Ergonomics - Sprains, Strains, and Strategies

Ergonomics - Sprains, Strains, and Strategies

Tuesday, June 2, 2015, 10:30 AM - 12:30 PM

SR-113-01 Sitting time, Obesity, and Injury at Work

T. Lin, T. Courtney, D. Lombardi, S. Verma, Liberty Mutual Research Institute for Safety, Hopkinton, MA

Objective: Injuries pose a significant burden on working populations worldwide, and lately obesity has been suggested as a risk factor. We examined whether obesity was associated with injury at work, and then moved upstream along the causal chain to investigate whether time spent sitting at work contributed to weight gain.

Methods: Two studies were conducted using a nationally representative cohort, the National Longitudinal Survey of Youth 1979 (NLSY79). The first study evaluated the association between obesity and injury at work using generalized estimating equations (GEE) and random-effects logistic regression. Obesity was measured as body mass index (BMI) based on self-report height and weight, and demographic profiles (age, gender, education, race and ethnicity) and job characteristics (work hours, hourly wage, environmental hazards, physical demands, and industry) were incorporated as control variables. In the second study, we treated BMI as the outcome, and the primary explanatory variable was “time spent sitting” extracted from O*NET (Occupational Information Network) and linked to individuals in NLSY79. To assess the association between sitting time and BMI, we used fixed-effects models, which control for the effects of time-invariant factors. We included in the regression models additional time-varying variables such as leisure-time physical activities and work hours, and conducted a series of robustness checks.

Results: Results from the analyses were consistent with our hypotheses. For the first study, the GEE and random-effects regression indicated that obesity was associated with 25% or higher odds of injury at work [OR =1.25, 95%CI = 1.12-1.39, p < 0.001]. For the second study, longer sitting time at work was significantly associated with higher BMI for the overall sample (p < 0.05) and men (p < 0.01). For women, the association was not significant.

Conclusions: Our first study indicated that obesity may predispose employed U.S. adults to workplace injury, while the second provided further support for initiatives to reduce workplace sedentariness as a means of reducing the risk of obesity and related health and safety outcomes. Key study strengths included the use of nationally representative cohort data to examine these relationships prospectively across a broad range of industries and occupations as well as extensive robustness checks. Further research is needed to better clarify the mechanisms underlying both associations.

SR-113-02 Development of a Fatigue Failure-Based Ergonomics Assessment Tool for Low Back Disorder Risk

S. Gallagher, Auburn University, Auburn, AL

Objective: The objectives of this research were to examine the efficacy of using fatigue failure theory to develop a risk assessment tool for low back disorders and to evaluate this approach using a published database of low back disorders.

Methods: Data from cadaver studies of lumbar motion segments subject to fatigue loading at different percentages of ultimate strength (US) were analyzed using Weibull analysis. The resulting data was categorized into 5 categories based on estimated US of the specimens. The categories included < 30% US (19 specimens), 30-40% US (19 specimens), 40-50% US (21 specimens), 50-60% US (16 specimens), and > 60% US (15 specimens). Weibull analyses were performed on each category to estimate the distribution of cycles to failure for each category of ultimate strength. Non-linear regression was used on the characteristic life (n) to develop a relationship between cycles to failure and ultimate strength category. Results of this regression were then used to estimate the amount of damage expected per cycle at the different deciles of ultimate strength. To examine the relationship of the expected rate of damage accumulation at different level of US, an existing database published by Zurada et al. (1997) was used. For this analysis, it was assumed that the peak load moment was positively correlated with spinal loading. Both peak load moment and frequency of lifting data were divided into deciles of risk for the analysis. A “daily dose” of exposure was developed by multiplying the estimated damage per cycle (for a given peak moment decile) multiplied by the frequency of lifts (per hour) times 8 hours/day.

Results: A dose-response relationship was observed between the cumulative load estimates of the new assessment tool and the probability of high-risk group membership for low back disorders. The low risk condition (referent) was assigned a risk of 1.0. The odds ratios and confidence intervals for low back disorders for other risk levels were as follows: Low-Medium (OR=3.8, 95%CI = 1.1, 13.8), Medium (OR=6.7, 95%CI=1.9, 23.7), Medium-High (OR=7.8, 95%CI = 2.2, 26.9), and High (OR=11.9, 3.4, 42.1).

Conclusions: While numerous ergonomics exposure assessment tools have been developed to assess MSD risk, none to date have been predicated on fatigue failure theory. This study suggests the need for the development of MSD exposure assessment tools to evaluate injury risk using fatigue failure as a basis.

SR-113-03 Observation-Based Posture Assessment: Toward a Best Practice Approach

D. Andrews, P. Weir, University of Windsor, Windsor, ON, Canada; B. Lowe, NIOSH, Cincinnati, OH

Objective: This podium session will describe an observational approach for assessing postural stress of the trunk and upper limbs that is intended to improve risk analysis for prevention of musculoskeletal disorders in the workplace.

Methods: As outlined in a recent document published jointly by the National Institute for Occupational Safety and Health (NIOSH) in the United States and the Centre of Research Expertise for the Prevention of Musculoskeletal Disorders (CRE-MSD) in Canada, this approach is founded in recent research evidence and was developed to help practitioners. These studies have evaluated how much time it takes observers to classify specific trunk and upper limb postures, how frequently observers are likely to make posture classification errors, and the magnitude of these errors. The frequency and magnitude of posture classification errors depend on how many categories (lev­els) are available from which to classify the specific posture.

Results: Experimental evidence suggests that optimal posture analysis performance is obtained by partitioning trunk flex­ion range of motion into 4 categories of 30° increments; trunk lateral bend into 3 categories of 15° increments; shoulder flexion into 5 categories of 30°; shoulder abduction into 5 categories of 30°; and elbow flexion into 4 categories of 30°. These categories are suggested because they optimize how rapidly and accurately ana­lysts can visually judge posture. This presentation will offer several general guidelines for the video recording of posture (e.g., camera position, field of view, lighting, duration of recording) and for the posture analysis process (e.g., benefits of digital video, computer software, training, use of visual references).

Conclusions: The new document, US DHHS (NIOSH) publication 2014-131, is freely available online (, and can assist health/safe­ty, ergonomics, and risk management/loss control practitioners who conduct job/worksite assessments of lifting, pushing, pulling, carrying, and/or manual handling risk factors.

CS-113-04 Evaluating and Improving Short and Long Term Shoulder Injury Risk

C. Shulenberger, Bureau Veritas North America, Inc., Ashland, OR

Situation/Problem: Evaluating and improving the short and long term risk of shoulder injuries are quite complex. Currently there is no consensus Shoulder Risk Assessment Model exists like that for Manual Material Handling and the Distal Upper Extremities.

Resolution: A recent review of the literature indicated that the following factors have shown significance to shoulder injuries (odds ratio) but only in combination with other risk factors. Forceful exertion- Applied force has the highest relationship to injury development. Shoulder posture- Overhead work is shown to be a critical factor in most studies. Direction of movement- The direction of movement also impacts relative strength and shoulder stability. Repetition- This factor is confounding because with very light loads the odds ratio actually goes down in some studies. Muscle fatigue- Impacts a worker’s MVC and therefore applied force. Therefore, injury risk is impacted by recovery time. Body work posture- Shoulder strength varies in a standing, sitting or kneeling work posture. Gender and Aging- Females typically demonstrate 55-65% of male upper extremity strength. Aging is often associated with previous exposures (cumulative trauma and/or previous injury) and decreased strength

Results: 1. Applied Force was the most critical risk factor. 2. Posture and Repetition without consideration for Force were not as significant. 3. Aging and Gender related factors should not be ignored when evaluating shoulder risk. 4. Currently a usable model for assessing shoulder risk like the EHS professional has for Manual Material Handling and Distal Upper Extremities does not exist. Therefore, further efforts in this area are necessary.

Lessons Learned: 1. Determine what your company means by High, Medium, Low Risk and OK and provide percentile definitions. 2. Utilize Existing Workers Compensation data (short term) to target existing Tasks/Jobs for Risk Assessment and Improvement (short term). 3. Develop Design and Operational Guidelines to reflect the Risk Guidelines and apply the As Low As Reasonably Possible (ALARP) approach per ANSI 590.3 (medium term). 4. Work with researchers to develop a Risk Model that integrates Force, Posture and Repetition based as best possible (consistent with) on the ongoing research findings (long term).

CS-113-05 A Proposed Mobile Application to Include Multiple Ergonomic Assessment Tools

N. Ketzler, S. Gallagher, R. Sesek, C. Seals, R. Thomas, Auburn University, Auburn, AL; S. Gibson, Ergonomics Applications, Salem, SC

Situation/Problem: Multiple ergonomic assessment tools are freely available to practitioners in the workplace. Many of these tools are used on the go, often paper forms on a clipboard. Paper-based versions of ergonomic assessment tools may not be the most efficient analysis method, particularly since one does not get immediate feedback. Our goal was to develop a mobile application to assess ergonomic risks for different tasks. The application incorporates multiple ergonomic assessment tools commonly used by ergonomists into one platform. The application also utilizes the new flowcharts that have been incorporated into the AIHA Ergonomic Toolkit.

Resolution: A case study was then performed by a group of ergonomists with varying levels of ergonomics expertise to determine the usability of the mobile application. Different workplace tasks were analyzed using the mobile application to assess the risk of each task. The mobile application was compared to the original paper-based method to determine the increase in efficiency.

Results: Users found the mobile application to be more efficient and easier to use than the original paper-based copies of the ergonomic assessment tools in the workplace.

Lessons Learned: Mobile Applications have the potential to enhance the availability and application of existing ergonomic assessment procedures and tools.

CS-113-06 The Aging Workforce: Changes in Muscle Physiology

B. McGowan, Humantech, Inc., Ann Arbor, MI

Situation/Problem: In 2009, older workers (55 and over) represented 19% of the U.S. workforce. This group is the nation’s fastest growing segment of the workforce. The Bureau of Labor Statistic projects, for the period between 2006 and 2016, that there will be an 84.3% increase in workers age 75 and over, an 83.4% increase in workers between the ages of 65 and 74, and a 36.5% increase in workers between ages of 55 and 64. Many industrial job duties require physical demands such as lifting, lowering, pushing, pulling, bending, twisting, reaching, climbing, and kneeling, among others. Each of these job demands require forceful, repetitive, or sustained muscle contractions. For the younger worker, the physical capabilities for job duties are well defined and have resulted in the publication of several design standards. Unfortunately, the physical capabilities of the older worker have not been studied as extensively, and as a result, design standards for older workers are hard to find. The purpose of this presentation is to summarize the muscle physiology changes that occur as we age and to propose design standards for the aging workforce.

Resolution: Research was conducted to find citations related to changes in muscle physiology as we age. Topics of interest included changes to sensory/motor perception and control, strength, movement control, and cardiovascular capacity.

Results: The review of literature found several key changes in muscle physiology as we age. There is a loss of muscle mass and strength, and a consequent functional impairment that occurs starting at 40 years old and continues with increasing age. Key performance changes that occur as a result of the changes in muscle physiology as we age include: 1) movement speed slows during grasping and reaching, 2) movement precision (deceleration) decreases, 3) range of motion is reduced, 4) muscle strength decreases, 5) force control decreases, as adults grip twice as hard to compensate, 6) force perception decreases, and 7) muscle endurance decreases. Based on these findings, design standards for lifting, lowering, pushing, pulling, bending, twisting, reaching, climbing, and kneeling were developed for the aging workforce.

Lessons Learned: The changes in muscle physiology as we age are real, and impact workers capabilities to perform work. Understanding the capabilities of the older worker allowed for the development of design standards to optimize performance and to minimize musculoskeletal disorders for the aging workforce.​