Fig. 11.

Predicted torque direction vectors for anterior deltoid (AD, top) and the sternocostal head of pectoralis major (SPec, bottom), viewed in the body-fixed frame of reference. Vectors from 28 different arm postures are shown, representing three values each of upper arm azimuth, elevation, and humeral rotation and one additional posture. For the 27 postures, η ranged from −15 to −75°, θ ranged from 15 to 75°, and ζ ranged from −15 to 75°. Also included in each panel is a vector representing upper arm vertical (the 28th vector). Vectors are colored for upper arm elevation (θ), withyellow vectors representing 0 or 15°,orange representing 45°, and redrepresenting 75°. All vectors originate at the right shoulder of a mannequin, and the mannequins faceforward. The M_x′-axis also points forward, the−M_y′-axis points to the leftof the page (the mannequins’ right), and theM_z′-axis points upward.