Hysteresis cycle during arm abduction and adduction in static positions

Electromyography of the scapular waist muscles-in particular, the deltoid medium-showed a behavior resembling a hysteresis loop when the signal amplitude was plotted as a function of the arm position. Such loop was repeated in all the candidates who performed the test. It probably manifests the contribution of other regional muscles, as they enter into action or cease to contract, during the abduction-adduction maneuver. The phenomenon deserves further analysis