Validity and reliability of triaxial accelerometers for inclinometry in posture analysis

There is a need for objective and quantitative methods for measuring postur e and movement, so that, for instance, exposure-response relationships for work-related musculoskeletal disorders can be established. Inclinometry dat a have been obtained from triaxial accelerometers based on uniaxial solid-s tate accelerometers used in conjunction with a computer program to perform co-ordinate transformations. The transducer can be mounted in an arbitrary orientation on a body segment, since if two reference positions are recorde d, the co-ordinate system of the transducer can be transformed to that of t he body segment. The angular error of the system is small (1.3 degrees), th e reproducibility is high (0.2 degrees), and the inherent angular noise is small (0.04 degrees) and independent of the orientation of the device. Unde r quasi-static conditions, the angular velocities can be derived from the i nclinometry data. The angular and the angular-velocity errors can be approx imated using the relative deviation of the acceleration magnitude from grav itation. For applications involving a high degree of movement, the accelero meter data are still valid, although they cannot be interpreted as inclinat ion. Used in combination with the computer program, the transducer can be u sed to measure posture and movement under static and quasi-static condition s, which occur in most areas of occupational work. It is shown that spheric al co-ordinates can be used to present the inclinometry data.