tested task direction. We found that the FDI muscle did not activate uniformly across the different directions of isometric contraction, resulting in variations in slope of the surface EMG-force relation. Furthermore, this variation was also sensitive to different channels of the surface electrode array on the muscle.