Estimation of Trunk Inclination by Means of an Inclinometer

In an effort to estimate trunk inclination by means of a simple inclinometer, a theoretical model analysis was carried out to clarify the relation between "true" trunk inclination and the inclinometer reading. The effects of inclinometer location on the trunk, working posture, and weight handled were also investigated experimentally. The theoretical model was based on work by Anderson et al. to estimate pelvic rotation from trunk inclination. The theoretical results indicated that the relation between trunk inclination and the inclinometer reading would change according to the location of the inclinometer. The curves were concave, straight, and convex when the inclinometers were fixed on the trunk at low, intermediate, and high levels, respectively. In the experimental study, twelve male subjects held 1, 5, and 10 kg boxes at 0, 20, 40, and 60 cm from the floor in forward-bending and squatting postures. The inclinometers were fixed on the back at L4, Th12, and Th5. The relation between trunk inclination and the inclinometer reading in measurement data showed concave, straight, and convex curves at L4, Th12, and Th5, respectively, as the theoretical model analysis had indicated. At L4 and Th5, however, the relation could be regarded as linear because the coefficients of determinations (R^2 ) of the theoretical models calculated by the regression analyses agreed closely to those of the simple linear models. The difference between the forward-bending and squatting postures was large at L4, but small at Th12 and Th5. The effect of the weight handled was small and negligible in making these estimates.