determine the magnitue and direction of the anchoring force

The primary goal of these studies is to describe how muscles change shape and produce work (Blemker and Delp, 2005 Blemker et al., 2005 Lemos et al., 2005).

Muscle is a kinematically, geometrically, and materially complex tissue. The first is to directly model muscles using finite elements. In an effort to streamline the process, finite element analyses that include muscle-induced forces have taken one of two different modeling approaches. Very recently, comparative biologists have recognized the utility of FEA for predicting the behavior of complex systems and are beginning to use it to investigate the functional adaptations of living organisms (Korioth et al., 1992 Spears et al., 1993 Wootton et al., 2003 Witzel et al., 2004 Dumont et al., 2005 Metzger et al., 2005 Richmond et al., 2005 Strait et al., 2005) and to reconstruct the behaviors of extinct organisms (Richmond and Qin, 1996 Fastnacht et al., 2002 Preuschoft and Witzel, 2004 Rayfield, 2004, 2005).ĭespite advances driven by the biomedical industry (Teran et al., 2005), building three-dimensional finite element models of complex biological structures remains complicated and time consuming. As a predictive analysis tool, FEA has developed to the point where high technology companies now rely on it heavily to reduce or eliminate expensive and time-consuming prototype fabrication and testing (Ulrich and Eppinger, 2000). © 2007 Wiley-Liss, Inc.įinite element analysis (FEA) is a numerical tool that engineers use to investigate the behavior of physical systems such as engineered products and manufacturing processes. For these reasons, it is recommended that a mechanics-based method be adopted for determination of the proper traction loads to be applied to skeletal structures due to muscular activity. Consequently, it is difficult to predict spatially where the results of finite element analyses are likely to be compromised by using ad hoc muscle modeling methods. We also note that, due to the geometric complexity of many bone structures-such as the skull analyzed here-load transmission paths are difficult to conceptualize a priori. Although the methods are not validated by in vivo data, we submit that muscle-load modeling methods that account for the underlying physics of muscle wrapping on curved bone surfaces are likely to provide more realistic results than ad hoc approaches that do not.

Furthermore, our mechanics-based models required significantly less total applied muscle force to generate a bite-point reaction force identical to those produced by the ad hoc muscle loading models. While reasonable qualitative agreement was found in the states of stress of the skull between the four muscle load modeling methods, there were substantial quantitative differences predicted in the stress states in some high stressed regions of the skull. We modeled a highly complex skeletal structure, the skull of a Jamaican fruit bat ( Artibeus jamaicensis), to compare the four muscle-loading methods. A computer program was written to interface with a commercial finite element analysis tool to automatically apply traction loads to surface faces of elements in muscle attachment regions according to the various muscle modeling methods. These new models use a combination of tensile, tangential, and normal traction loads to account for muscle fibers wrapped around curved bone surfaces. This work introduces two mechanics-based approaches to modeling muscle forces exerted on curvilinear bone structures and compares the results with two traditional ad hoc methods of muscle loading.

Determine the magnitue and direction of the anchoring force