In vitro simulation of 3D shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: 1) robotically simulate 7 healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in 6 cadavers, 2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics and 3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5° were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3° mean absolute error was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over 5 repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform...(truncated to fit word count, missing text in main PDF includes R2 changes).