Inertia of a Human

Introduction

We often model the human body as collection of rigid bodies connected by flexible joints, potentially passive or active. The measurement of the physical properties (mass, center of mass and inertia) of a human is difficult because the human body parts are not as easily described as rigid bodes with defined joints and inflexible geometry, daily varying mass, wobbly mass, etc. Human mass, center of mass and inertia properties have been measured and estimated in a multitude of ways. Each method has its advantages and disadvantages.

• Cadaver measurements: [Dempster1955], [Clauser1969], [Chandler1975] 
• Photogrammetry: [Jensen1978]
• Ray scanning techniques: [Zatsiorsky1983], [Zatsiorsky1990]
• MRI: [Pearsall1994], [Cheng2000]
• Water displacement [Park1999] 
• Geometrical estimation [Yeadon1990a]

Bjørnstrup, J. 1995 gives a nice overview of most of these methods.

Yeadon Method

Yeadon’s geometrical estimation works well for the types of studies we do and allows us to quickly generate inertial properties from various people and supports a large range of configurations. We’ve written a software package called yeadon that automates the process.

Whipple Bicycle Model with Yeadon inertia

The yeadon package can be paired with various models, in particular the Whipple bicycle model. We’ve developed a software package that configurations an arbitrary rider to sit on an arbitrary bicycle. Various parameter sets can be extracted from the model for different rider bio-mechanical models.