Three models of the vibrating ulna.

Abstract Three models were evaluated for prediction of ulnar resonant frequency given length, mineral content, and width. The ‘ulna’ was a homogeneous, isotropic cylindrical tube. For Model I, the tube was attached to rigid supports by hinges. For Model II, the tube was attached by springs. Model III was similar to Model II except for addition of a spring-mass system simulating an accelerometer strapped to the wrist. For all 3 models, the resonant frequency r.m.s. prediction error was ≤ 20 per cent relative to measured values in 118 schoolchildren. Models II and III were nearly independent of spring constant values: ± 50 per cent changes in these values changed resonant frequency by ≤ 1 per cent. Model III was nearly independent of accelerometer mass and interposed skin spring constant: Resonant frequency changed by ≤ 1 Hz over a range of 0–50 g and over a skin spring constant range of 1 5 -5 times the nominal value.