Inertial measurement units (IMU) are gaining increasing importance for human motion tracking in a large variety of applications. IMUs consist of gyroscopes, accelerometers, and magnetometers which provide angular rate, acceleration, and magnetic field information, respectively. In scenarios with a permanently distorted magnetic field, orientation estimation algorithms revert to using only angular rate and acceleration information. The result is an increasing drift error of the heading information. This article describes a method to compensate the orientation drift of IMUs using angular rate and acceleration readings in a quaternion-based algorithm. Zero points (ZP) were introduced, which provide additional heading and gyroscope bias information and were combined with bidirectional orientation computation. The necessary frequency of ZPs to achieve an acceptable error level is derived in this article. In a laboratory environment the method and the effect of varying interval length between ZPs was evaluated. Eight subjects were equipped with seven IMUs at trunk, head and upper extremities. They performed a predefined course of box handling for 40 min at different motion speeds and ranges of motion. The orientation estimation was compared to an optical motion tracking system. The resulting mean root mean squared error (RMSE) of all measurements ranged from 1.7 deg to 7.6 deg (roll and pitch) and from 3.5 deg to 15.0 deg (heading) depending on the measured segment, at a mean interval-length of 1.1 min between two ZPs without magnetometer usage. The 95% limits of agreement (LOA) ranged in best case from −2.9 deg to 3.6 deg at the hip roll angle and in worst case from −19.3 deg to 18.9 deg at the forearm heading angle. This study demonstrates that combining ZPs and bidirectional computation can reduce orientation error of IMUs in environments with magnetic field distortion.

The examination of joint range of motion (RoM) is part of musculo-skeletal functional diagnostics, used, for example, in occupational examinations. Various examination methodologies exist that have been optimized for occupational medical practice, which means they were reduced to the most necessary and feasible measures and examinations for efficiency and usability reasons. Because of time constraints in medical examinations in occupational settings, visual inspection is commonly used to quantify joint RoM. To support medical examiners, an inertial sensor-based measurement system (CUELA) was adapted for joint RoM examination in these settings. The objective of the present study was to evaluate the measurement tool in functional diagnostics under conditions close to clinical practice. The joint RoM of twenty healthy subjects were examined by three physicians, who were simultaneously using the measurement tool. Physicians were blinded to the measurement results and the other physicians. Active RoM was examined on the cervical, thoracic and lumbar spine while passive RoM was examined on the shoulder, elbow, wrist, hip, and knee, resulting in a total of 40 joint examination angles. The means, standard deviations, intraclass correlation coefficients (I C C 3,k ), and Bland-Altman-Plots were calculated using MatLab for statistical analysis. Most measurement results were in accordance with expected joint RoMs. All examinations showed an acceptable repeatability. In active RoM examinations, the ICC of inter-rater reliability varied between 0.79 and 0.95. In passive RoM examination the ICC varied between 0.71 and 0.96, except examination angles at the elbow and knee extension (ICC: 0.0-0.77). The reliability and objectivity of active RoM examinations were improved by the measurement tool compared with examiners. In passive RoM examinations of upper and lower extremities, the increase of objectivity by the measurements was limited for some examination angles by external factors such as the individual examiner impact on motion execution or the given joint examination conditions. Especially the elbow joint examination requires further development to achieve acceptable reliability. A modification in the examination method to reduce the examiner impact on measurement and the implementation of a more complex calibration procedure could improve the objectivity and reliability of the measurement tool in passive joint RoM examination to be applicable on nearly the whole body.

The usage of smart glasses in goods logistics and order picking has mainly been studied through cross-sectional experimental studies. Our longitudinal field study investigated the effects of smart glasses on the eyesight of 43 employees at two German companies. We combined ophthalmological examinations and questionnaire surveys at two points in time, six months apart. The vision of the employees was examined before and after each work shift. Mixed effects logistic regression was conducted to determine the associations between smart glasses use and effects on visual acuity. In the baseline examination, differences in eyesight before and after shifts were small and not statistically significant. However, some individuals experienced deteriorations, especially in visual acuity at near distances (n = 7 for the right eye, n = 6 for the left). Participants over 40 years of age had 16.1 times higher odds of deterioration compared to those under 40 years (95% CI: 2.7–95.9, p = 0.002). The most commonly reported eye strains were eye fatigue (n = 32), rubbing (n = 25), and burning (n = 24). If smart glasses are to be implemented in logistics companies, it is recommended to offer employees eye tests with an industrial physician in advance.

Mobile Messsysteme zur Analyse von körperlichen Arbeitsbelastungen werden immer praktikabler. Dem präventiven Arbeitsschutz stehen unterschiedlich komplexe Systeme zur Verfügung, die sich für verschiedene Anwendungsfälle und -gruppen eignen. Die CUELA-Methode bietet Messmodule unterschiedlicher Komplexität, die die Belastungsfaktoren pro Körperregion analysieren und bewerten. Am Beispiel des CUELA-Schultermoduls wird das prinzipielle Vorgehen erläutert.