Musculoskeletal models must be scalable to sizes of different individuals to be useful for product design. This is very challenging, because scaling pertains not only to the overall geometry, but also to properties like muscle insertion points, muscle parameters and wrapping surfaces. A general method for scaling musculoskeletal models has been implemented into the AnyBody™ Respository models. The scaling procedure is implemented in a generic manner and allows the usage of user-defined scaling laws. For details on the theory behind please take a look at the scaling introduction presented by AnyBody™ researchers in cooperation with researchers from Ford: Abstract and Poster .
The models in the AnyBody™ Managed Model Repository have been made scalable by building generalized parameters into all the numbers in the model. Just about everywhere, numbers in the models have been replaced by calls to a scaling law. This means that all body models expect such a scaling law to be present, but it is up to the user to choose the actual law. This decoupling of the scaling laws from the body parts makes it possible for the user to choose between the laws that are supplied with the models or perhaps define a new law, without making any changes in the body models.
Currently there areseven scaling laws available in AnyBody™
- ScalingStandard (do not scale; i.e. use standard model size)
- ScalingUniform (scale equally in all directions; input is joint to joint distances)
- ScalingLengthMass (scale taking mass into account; input is joint to joint distances and mass)
- ScalingLengthMassFat (scale taking mass and fat into account; input is joint to joint distances)
- ScalingUniformExt (scale equally in all directions; input is external measurements)
- ScalingLengthMassExt (scale taking mass into account; input is external measurement)
- ScalingLengthMassFatExt (scale taking mass and fat into account; input is external measurements).
The parameters of the scaling laws are controlled by the mean of the AnyMan.any file. Several versions of this file are available the choice depending on the scaling strategy chosen. More details about how to use this file are given along the tutorial.
Please also notice that each scaling law scales the strength of the muscles, in addition to the size and mass of the bone. This strength scaling is done automatically in most cases. We will come back to it when needed. Users who need a more comprehensive introduction can view this recorded previous webcast entitled Anthropometrical Scaling of Musculoskeletal Models.
The first four scaling methods are covered in Lesson 1. They are often referred to as Joint to joint scaling methods. Lesson 2 covers the latter three which are based on external body measurement.
With the AnyBody™ Modeling System you already have a repository of models available, for details please see the AnyBody™ Assistant available from the menu. As a starting point for this tutorial please find the model StandingModelScalingDisplay. This model can be found in the folder Applications/Examples. This tutorial has been written using the AnyBody™ Managed Model Repository Ver. 1.1 (AMMRV1.1) if you see differences between the tutorial text and your own results please download AMMRV1.1 from http://forge.anyscript.org/gf/project/ammr/frs/
Now head on for Lesson 1: Joint to joint scaling methods.