Introduction to Scaling

Musculoskeletal models must be scalable to sizes of different individuals to be useful for product design. Scaling pertains not only to the overall geometry, but also muscle insertion points, muscle parameters, wrapping surfaces etc. AnyBody has a both generic and user-define scaling laws for models in the repository.

For details on scaling theory behind please take a look at Rasmussen 2005.

Size related parameters of models in the AMMR are seldom defined as constant numbers, but instead computed from global measurements (e.g., total height, weight of human) based on a scaling law. Thus all body models expect the definition of a scaling law, although user can choose the actual law.

Currently there are nine pre-defined scaling laws available in AnyBody

Scaling

Scaling laws
Scaling law Description
ScalingStandard scale to a standard size; i.e. use 50th percentile sizes for a European male
ScalingNone do not scale; i.e. use underlying cadaveric dataset as is
ScalingUniform cale segments 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.
ScalingXYZ scale taking mass and fat into account; scale segments along X, Y, Z axes; input is scale factors along X, Y, Z axes.

Input parameters of scaling laws are specified in a file that is always named AnyMan.any. Several versions of this file are available, each for a different scaling law. More details can be found the in the tutorial below.

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 titled “Anthropometrical Scaling of Musculoskeletal Models”.

Tutorial

The first five scaling methods are covered in Lesson 1. They are often referred to as Joint to joint scaling methods. Lesson 2 covers the next three which are based on external body measurement. And Lesson 3 covers the ScalingXYZ scaling law, since the usage logic slightly differs from the rest of the laws.

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.

See also

Next lesson: Now head for Lesson 1: Joint to Joint Scaling Methods.