Riley E. Splittstoesser

Quantitative Dynamic Measures of Physical Exposure Predict Low Back Functional Impairment

Study Design. Prospective field study of work exposure and changes in back function. Objective. Quantify dynamic physical exposures in the workplace and their association with decreases in kinematic back function (indicative of low back pain [LBP]). Summary of Background Data. Previous epidemiologic studies of work have measured gross categories of exposure and found moderate relationships with LBP. More precise quantitative measures of exposure and spine function were hypothesized to increase the chances of identifying any significant associations. Methods. Three hundred and ninety real-time physical exposure measures were collected from distribution center workers performing repetitive manual materials handling tasks. Low back health effect measures were quantitatively measured prospectively for workers performing each of the jobs using a kinematic measure of function. Results. Significant decreases in spine function were observed in workers associated with 40% of the jobs sampled. Numerous significant univariate odds ratios were identified that indicated an association between physical exposure and decreased function. A multivariate model including right lateral trunk velocity, timing of the maximum dynamic asymmetric load moment exposure, and the magnitude of the dynamic sagittal bending moment predicted reduced spine function well. The model resulted in excellent sensitivity (85%) and specificity (87.5%) as well as excellent positive predictive value (89.5%) and negative predictive value (82.4%). Conclusion. This study suggests that with proper quantification of job exposure and spine function, it is possible to identify which dynamic physical exposures are associated with reduced spine function and increases in LBP.

Grip force and muscle activity differences due to glove type.

The purpose of this study was to investigate the effects of different types and sizes of gloves on external grip force and muscle activity. Twenty-one male and seven female volunteers served as subjects. Each subject performed two maximum voluntary grip contractions while wearing each of the 10 glove types. Results indicated significant differences in the effects of different glove types on the peak force, ratio of peak force to normalized flexor muscle EMG activity, and the ratio of peak force to coactivity.

Quantitative biomechanical workplace exposure measures: Distribution centers

Physical work exposure characteristics assessed in most previous epidemiologic studies have been described mostly in gross categorical terms (e.g. heavy work, lifting and forceful movements, etc.) and have resulted in relatively moderate associations with low back pain risk. We hypothesized that it was necessary to characterize work demands in a much more quantitative fashion so that the precise biomechanically meaningful measures of exposure were available for risk analysis. In this study, we used sophisticated instrumentation to continuously document 390 physical exposures during lifting (in four types of distribution centers) throughout work. This study profiles these exposures and shows how these exposures vary as a function of the type of distribution center and compares the exposures to (previously documented) manufacturing exposures. Static load and load moment measures were found to greatly under-represent true (dynamic) load and load moment exposures to workers. Lift durations averaged 11-12% of the cycle time in distribution environments. This study indicates that distribution workers are commonly exposed to greater extreme loads and move much more rapidly than manufacturing employees. The information provided here can serve as a basis for low back pain risk assessments.

Instrumentation for measuring dynamic spinal load moment exposures in the workplace

Prior research has shown the load moment exposure to be one of the strongest predictors of low back disorder risk in manufacturing jobs. However, to extend these finding to the manual lifting and handling of materials in distribution centers, where the layout of the lifting task changes from one lift to the next and the lifts are highly dynamic, would be very challenging without an automated means of quantifying reach distances and item weights. The purpose of this paper is to describe the development and validation of automated instrumentation, the Moment Exposure Tracking System (METS), designed to capture the dynamic load moment exposures and spine postures used in distribution center jobs. This multiphase process started by obtaining baseline data describing the accuracy of existing manual methods for obtaining moment arms during the observation of dynamic lifting for the purposes of benchmarking the automated system. The process continued with the development and calibration of an ultrasonic system to track hand location and the development of load sensing handles that could be used to assess item weights. The final version of the system yielded an average absolute error in the loads moment arm of 4.1cm under the conditions of trunk flexion and load asymmetry. This compares well with the average absolute error of 10.9cm obtained using manual methods of measuring moment arms. With the item mass estimates being within half a kilogram, the instrumentation provides a reliable and valid means for assessing dynamic load moment exposures in dynamic distribution center lifting tasks.

Developing Physical Exposure-Based Back Injury Risk Models Applicable to Manual Handling Jobs in Distribution Centers

Using our ultrasound-based “Moment Monitor,” exposures to biomechanical low back disorder risk factors were quantified in 195 volunteers who worked in 50 different distribution center jobs. Low back injury rates, determined from a retrospective examination of each companys Occupational Safety and Health Administration (OSHA) 300 records over the 3-year period immediately prior to data collection, were used to classify each jobs back injury risk level. The analyses focused on the factors differentiating the high-risk jobs (those having had 12 or more back injuries/200,000 hr of exposure) from the low-risk jobs (those defined as having no back injuries in the preceding 3 years). Univariate analyses indicated that measures of load moment exposure and force application could distinguish between high (n = 15) and low (n = 15) back injury risk distribution center jobs. A three-factor multiple logistic regression model capable of predicting high-risk jobs with very good sensitivity (87%) and specificity (73%) indicated that risk could be assessed using the mean across the sampled lifts of the peak forward and or lateral bending dynamic load moments that occurred during each lift, the mean of the peak push/pull forces across the sampled lifts, and the mean duration of the non-load exposure periods. A surrogate model, one that does not require the Moment Monitor equipment to assess a jobs back injury risk, was identified although with some compromise in model sensitivity relative to the original model.

Cumulative Spine Loading and Clinically Meaningful Declines in Low-Back Function

Objective: The objective was to assess the role of cumulative spine loading measures in the development of a clinically meaningful decline in low-back function. Background: Cumulative spine loading has been a suspected risk factor for low-back pain for many years, yet the measures that characterize risk have not been well delineated. Methods: A total of 56 cumulative exposure measures were collected in a prospective field study of distribution center workers. An individual’s risk for a clinically meaningful decline in low-back function (true cases) was explored with daily, weekly, and job tenure cumulative exposure measures using univariate and multivariate statistical modeling techniques. True noncases were individuals with no decline in low-back function. Results: An individual’s risk for a clinically meaningful decline in low-back function (true cases) was predicted well versus true noncases (sensitivity/specificity = 72%/73%) using initial low-back function (p(n)), cumulative rest time, cumulative load exposure, job satisfaction, and worker age. Conclusions: Cumulative rest time was identified as an important component for predicting an individual’s risk for a clinically meaningful decline in low-back function. Application: This information can be used to assess cumulative spine loading risk and may help establish guidelines to minimize the risk of a clinically meaningful decline in low-back function.

Musculoskeletal disorder risk during automotive assembly: current vs. seated.

Musculoskeletal disorder risk was assessed during automotive assembly processes. The risk associated with current assembly processes was compared to using a cantilever chair intervention. Spine loads and normalized shoulder muscle activity were evaluated during assembly in eight regions of the vehicle. Eight interior cabin regions of the vehicle were classified by reach distance, height from vehicle floor and front to back. The cantilever chair intervention tool was most effective in the far reach regions regardless of the height. In the front far reach regions both spine loads and normalized shoulder muscle activity levels were reduced. In the middle and close reach regions spine loads were reduced, however, shoulder muscle activity was not, thus an additional intervention would be necessary to reduce shoulder risk. In the back far reach region, spine loads were not significantly different between the current and cantilever chair conditions. Thus, the effectiveness of the cantilever chair was dependent on the region of the vehicle.

Musculoskeletal disorder risk as a function of vehicle rotation angle during assembly tasks

Musculoskeletal disorders (MSD) are costly and common problem in automotive manufacturing. The research goal was to quantify MSD exposure as a function of vehicle rotation angle and region during assembly tasks. The study was conducted at the Center for Occupational Health in Automotive Manufacturing (COHAM) Laboratory. Twelve subjects participated in the study. The vehicle was divided into seven regions, (3 interior, 2 underbody and 2 engine regions) representative of work areas during assembly. Three vehicle rotation angles were examined for each region. The standard horizontal assembly condition (0° rotation) was the reference frame. Exposure was assessed on the spine loads and posture, shoulder posture and muscle activity, neck posture and muscle activity as well as wrist posture. In all regions, rotating the vehicle reduced musculoskeletal exposure. In five of the seven regions 45° of vehicle rotation represented the position that reduced MSD exposure most. Two of the seven regions indicated 90° of vehicle rotation had the greatest impact for reducing MSD exposure. This study demonstrated that vehicle rotation shows promise for reducing exposure to risk factors for MDS during automobile assembly tasks.

Are Workers Who Leave a Job Exposed to Similar Physical Demands as Workers Who Develop Clinically Meaningful Declines in Low-Back Function?

Objective: The objective is to quantify differences in physical exposures for those who stayed on a job (survivor) versus those who left the job (turnover). Background: It has been suggested that high physical job demands lead to greater turnover and that turnover rates may supplement low-back disorder incidence rates in passive surveillance systems. Method: A prospective study with 811 participants was conducted. The physical exposure of distribution center work was quantified using a moment monitor. A total of 68 quantitative physical exposure measures in three categories (load, position, and timing) were examined. Low-back health function was quantified using the lumbar motion monitor at baseline and 6-month follow-up. Results: There were 365 turnover employees within the 6-month follow-up period and 446 “survivors” who remained on the same job, of which 126 survivors had a clinically meaningful decline in low-back functional performance (cases) and 320 survivors did not have a meaningful decline in low-back functional performance (noncases). Of the job exposure measures, 6% were significantly different between turnover and cases compared to 69% between turnover and noncases. Turnover employees had significantly greater exposure compared to noncases. Conclusion: Turnover employees had similar physical job exposures to workers who remained on the job and had a clinically meaningful decline in low-back functional performance. Thus, ergonomists and HR should be aware that high turnover jobs appear to have similar physical exposure as those jobs that put workers at risk for a decline in low-back functional performance.

The Effectiveness of Whole Body and Localized Measures of Fatigue

Localized muscle fatigue in the back, with a resulting decrease in muscle force production, may increase risk of injury. Numerous methods have been used to assess fatigue in the back during materials handling, but many of these methods remain questionable as to what they are actually measuring. The goal of this study was to compare five different methods for measuring fatigue resulting from dynamic lifting, and to determine which methods correlate best with fatigue. Eight subjects performed sagittally symmetric lifts at a frequency of 12 lifts per minute for 60-minutes. Throughout the experiment, VO2, heart rate, local muscle oxygenation measured by Near Infrared Spectroscopy (NIRS), and subjective feedback was recorded. The whole body measures, VO2 and heart rate, were weakly correlated with the localized measures of NIRS and spectral analysis. Few of these correlations were significant, and none showed strong relationships. The subjective measures correlated well with NIRS. The results of this study suggest current measures of fatigue may not assess the risk of fatigue to a particular muscle. It is important that more comparative studies are done to better the understanding of fatigue and what is being measured by common measures of fatigue. Additional studies should be done, particularly for the more quantitative, localized, measures such as NIRS.