The kinematic foundation (Holzbaur et al. 2005 (link)) for the dynamic model included 15 degrees of freedom at the glenohumeral joint (including movement of the clavicle and scapula (de Groot & Brand 2001 )), elbow, forearm, wrist, thumb and index finger, with conventions as recommended by the International Society of Biomechanics (Wu et al. 2005 (link)). For these dynamic simulations, we reduced the degrees of freedom to 7 in both platforms; 8 degrees of freedom were eliminated by positioning the hand in a grip posture and fixing the degrees of freedom at the index finger and thumb (Fig. 1 ).
Joint kinematics were defined identically in both platforms with the exception of wrist flexion. As indicated by experimental data (Ruby et al. 1988 (link)), wrist flexion in both models is distributed evenly across the proximal and distal rows of carpal bones. In OpenSim, the generalized coordinate wrist flexion directly specifies the rotation of both carpal rows, (e.g., 1° of wrist flexion specifies a 0.5° rotation about the proximal row and a 0.5° rotation about the distal row). In SIMM-SD/Fast, a coordinate transformation was needed because SD/Fast requires a 1:1 correspondence between the generalized coordinate and the imposed rotation. Thus, the generalized coordinate proximal flexion is used, where, such that 1° of proximal flexion specifies a 1° rotation about the proximal row and a 1° rotation about the distal row, and is identical to 2° of wrist flexion. Despite the coordinate transformation, both platforms have equivalent wrist kinematics. Given (1), the magnitude of proximal flexion moment is equal to twice the magnitude of the corresponding wrist flexion moment. For consistency, we have transformed proximal flexion to wrist flexion for presentation of results throughout the study.
In this study, we added inertial parameter definitions for the segments in the model. Inertial properties were defined for the hand, radius, ulna, and humerus based on previously published descriptions for these segments (McConville et al. 1980 , Reich & Daunicht 2000 (link)). The masses of the clavicle and scapula were each obtained from (Blana et al. 2008 (link)), as derived from (Clauser et al. 1969 ). We determined the mass center and inertia tensor for clavicle and scapula from the geometric properties of polygonal bone descriptions in the model, with the anthropometry of a 50th percentile male (Gordon et al. 1989 ) (SolidWorks Professional, Dassault Systèmes SolidWorks Corp., Waltham, Massachusetts). Inertial properties were implemented identically in both platforms (Table 1 ).
Joint kinematics were defined identically in both platforms with the exception of wrist flexion. As indicated by experimental data (Ruby et al. 1988 (link)), wrist flexion in both models is distributed evenly across the proximal and distal rows of carpal bones. In OpenSim, the generalized coordinate wrist flexion directly specifies the rotation of both carpal rows, (e.g., 1° of wrist flexion specifies a 0.5° rotation about the proximal row and a 0.5° rotation about the distal row). In SIMM-SD/Fast, a coordinate transformation was needed because SD/Fast requires a 1:1 correspondence between the generalized coordinate and the imposed rotation. Thus, the generalized coordinate proximal flexion is used, where, such that 1° of proximal flexion specifies a 1° rotation about the proximal row and a 1° rotation about the distal row, and is identical to 2° of wrist flexion. Despite the coordinate transformation, both platforms have equivalent wrist kinematics. Given (1), the magnitude of proximal flexion moment is equal to twice the magnitude of the corresponding wrist flexion moment. For consistency, we have transformed proximal flexion to wrist flexion for presentation of results throughout the study.
In this study, we added inertial parameter definitions for the segments in the model. Inertial properties were defined for the hand, radius, ulna, and humerus based on previously published descriptions for these segments (McConville et al. 1980 , Reich & Daunicht 2000 (link)). The masses of the clavicle and scapula were each obtained from (Blana et al. 2008 (link)), as derived from (Clauser et al. 1969 ). We determined the mass center and inertia tensor for clavicle and scapula from the geometric properties of polygonal bone descriptions in the model, with the anthropometry of a 50th percentile male (Gordon et al. 1989 ) (SolidWorks Professional, Dassault Systèmes SolidWorks Corp., Waltham, Massachusetts). Inertial properties were implemented identically in both platforms (