Fig. 2.

Schematic overview of the musculoskeletal models used. The 1-degree-of-freedom (1-DOF) model was driven by four Hill-type muscle-tendon models. The shoulder joint was fixed at 45° from the positive x-axis, and 0° elbow position was defined as fully stretched. For the simulations with the optimally controlled arm with combined spindle and Golgi tendon organ (GTO) feedback, the model was expanded to have 2 DOF (shoulder and elbow rotations) and 2 monoarticular shoulder muscles (depicted in red).