Donald S. Bloswick

Biomechanical simulation of manual lifting using spacetime optimization

Previous optimization techniques for the prediction of lifting motion patterns often require a change in either the number of variables or the order of the mathematical functions used to express the angular displacement of selected joints in response to change in variant conditions. The resolution of predicted results can also be seriously constrained by the number of variables used. These restrictions may often limit the applicability of these methodologies. In this paper, we proposed a new methodology for generating the optimum motion patterns for para-sagittal lifting tasks. A detailed description of this methodology is introduced. An example of an analysis using this methodology is presented. The computer program generated lifting motion patterns with a reduction of the overall objective function values. The actual versus predicted lifting motion patterns are compared. Using this method, constraints can be added anywhere within the lifting cycle without the need of rewriting the whole program. These features provide for a more flexible and efficient prediction of the lifting motion.

The NIOSH Lifting Equation and Low-Back Pain, Part 1 Association With Low-Back Pain in the Backworks Prospective Cohort Study

Objective: The aim of this study was to evaluate relationships between the revised NIOSH lifting equation (RNLE) and risk of low-back pain (LBP). Background: The RNLE is commonly used to quantify job physical stressors to the low back from lifting and/or lowering of loads. There is no prospective study on the relationship between RNLE and LBP that includes accounting for relevant covariates. Method: A cohort of 258 incident-eligible workers from 30 diverse facilities was followed for up to 4.5 years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, hobbies, and current LBP were obtained at baseline. The cohort was followed monthly to ascertain development of LBP and quarterly to determine changes in job physical exposure. The relationship between LBP and peak lifting index (PLI) and peak composite lifting index (PCLI) were tested in multivariate models using proportional hazards regression. Results: Point and lifetime prevalences of LBP at baseline were 7.1% and 75.1%, respectively. During follow-up, there were 123 incident LBP cases. Factors predicting development of LBP included job physical exposure (PLI and PCLI), history of LBP, psychosocial factors, and housework. In adjusted models, risk (hazard ratio [HR]) increased per-unit increase in PLI and PCLI (p = .05 and .02; maximum HR = 4.3 and 4.2, respectively). PLI suggested a continuous increase in risk with an increase in PLI, whereas the PCLI showed elevated, but somewhat reduced, risk at higher exposures. Conclusion: Job physical stressors are associated with increased risk of LBP. Data suggest that the PLI and PCLI are useful metrics for estimating exposure to job physical stressors.

An ergonomic analysis of the ladder climbing activity

Abstract Injuries from slips, falls and overexertion during ladder climbing activities are common in both occupational and non-occupational environments. Little is known, however, about the task, equipment, and user parameters which may cause these injuries. In order to evaluate the hazards associated with ladder climbing, ten male subjects were tested under combinations of ladder rung separation, ladder slant, climbing speed, and climbing direction. Hand and foot forces, hand torques, torso muscle EMGs and hand and foot locations on the ladder rungs were recorded. A biomechanical model was developed which allowed the evaluation of dynamic joint moments and back forces. Study results include safety and biomechanical design guidelines relating to the effect of the task, equipment, and user parameters on climbing safety. Under the conditions studied there does not appear to be a significant slip hazard for people with reasonable strength and mobility. There may be a potential for climber grip strength to be exceeded under some field conditions and foot slip is possible during the use of vertical ladders. There is also the potential for localized fatigue in muscles acting at the elbow, hip and ankle joints during long climbs. The relatively high measured torso muscle IEMG suggests that certain ladder climbing activities may generate considerable back forces.

The WISTAH hand study: A prospective cohort study of distal upper extremity musculoskeletal disorders

BackgroundFew prospective cohort studies of distal upper extremity musculoskeletal disorders have been performed. Past studies have provided somewhat conflicting evidence for occupational risk factors and have largely reported data without adjustments for many personal and psychosocial factors.Methods/designA multi-center prospective cohort study was incepted to quantify risk factors for distal upper extremity musculoskeletal disorders and potentially develop improved methods for analyzing jobs. Disorders to analyze included carpal tunnel syndrome, lateral epicondylalgia, medial epicondylalgia, trigger digit, deQuervain’s stenosing tenosynovitis and other tendinoses. Workers have thus far been enrolled from 17 different employment settings in 3 diverse US states and performed widely varying work. At baseline, workers undergo laptop administered questionnaires, structured interviews, two standardized physical examinations and nerve conduction studies to ascertain demographic, medical history, psychosocial factors and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of musculoskeletal disorders. Repeat nerve conduction studies are performed for those with symptoms of tingling and numbness in the prior six months. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. Case definitions have been established. Point prevalence of carpal tunnel syndrome is a combination of paraesthesias in at least two median nerve-served digits plus an abnormal nerve conduction study at baseline. The lifetime cumulative incidence of carpal tunnel syndrome will also include those with a past history of carpal tunnel syndrome. Incident cases will exclude those with either a past history or prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.DiscussionA prospective cohort study of distal upper extremity musculoskeletal disorders is underway and has successfully enrolled over 1,000 workers to date.

Impact of the OSHA trench and excavation standard on fatal injury in the construction industry.

Learning ObjectivesRecall the past effectiveness—or lack thereof—of OSHA in lowering injury rates in the workplace, and the influence of the MSHA (Mine Safety and Health Administration) in the coal mining industry.Describe the course of fatal injury rates before and after revision of an ambiguous consensus standard governing trench and excavation jobs, along with introduction of a targeted inspection program in 1990.Explain whether and how changes in fatality rates depend on the size of construction firms and whether or not workers are unionized. In 1989 the US Occupational Safety & Health Administration revised the excavation and trenching standard. We examined fatal injuries from trench cave-in in the construction industry for five year periods before and after the revision in the 47 US states for which data were available for both periods. There was a 2-fold decline in the rate of fatal injury after revision of the standard, which substantially exceeded the decline in other causes of fatal injury in the construction industry during the same period. The decline was somewhat greater in large business firms but was evident in construction firms of all size classes. The fatality rate from trench cave-in in union construction workers was approximately half that of nonunion workers, but we were unable to determine whether this was best explained by union status, employment of union workers at larger construction firms, or both. This study provides evidence for the effectiveness of OSHA regulation in preventing fatal work injury.

A revised back compressive force estimation model for ergonomic evaluation of lifting tasks

Occupational back pain and injury are common and costly issues. Biomechanical models are often used to quantify job risk by estimating back muscle forces. In general, the most accurate models are also the most complex, creating demand for models that are both straightforward and accurate. An existing, basic hand-calculation back compressive force estimation model (HCBCF v1.0) was revised in two iterations to reduce the error induced by original simplifying assumptions. Lifting tasks (n=6000) from observational data were used to compare the HCBCF models with the University of Michigan 3D Static Strength Prediction Program (3DSSPP) The greatest r(2) (0.97) between the HCBCF v1.2 and the 3DSSPP was achieved with gender-specific equations designed to account for differences between males and females and a more detailed estimation of torso flexion angle and upper body mass center location. This gender-specific back compression and risk estimation model is a relatively simple alternative to computer-based back compressive force models. In addition the hand-calculation can be used as a general survey tool to determine which jobs should be analyzed with more sophisticated computer-based models.

Study protocol title: a prospective cohort study of low back pain

BackgroundFew prospective cohort studies of workplace low back pain (LBP) with quantified job physical exposure have been performed. There are few prospective epidemiological studies for LBP occupational risk factors and reported data generally have few adjustments for many personal and psychosocial factors.Methods/designA multi-center prospective cohort study has been incepted to quantify risk factors for LBP and potentially develop improved methods for designing and analyzing jobs. Due to the subjectivity of LBP, six measures of LBP are captured: 1) any LBP, 2) LBP ≥ 5/10 pain rating, 3) LBP with medication use, 4) LBP with healthcare provider visits, 5) LBP necessitating modified work duties and 6) LBP with lost work time. Workers have thus far been enrolled from 30 different employment settings in 4 diverse US states and performed widely varying work. At baseline, workers undergo laptop-administered questionnaires, structured interviews, and two standardized physical examinations to ascertain demographics, medical history, psychosocial factors, hobbies and physical activities, and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of low back pain. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. The lifetime cumulative incidence of low back pain will also include those with a past history of low back pain. Incident cases will exclude prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.DiscussionData analysis of a prospective cohort study of low back pain is underway and has successfully enrolled over 800 workers to date.

Job Level Risk Assessment Using Task Level Strain Index Scores: A Pilot Study

This paper explores 2 methods of modifying the Strain Index (SI) to assess the ergonomic risk of multi-task jobs. Twenty-eight automotive jobs (15 cases and 13 controls) were studied. The first method is based on the maximum task SI score, and the second method is modeled on the NIOSH Composite Lifting Index (CLI) algorithm, named cumulative assessment of risk to the distal upper extremity (CARD). Significant odds ratios of 11 (CI 1.7–69) and 24 (CI 2.4–240) were obtained using the modified maximum task and CARD, respectively. This indicates that modification of the SI may be useful in determining the risk of distal upper extremity injury associated with a multi-task job.

Ergonomic risk exposure and upper-extremity cumulative trauma disorders in a maquiladora medical devices manufacturing plant.

Workers at a Nogales, Mexico, maquiladora plant that assembles medical devices were studied to determine the prevalence of upper-extremity cumulative trauma disorders (CTD). Subjects included production workers employed 6 months or longer; of the 148 eligible workers, 145 (98%) participated. Subjects had a mean age of 24.6 years (SD = 5.2; range, 17 to 45) and the mean length of employment was 3.5 years (SD = 2.5; range, 0.5 to 14). Job tasks were videotaped and analyzed for ergonomic risk factors, using pre-defined criteria. All jobs performed by study subjects were found to involve one or more ergonomic risk factors associated with the development of CTD. A CTD questionnaire and screening physical examination format, similar to that used by the National Institute of Occupational Safety and Health (NIOSH) in a chicken processing plant study, were administered. Period prevalence of CTD within the previous year, as reported on the questionnaire, was 28%. Prevalence of CTD was 17%, using data from the screening physical examination. Point prevalence (current pain data from the questionnaire plus positive symptoms on the screening physical examination) was 15%. CTD was reported more frequently in women than men (46% and 25%, respectively; P < 0.05) and in subjects who had worked at the plant less than one year (50%; P < 0.05). Workforce turnover (3% monthly) may have resulted in those affected by CTD leaving employment, reducing the apparent CTD rate in experienced workers.

Job Level Risk Assessment Using Task Level ACGIH Hand Activity Level TLV Scores: A Pilot Study

Existing upper extremity musculoskeletal disorder analytical tools are primarily intended for single or mono-task jobs. However, many jobs contain more than 1 task and some include job rotation. This case/control study investigates methods of modifying an existing tool, the American Conference of Governmental Industrial Hygienists (ACGIH) Hand Activity Level (HAL) Threshold Limit Value (TLV), to assess the upper extremity risk of multi-task jobs. Various methods of combining the task differences and ratios into a job level assessment were explored. Two methods returned significant odds ratios, (p < .05) of 18.0 (95% CI 1.8–172) and 12.0 (95% CI 1.2–120). These results indicate that a modified ACGIH HAL TLV may provide insight into the work-related risk of multi-task jobs. Further research is needed to optimize this process.