Three-dimensional modelling of the motion range of axial rotation of the upper arm.

Computer simulation of human movements and postures suffers generally from the lack of reliable data, such as data on joint limits. In this paper, the motion range of axial rotation of the upper arm was investigated. An original surface regression fitting method using an orthogonal homogeneous polynomial basis has been presented. The method was used to fit both maximum internal and external upper arm axial rotation surfaces based on the experimental data from seven male subjects of ages 23-34. Under the assumption of normal distribution, the sample mean and the confidence limits for population mean of both internal and external upper arm axial rotation limits were derived. It has been shown that the axial motion range of the upper arm depends strongly on the position of the upper arm in the shoulder sinus cone and varies on average from 94 to 157 degrees. The present work can be considered as an extension of the shoulder kinematic data base established by Engin and Chen (1986), Journal of Biomechanical Engineering 108, 215-221.