Kinematic and Force Data Collection in Biomechanics by Means of Sonic Emitters—II: Force Data Collection and Application to the Human Shoulder Complex

In multisegmented mathematical models of the human body the most difficult and the least successful modeling of a major articulating joint has been the shoulder complex because of the lack of appropriate biomechanical data as well as the anatomical complexity of the region. In this paper, quantitative results on the variability of the stiffness of the shoulder complex dependent upon orientation of the upper arm are presented by applying the principles and theory developed in Part I. The paper starts with a descripition of a multiple-axis force and moment transducer and its utilization with sonic emitters in determining direction as well as location of the general force and moment vectors applied on a body segment. The numerical results which are presented for three subjects are in the form of plots showing the passive resistance of the shoulder complex as functions of drawer displacements of the upper arm along its long bone axis. Exponential and power curve fitting of the numerical results are also provided to establish intra-subject variations and similarities of the behavioral patterns of the axial stiffness characteristics of the human shoulder complex.