Effects of Sensor Types and Angular Velocity Computational Methods in Field Measurements of Occupational Upper Arm and Trunk Postures and Movements

Abstract

Accelerometer-based inclinometers have dominated kinematic measurements in previous field studies, while the use of inertial measurement units that additionally include gyroscopes is rapidly increasing. Recent laboratory studies suggest that these two sensor types and the two commonly used angular velocity computational methods may produce substantially different results. The aim of this study was, therefore, to evaluate the effects of sensor types and angular velocity computational methods on the measures of work postures and movements in a real occupational setting. Half-workday recordings of arm and trunk postures, and movements from 38 warehouse workers were compared using two sensor types: accelerometers versus accelerometers with gyroscopes—and using two angular velocity computational methods, i.e., inclination velocity versus generalized velocity. The results showed an overall small difference (<2° and value independent) for posture percentiles between the two sensor types, but substantial differences in movement percentiles both between the sensor types and between the angular computational methods. For example, the group mean of the 50th percentiles were for accelerometers: 71°/s (generalized velocity) and 33°/s (inclination velocity)—and for accelerometers with gyroscopes: 31°/s (generalized velocity) and 16°/s (inclination velocity). The significant effects of sensor types and angular computational methods on angular velocity measures in field work are important in inter-study comparisons and in comparisons to recommended threshold limit values.

Evaluation of a New Simplified Inertial Sensor Method against Electrogoniometer for Measuring Wrist Motion in Occupational Studies

“…However, most multi-sensor systems are complex to use in the field by practitioners [18,19]. In addition, many systems can be used for assessments of the upper arm and trunk, but few can be used for assessment of wrist motion [20][21][22]. Recent research has explored a multi-sensor system focusing on wrist risk assessment.…”

Concerning a Work Movement Velocity Action Level Proposed in “Action Levels for the Prevention of Work-Related Musculoskeletal Disorders in the Neck and Upper Extremities: A Proposal” by Inger Arvidsson et al. (2021)

“…To find what the 60°/s action level of Arvidsson et al (2021) corresponds to in the other three velocity distributions, we used the four velocity distributions of each worker and computed the corresponding action levels. The generalized velocity of 60°/s, with accelerometers only, corresponded to the inclination velocity of 27°/s from accelerometers only, to 26°/s in generalized velocity of from accelerometers with gyroscopes and to the inclination velocity of 13°/s from accelerometers with gyroscopes ( Fan et al , 2021 ). These values are obtained from a field study including one occupational group.…”

“…We recently performed a study ( Fan et al , 2021 ), where we investigated the effect of sensor type, i.e. accelerometers versus IMUs, and the effect of computational arm velocity method, i.e., inclination versus generalized angular velocity, on postures and movements of the arm and trunk.…”

“…To conclude, while posture percentiles may be compared, it is clear that upper arm velocities depend greatly on sensor types and on chosen computational method, and that the recommended action level by Arvidsson et al (2021) need to be transformed, with above given corresponding velocities or with at the time more recent ones, before being applied to measurements from IMUs and/or for inclination velocities, which have been used in several recent studies (see Fan et al , 2021 ).…”

Reply to Letter to the Editor, by Mikael Forsman, Xuelong Fan, Ida-Märta Rhen and Carl Mikael Lind

“…Due to historical technical limitations, using accelerometers only since gyroscopes were not available, we have defined generalized angular velocity according to Hansson et al (2001) . The generalized angular velocity obtained by gyroscopes + accelerometers (IMUs) is more correct, as indicated by Fan et al (2021) . Despite knowing this, we have kept the same method in order to build a database over time.…”