Mark C. Schall

Accuracy and repeatability of an inertial measurement unit system for field-based occupational studies

Abstract The accuracy and repeatability of an inertial measurement unit (IMU) system for directly measuring trunk angular displacement and upper arm elevation were evaluated over eight hours (i) in comparison to a gold standard, optical motion capture (OMC) system in a laboratory setting, and (ii) during a field-based assessment of dairy parlour work. Sample-to-sample root mean square differences between the IMU and OMC system ranged from 4.1° to 6.6° for the trunk and 7.2°–12.1° for the upper arm depending on the processing method. Estimates of mean angular displacement and angular displacement variation (difference between the 90th and 10th percentiles of angular displacement) were observed to change <4.5° on average in the laboratory and <1.5° on average in the field per eight hours of data collection. Results suggest the IMU system may serve as an acceptable instrument for directly measuring trunk and upper arm postures in field-based occupational exposure assessment studies with long sampling durations. Practitioner Summary: Few studies have evaluated inertial measurement unit (IMU) systems in the field or over long sampling durations. Results of this study indicate that the IMU system evaluated has reasonably good accuracy and repeatability for use in a field setting over a long sampling duration.

Musculoskeletal disorders as a fatigue failure process: evidence, implications and research needs

Abstract Mounting evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in musculoskeletal tissues. Evaluations of MSD risk in epidemiological studies and current MSD risk assessment tools, however, have not yet incorporated important principles of fatigue failure analysis in their appraisals of MSD risk. This article examines the evidence suggesting that fatigue failure may play an important role in the aetiology of MSDs, assesses important implications with respect to MSD risk assessment and discusses research needs that may be required to advance the scientific community’s ability to more effectively prevent the development of MSDs. Practitioner Summary: Evidence suggests that musculoskeletal disorders (MSDs) may result from a fatigue failure process. This article proposes a unifying framework that aims to explain why exposure to physical risk factors contributes to the development of work-related MSDs. Implications of that framework are discussed.

Evaluation of four sensor locations for physical activity assessment.

Direct measurements of physical activity (PA) obtained with inertial measurement units (IMUs) secured to the upper arms and trunk of 36 registered nurses working a full shift were compared to measurements obtained with a commercially-available PA monitor (ActiGraph wGT3X-BT) worn at the waist. Raw accelerations from each device were summarized into PA counts/min and metabolic equivalent (METs) categories using standard definitions. Differences between measurements were examined using repeated measures one-way analyses of variance (ANOVA) and agreement was assessed using Bland-Altman plots. Statistically significant differences were observed between all sensor locations for all PA summary metrics except for between the left and right arm for percentages of work time in the light and moderate counts/min categories. Bland-Altman plots suggested limited agreement between measurements obtained with the IMUs and measurements obtained with the wGT3X-BT waist-worn PA monitor. Results indicate that PA measurements vary substantially based on sensor location.

Working postures and physical activity among registered nurses.

Nurses report a high prevalence of musculoskeletal discomfort, particularly of the low back and neck/shoulder. This study characterized the full-shift upper arm and trunk postures and movement velocities of registered nurses using inertial measurement units (IMUs). Intensity of occupational physical activity (PA) was also ascertained using a waist-worn PA monitor and using the raw acceleration data from each IMU. Results indicated that nurses spent a relatively small proportion of their work time with the arms or trunk in extreme postures, but had few opportunities for rest and recovery in comparison to several other occupational groups. Comparisons between nurses in different PA groups suggested that using a combination of accelerometers secured to several body locations may provide more representative estimates of physical demands than a single, waist-worn PA monitor. The findings indicate a need for continued field-based research with larger sample sizes to facilitate the development of maximally effective intervention strategies.

Characterizing exposure to physical risk factors among reforestation hand planters in the Southeastern United States

Low back and neck/shoulder pain are commonly reported among reforestation hand planters. While some studies have documented the intensive cardiovascular demands of hand planting, limited information is available regarding exposures to physical risk factors associated with the development of musculoskeletal disorders (MSDs) among hand planters. This study used surface electromyography (EMG) and inertial measurement units (IMUs) to characterize the muscle activation patterns, upper arm and trunk postures, movement velocities, and physical activity (PA) of fourteen Southeastern reforestation hand planters over one work shift. Results indicated that hand planters are exposed to physical risk factors such as extreme trunk postures (32.5% of time spent in ≥45° trunk flexion) and high effort muscle exertions (e.g., mean root-mean-square right upper trapezius amplitude of 54.1% reference voluntary exertion) that may place them at increased risk for developing MSDs. The findings indicate a need for continued field-based research among hand planters to identify and/or develop maximally effective interventions.

Wearable Technologies: How Will We Overcome Barriers to Enhance Worker Performance, Health, And Safety?

Wearable technologies are changing the way that people interact with the world. Personal physical activity monitors are becoming ubiquitous in our society and are helping to advance user health and performance, yet, many workplaces have not broadly adopted the technologies beyond either low fidelity/complexity pedometer-based applications or, inversely, high fidelity/complexity lab- based evaluations. Considering adoption of wearable technologies in the workplace, some technology-related concerns include; (1) types of data needed to be captured (motion, muscle, temperature, etc.), (2) constraints of sensor design, such as human-sensor system integration (embedded in clothing versus strapped to person), ruggedness, form factor, or weight, and (3) types of data interpretation and feedback applications that exist to translate data into useful information (communication, trend mapping, situational awareness). From the research design perspective, there is difficulty in conducting studies capable of demonstrating a safety or productivity that supports employing wearable technology in the workplace. Difficulties include poor access to workplaces and varied worker populations to conduct research, lack of funding, and the need for extended time periods to demonstrate utility (often longer than the lifecycle of the technology in question). Considering the industry perspective, barriers to adopting wearable technologies include lack of convincing data, cost, and anticipation of reduced productivity, poor usability, and/or information overload. Additionally, employee privacy concerns and public policy implications may provide challenges. Another potential barrier may be that some practitioners, however, believe that innovative technologies may be adopted without rigorous testing. This may have short term success to garner interest but may create a barrier to adoption in the long term if the devices are found to have no near or mid- term efficacy. The overarching goal of the session will be to improve understanding of different perspectives as it relates to the use, barriers, and adoption of wearable technologies and generate discussion for overcoming such barriers to improve the process of research to practice to research (RtPtR). The panelists are from a variety of industry sectors and academia. The session will begin with a 5- minute introductory statement from each panelist; therefore, most of the session will be a discussion between panelists and audience.

Improving the risk assessment capability of the revised NIOSH lifting equation by incorporating personal characteristics

The impact of manual material handling such as lifting, lowering, pushing, pulling and awkward postures have been studied, and models using these external demands to assess risk of injury have been developed and employed by safety and health professionals. However, ergonomic models incorporating personal characteristics into a comprehensive model are lacking. This study explores the utility of adding personal characteristics such as the estimated L5/S1 Intervertebral Disc (IVD) cross-sectional area, age, gender and Body Mass Index to the Revised NIOSH Lifting Equation (RNLE) with the goal to improve risk assessment. A dataset with known RNLE Cumulative Lifting Indices (CLIs) and related health outcomes was used to evaluate the impact of personal characteristics on RNLE performance. The dataset included 29 cases and 101 controls selected from a cohort of 1022 subjects performing 667 jobs. RNLE risk assessment was improved by incorporation of personal characteristics. Adding gender and intervertebral disc size multipliers to the RNLE raised the odds ratio for a CLI of 3.0 from 6.71 (CI: 2.2-20.9) to 24.75 (CI: 2.8-215.4). Similarly, performance was either unchanged or improved when some existing multipliers were removed. The most promising RNLE change involved incorporation of a multiplier based on the estimated IVD cross-sectional area (CSA). Results are promising, but confidence intervals are broad and additional, prospective research is warranted to validate findings.

An Optimization Framework for Job Rotation to Better Assess the Impact on Overall Risk

We aim to study the potential of job rotation schemes to improve worker safety. To this end, we developed a novel optimization framework based on a recently proposed fatigue-failure model for musculoskeletal disorder (MSD) risk evaluation. We then employed it to conduct an illustrative case study. We demonstrate that the effect of job rotation is highly dependent on the composition of the job pool. Namely, if the job pool contains high-risk tasks (e.g., those carrying greater than 90% probability of developing a disorder), then it may be impossible to observe any risk improvement with rotations alone. On the other hand, if all jobs are already relatively low-risk, then a rotation may be very helpful in achieving risk equity.

Heart Rate and Perceived Exertion Among Young Adult Obese Males During One-Handed Carrying

Obesity is an increasing problem across the globe that has been strongly associated with work-related injury. One-handed carrying is considered one of the most fatiguing methods of load carrying. The objective of this study was to examine the effects of obesity and load magnitude on heart rate and ratings of perceived exertion among young adult males during one-handed carrying. Load magnitude was observed to have a statistically significantly effect on heart rate and perceived exertion of the arm, back and whole body, whereas obesity was significant only for perceived exertion of the arm. The results suggest that young adult obese males can carry similar loads as young adult non-obese males without having a statistically significant increase in heart rate or perceived exertion. However, more research is needed to validate these results for longer distances and carrying times.

Digital Human Modeling in the Occupational Safety and Health Process: An Application in Manufacturing

OCCUPATIONAL APPLICATIONS Digital human modeling and simulation software has been identified as an effective tool for evaluating work tasks and design alternatives without requiring the expense of physical mock-ups and production trials. Despite recent commercial advancements and a broader availability of digital human modeling platforms, the peer-reviewed scientific literature lacks sufficient demonstration of the application of digital human modeling software within an occupational safety and health process for mitigating exposures to physical risk factors in a real-work environment. We describe the implementation of a commercially available digital human modeling platform as a component of an occupational safety and health process in a manufacturing environment over the course of 1 year. Success stories, challenges, and practical recommendations are discussed.