Electromyographic study of the upper, middle and lower portion of the trapezius muscle in the circumduction movement of the arm on a shoulder wheel apparatus.

The upper, middle and lower portions of the trapezius muscle were analysed electromyographically (using a TECA TE-4 electromyograph and a single coaxial needle) in 20 healthy volunteers, during a circumduction movement of the arm, on a shoulder wheel apparatus. All three portions of the muscle were active, but the elevation phase of the arm was more pronounced in movements performed clockwise while the lowering phase was more manifest in movements performed counterclockwise. The position of the wheel gauntlet did not interfere significantly with the results.