A comparison of peak vs cumulative physical work exposure risk factors for the reporting of low back pain in the automotive industry

Task rotation effects on upper extremity and back muscle activity

Job rotation is an intuitive approach to distributing work to minimize muscular fatigue. The purpose of the current study was to evaluate rotation between lifting and gripping on muscle activity and effort. Ten male participants performed all 4 combinations of two 15 min tasks in 30 min trials split between separate days to prevent fatigue. The tasks of lifting a 12 kg box and gripping at 20% of maximum were performed 6 times per minute (5 s work: 5 s rest). Muscle activity (percentiles, gaps) and perceived effort were significantly affected by the task combinations. The forearm and upper erector spinae muscles did not benefit as greatly from rotating between lifting and gripping tasks as the lower erector spinae, deltoid or trapezius. In addition to gross task differences, overlaps in muscle activity between "low back" and "upper extremity" tasks must be considered when creating effective job rotation schemes.

The interaction between skill, postures, forces and back pain in wool handling

Wool handling is an important rural occupation where workers process 200 or more fleeces daily, separating them into various quality components. Loads and postures they experience carry substantial risk of low back pain (LBP). Although a formal skill training structure exists, interaction with loads and LBP is unknown. We examined whether skill and LBP influenced trunk postures and loads of 60 wool handlers representing 3 skill levels. LBP prevalence ranged from 20% for junior (lowest skill) to 45% for open class (highest skill) wool handlers. Open class wool handlers demonstrated increased lateral bend and more axially twisted postures, generating greater medio-lateral shear forces and lateral bend and axial twist moments. LBP was associated with open class wool handlers spending more time in severe axially twisted postures. These findings suggest that skill-based training needs to be reviewed to reduce the quantity of axially twisted posture which may help reduce the prevalence of LBP in this workforce.

A comparison of low back kinetic estimates obtained through posture matching, rigid link modeling and an EMG-assisted model

This study examined errors introduced by a posture matching approach (3DMatch) relative to dynamic three-dimensional rigid link and EMG-assisted models. Eighty-eight lifting trials of various combinations of heights (floor, 0.67, 1.2 m), asymmetry (left, right and center) and mass (7.6 and 9.7 kg) were videotaped while spine postures, ground reaction forces, segment orientations and muscle activations were documented and used to estimate joint moments and forces (L5/S1). Posture matching over predicted peak and cumulative extension moment (p < 0.0001 for all variables). There was no difference between peak compression estimates obtained with posture matching or EMG-assisted approaches (p = 0.7987). Posture matching over predicted cumulative (p < 0.0001) compressive loading due to a bias in standing, however, individualized bias correction eliminated the differences. Therefore, posture matching provides a method to analyze industrial lifting exposures that will predict kinetic values similar to those of more sophisticated models, provided necessary corrections are applied.

Does vibration influence the initiation of intervertebral disc herniation? An examination of herniation occurrence using a porcine cervical disc model

STUDY DESIGN

In vitro biomechanics, randomized control trial.

OBJECTIVE

The objectives of this study were 2-fold: first, to determine the effect of exposure to axial vibration on the initiation and progression of disc herniation; second, to determine the effect of vibration exposure and the presence of disc damage on the mechanical properties of individual lamella from the annulus.

SUMMARY OF BACKGROUND DATA

Vibration exposure has been linked to a higher reporting of low back pain and disc herniation via epidemiological studies. However, these studies are unable to determine causal relationships. In vitro tissue experimentation assists in determining if certain exposures, for example vibration, actually lead to herniation.

METHODS

A total of 20 porcine (aged, 6-8 months; similar skeletal development as an adolescent human) functional spine units (FSU) were subjected to repetitive flexion-extension (6000 cycles), which has been shown to produce intervertebral disc herniation. While being exposed to the repeated flexion/extension, 10 FSUs were statically compressed under 1400 N (control group) and the other 10 were cyclically compressed (1260-1540 N) at a frequency of 5 Hz (vibration group). Post collection, intervertebral discs were dissected and individual lamella of the annulus was tested under uniaxial tension to failure (tension applied perpendicular to the orientation of the collagen fibers) to isolate the mechanical properties of the intralamellar matrix.

RESULTS

Of the 10 control FSUs, 4 had evidence of herniation initiation while 8 of the 10 vibrated FSUs showed herniation initiation (P ∇ 0.01). No significant differences in disc height loss or FSU stiffness were observed between the control and vibrated groups. Further, no signficant differences were observed between the 2 groups for any of the single lamella mechanical properties.

CONCLUSION

This study confirmed that vibration is a causal mechanical risk factor that significantly increases the occurrence of herniation.

Effect of initial horizontal object position on peak L5/S1 moments in manual lifting is dependent on task type and familiarity with alternative lifting strategies

This study investigated whether the effects of initial horizontal object position on peak L5/S1 total moment (PTM) are affected by task type or familiarity with alternative lifting strategies during manual lifting. Nine subjects lifted low-lying boxes from far and close initial horizontal positions in a typical laboratory lifting task (without any transportation of the load) and in a more realistic lifting task in which the box was transported to a location at a few metres distance. Subsequently, subjects were familiarised with alternative lifting strategies (e.g. shifting and tilting) and they then repeated the more realistic lifting task. Compared with the typical laboratory lifting task, the more realistic lifting task resulted in 6% larger PTMs for the close-positioned box. Familiarisation with alternative lifting techniques resulted in a 10% reduction in PTMs for the far-positioned box. As a result, the effect of initial horizontal box position on PTMs was smaller for the more realistic lifting task than for the typical laboratory lifting task and vanished after familiarisation with alternative lifting strategies. STATEMENT OF RELEVANCE: This study showed that the effect of horizontal box position on peak L5/S1 moments is dependent on the type of lifting task (comparing a typical laboratory simulated lifting task with a more realistic task involving carrying the load for a short distance) and familiarity with alternative lifting strategies. Therefore, it is recommended that back loading should be evaluated in a realistic simulation of the work situation or at the workplace itself.

The influence of kinesiophobia on trunk muscle voluntary responses with pre-programmed reactions during perturbation in patients with chronic low back pain

The purpose of this study was to examine the relation between fear of movement and perturbation induced electromyographic global trunk muscle voluntary responses with pre-programmed reactions among persons with chronic low back pain (CLBP). CLBP subjects (n = 25) were challenged to unexpected and expected perturbations on stable and unstable surfaces. 'Tampa scale for kinesiophobia - Adjusted version-13' was used to measure kinesiophobia. Regression analysis revealed significant negative correlation between kinesiophobia scores and voluntary responses of rectus abdominis (RA) for unexpected perturbations on stable (r = -0.69, 95% of CI: -0.85 to -0.40, p < 0.000, r(2) = 0.41) and unstable surfaces (r = -0.47, 95% of CI: -0.72 to -0.09, p < 0.018, r(2) = 0.29). The activity of erector spinae was not influenced by most of testing conditions in the study except task on unstable surface for expected perturbation (r = -0.593, 95% of CI: -0.8 to -0.25, p = 0.002, r(2) = 0.15). RA activity and kinesiophobia score of the CLBP population was significantly inversely associated during anteriorly directed unexpected perturbations. In our study, the significant association between fear of movement and the trunk muscle responses was differentially influenced by expected and unexpected postural demands.

Investigating reduced bag weight as an effective risk mediator for mason tenders

Masonry workers face some of the highest physical demands in the construction industry where large bags of masonry material weighing 42.7 kg are commonly handled by mason tenders who mix the mortar, distribute mortar and bricks/blocks, and erect/dismantle scaffolding throughout the day. The objective of this study was to determine the effectiveness of using half-weight bags (21.4 kg) on reducing the biomechanical loading, physiological response, and perceived exertions. Ten male subjects performed asymmetric lifting tasks simulating unloading bags from a pallet. Muscle activity, trunk kinematics, heart rate, blood pressure and subjective rating data were collected. Spine loads were predicted from a well-validated EMG-assisted model. Bag weight, lift type, bag height at origin, and asymmetry at destination significantly impacted the spine loads. While there was a 50% reduction in bag weight, the peak loads for the half-weight bags were only 25% less than the more available full-weight bags (a reduction of about 320 N of shear and 1000 N of compression). Lifts allowing movement of the feet reduced the loads by about 22% in shear and 27% in compression compared to constrained postures. Interestingly, cumulative spine loads were greater for the lighter bags than the heavy bags ( approximately 40%). The subjective ratings of exertion and risk were significantly lower for the lighter bags. RELEVANCE TO INDUSTRY: The reduction in peak spine loading for the half-weight bags, particularly at the higher heights and when the feet were allowed to move could significantly reduce the injuries of masonry workers. However, there were trade-offs with cumulative loads that may minimize the reduced risk. Overall, given the limited amount of time lifting bags, the reduction of peak loads.

How to lift a box that is too large to fit between the knees

Many studies compared lifting techniques such as stoop and squat lifting. Results thus far show that when lifting a wide load, high back loads result, irrespective of the lifting technique applied. This study compared four lifting techniques in 11 male subjects lifting wide loads. One of these techniques, denoted as the weight lifters' technique (WLT), is characterised by a wide foot placement, moderate knee flexion and a straight but not upright trunk. Net moments were calculated with a 3-D linked segment model and spinal forces with an electromyographic-driven trunk model. When lifting the wide box at handles that allow a high grip position, the WLT resulted in over 20% lower compression forces than the free, squat and stoop lifting technique, mainly due to a smaller horizontal distance between the l5S1 joint and the load. When lifting the wide box at the bottom, none of the lifting techniques was clearly superior to the others. STATEMENT OF RELEVANCE: Lifting low-lying and large objects results in high back loads and may therefore result in a high risk of developing low back pain. This study compares the utility of a WLT, in terms of back load and lumbar flexion, to more familiar techniques in these high-risk lifting tasks.

Validation of Revised NIOSH Lifting Equation and 3D SSP Model to Predict Risk of Work-Related Low Back Pain

This study is based upon data collected for a large scale, multi-site prospective cohort study of work-related low back pain (WLBP). The aim of this study was to validate the Revised NIOSH Lifting Equation (RNLE) and the 3D Static Strength Prediction Model (3D SSPM) to predict the risk of WLBP. Complete baseline and follow up data on job physical exposure and WLBP status were available on 258 workers free of WLBP at baseline. Relationships between job physical factors and incident cases of WLBP were analyzed using the Cox proportional hazards model. There was evidence of association between load moment and the Lifting Index calculated from the RNLE and incidence of WLBP, and no evidence of association with estimated compressive force on L5/S1 disc and percent capable population. It is concluded that the RNLE is predictive of future risk of WLBP.

Continuous assessment of low back loads in long-term care nurses

Considerable effort has been spent evaluating aspects of low back injury risk in nursing yet comprehensive evaluation of all work tasks has been limited. The purpose of this study was to evaluate peak and cumulative lumbar spine loads experienced by personal support workers. A total of 20 female long-term care workers were observed and had trunk posture monitored via an inclinometer throughout their shift. When adjusted for an 8-h workday, workers experienced cumulative loads of 21.3 +/- 4.6 MNs, 1.8 +/- 0.6 MNs and 2.9 +/- 1.4 MNs for compression, lateral and anterior shear, respectively. Patient care, unloaded standing, walking and miscellaneous tasks accounted for almost 80% of cumulative compression, while lifts and transfers accounted for less than 10%. Mechanical lift assists reduced peak loads and contributed minimally to cumulative loading. These findings suggest that both peak and cumulative spine loads should be considered when evaluating injury risk in the nursing profession. STATEMENT OF RELEVANCE: This study has shown that tasks other than patient transfers and lifts are important in the assessment of low back injury risk in nurses. The method developed is a relatively straightforward approach that can be used to estimate peak and cumulative spine load to provide insight to risk of injury in many occupational settings.

Effects of Anterior Shear Displacement Rate on the Structural Properties of the Porcine Cervical Spine

While the individual tissues of the vertebral joint demonstrate viscoelastic properties, the global viscoelastic properties of the lumbar vertebral joint are not well established. This study investigated how changes in displacement rate influenced the mechanical response of the porcine cervical spine (a surrogate or model for the human lumbar spine) exposed to acute anterior shear failure loading. Thirty porcine cervical spine specimens (15 C3-C4 and 15 C5-C6) were placed under a 1600 N compressive load and subsequently loaded in anterior shear to failure at one of three randomly assigned displacement rates (1 mm/s, 4 mm/s, or 16 mm/s). Ultimate anterior shear force, ultimate displacement, average stiffness, and energy stored until failure were calculated. Load rate in the elastic region was also calculated to compare the load rates used in this study to those used in previous studies. Changes in displacement rate affected the C3-C4 and C5-C6 specimens differently. C5-C6 specimens tested at 16 mm/s had an ultimate force that was 28% and 23% higher than at 1 (p=0.0215) and 4 mm/s (p=0.0461), respectively. The average stiffness to failure of the C5-C6 specimens tested at 16 mm/s was 52% higher than at 4 mm/s (p=0.0289). No such differences were found for the C3-C4 specimens. An increase in the anterior shear displacement rate did not necessarily demonstrate viscoelasticity of the vertebral joint. Specimen intervertebral levels were affected differently by changes in anterior shear displacement rate, which may have been a result of anatomical and postural differences between the two levels. Future studies should further investigate the effect of displacement rate on the spine and the inconsistencies between different specimen levels.

Comparison of two heights for forward-placed trunk support with standing work

Two forward-placed supports with different heights are investigated using human motion capture and EMG. Ten male participants stood in 10 degrees increments of trunk flexion between 0 and 40 degrees for three conditions; leaning on a desk adjusted to the height of the pelvis, leaning on a prototype support at the height of the sternum and with no external support. Low back and hip extensor muscle activity was reduced by an average 60% with leaning against the prototype compared to the no-support condition whereas leaning on a desk produced no significant change in muscle activity. Supported conditions resulted in greater forward displacement of the trunk by at least two-fold compared to no-support representing a longer reach distance. No adverse changes in kinematics indicate that either support blocked segmental flexion of the pelvis, lumbar spine or thoracic spine. These findings suggest that leaning against a higher-placed trunk support could be beneficial for tasks requiring forward flexion.

Evaluation of three ergonomic measures on productivity, physical work demands, and workload in gypsum bricklayers

BACKGROUND

This study evaluated the effects of a combination of three ergonomic measures designed to reduce the risk of low back complaints among gypsum bricklayers. The measures focused on optimizing working height and reducing carrying distances.

METHODS

A within-subjects (N = 10) controlled field study was used to compare the effects of working with the ergonomic measures with those of working with conventional working methods at the worksite during the course of a full working day. Productivity, work demands, and workload were assessed.

RESULTS

No effects were found on productivity, total work time, duration of tasks, duration of carrying, or energetic or biomechanical workload. However, the duration and frequency of working between knee and hip height during a working day increased by 25% and 15%, respectively, due to the ergonomic measures. During the finishing task, the duration and frequency of working below knee level decreased significantly by 4 min and 71 times, respectively.

CONCLUSION

The limited impact of the ergonomic measures argues for additional measures to reduce the risk of low back complaints.

Validity of estimates of spinal compression forces obtained from worksite measurements

Estimates of peak spinal compression in manual materials handling were compared between a state-of-the-art laboratory technique and a method applicable at the worksite. Nine experienced masons performed seven simulated tasks in a mock-up in the laboratory and nine matched masons were studied during actual performance of the same tasks at the worksite. From kinematic and kinetic data obtained in the laboratory, compression forces on the L5S1 joint were calculated. In addition, compression forces were estimated from the horizontal and vertical position of the blocks handled relative to the subject measured at the worksite. Comparison of group-averaged values showed that the worksite method underestimated peak compression by about 20%. Rank ordering of tasks for back load was, however, consistent between methods, supporting validity of the worksite method to compare different tasks or to determine the effects of ergonomic interventions with regard to mechanical back load. STATEMENT OF RELEVANCE: This study validated a method that can be used by ergonomists to determine the effects of (characteristics of) manual materials handling tasks on back load at the worksite.

Using observation and self-report to predict mean, 90th percentile, and cumulative low back muscle activity in heavy industry workers

Occupational injury research depends on the ability to accurately assess workplace exposures for large numbers of workers. This study used mixed modeling to identify observed and self-reported predictors of mean, 90th percentile, and cumulative low back muscle activity to help researchers efficiently assess physical exposures in epidemiological studies. Full-shift low back electromyography (EMG) was measured for 133 worker-days in heavy industry. Additionally, full-shift, 1-min interval work-sampling observations and post-shift interviews assessed exposure to work tasks, trunk postures, and manual materials handling. Data were also collected on demographic and job variables. Regression models using observed variables predicted 31-47% of the variability in the EMG activity measures, while self-reported variables predicted 21-36%. Observation-based models performed better than self-report-based models and may provide an alternative to direct measurement of back injury risk factors.

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.

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.

Breath control during manual free-style lifting of a maximally tolerated load

Clear evidence links voluntary breath control, intra-abdominal pressure and lumbar stability. However, little is known regarding optimal breath control during manual materials handling. No studies have examined natural breath control while lifting a maximal load. Fourteen healthy subjects lifted a loaded crate from the floor to a table while respiratory flow data were collected. The loads lifted began at 10% of body weight and increased up to 50% (if tolerated) by 5% increments. Data from the minimum, moderate and maximum loads were analysed. Uniform and consistent breath holding during lifting of a maximally tolerated load did not occur. Across all three loads, frequency of inspiration was highest immediately prior to lift-off and significantly higher inspired volume occurred at lift-off of the load compared with preparation for lifting. Holding the breath does not appear to be related to lifting of a maximally tolerated load from floor to table. STATEMENT OF RELEVANCE: The findings demonstrate that consistent patterns of naturally occurring breath control during lifting of a maximal load can be identified and do not include uniform breath holding. The findings may assist in creating models for optimal breath control, which will minimise risk of injury during manual material handling tasks.

The ability of limited exposure sampling to detect effects of interventions that reduce the occurrence of pronounced trunk inclination

Ergonomics interventions often focus on reducing exposure in those parts of the job having the highest exposure levels, while leaving other parts unattended. A successful intervention will thus change the form of the job exposure distribution. This disqualifies standard methods for assessing the ability of various exposure measurement strategies to correctly detect an intervention's effect on the overall job exposure of an individual worker, in particular for the safety or ergonomics practitioner who with limited resources can only collect a few measurements. This study used a non-parametric simulation procedure to evaluate the relationship between the number of measurements collected during a self-paced manufacturing job undergoing ergonomics interventions of varying effectiveness, and the probability of correctly determining whether and to which extent the interventions reduced the overall occurrence of pronounced trunk inclination, defined as an inclination of at least 20 degrees . Sixteen video-recordings taken at random times on multiple days for each of three workers were used to estimate the time distribution of each worker's exposure to pronounced trunk inclination. Nine hypothetical ergonomics intervention scenarios were simulated, in which the occurrence of pronounced trunk inclination in the upper 1/8, 1/4, and 1/2 of the job exposure distribution was reduced by 10%, 30% and 50%. Ten exposure measurement strategies were explored, collecting from one to ten pre- and post-intervention exposure samples from an individual worker. For each worker, intervention scenario and sampling strategy, data were bootstrapped from the measured (pre-intervention) and simulated (post-intervention) exposure distributions to generate empirical distributions of the estimated intervention effect. Results showed that for the one to three intervention scenarios that had the greatest effect on the overall occurrence of trunk inclination in the job, one to four pre- and post-intervention measurements, depending on worker, were sufficient to reach an 80% probability of detecting that the intervention did, indeed, have an effect. However, even for the intervention scenario that had the greatest effect on job exposure, seven or more samples were needed for two of the three workers to obtain a probability larger than 50% of estimating the magnitude of the intervention effect to within +/-50% of its true size. For almost all interventions affecting 1/8 or 1/4 of the job, limited exposure sampling led to low probabilities of detecting any intervention effect, let alone its correct size.

Trunk postures and peak and cumulative low back kinetics during upright posture sheep shearing

Sheep shearing is the most demanding occupation in the wool harvesting industry and is known to have a high prevalence of low back pain. While use of a commercially available trunk harness reduces load on the low back, the extreme trunk flexion associated with shearing still remains. A novel, upright posture shearing technique has been designed to allow a more neutral spine posture. This study assessed this upright technique and found significant reductions in both trunk flexion and cumulative low back loading when compared to either the traditional method or the use of the trunk harness. Moments about the shoulder tended to be higher while using the upright shearing technique and further investigation of shoulder kinetics will be required to assess whether this creates injury risk to the upper extremity. Despite increased shoulder moments, the reduction in flexion and cumulative loading with the use of the upright technique has the potential to reduce risk of low back pain among shearers.

Developing an estimate of daily cumulative loading for the knee: examining test-retest reliability

Although the knee adduction moment during gait is a valid and reliable proxy for the dynamic load on the medial compartment of the knee, it represents exposure to loading during one stride only. In contrast, a measure that incorporates both the nature and frequency of loading throughout daily activities might provide additional insight into the effects of cumulative knee loading. The purpose of this study was to introduce a new representation of daily cumulative knee loading and examine its test-retest reliability. Thirty healthy adults participated. Cumulative knee loading was calculated on two testing periods from the mean external knee adduction moment stance phase impulse, measured with a three-dimensional motion capture system over five walking trials, and mean steps/day, measured with a unidimensional accelerometer over one week. Analysis for test-retest reliability included Bland-Altman graphs, intraclass correlation coefficients (ICC 2,1) and standard errors of measurements (SEM). The ICC values for cumulative knee loading, adduction impulse and steps/day ranged from 0.84 to 0.89. Bland-Altman plots suggested daily cumulative knee loading and steps/day measures were less reliable at higher values. The SEM values were 9.67 kNm s, 1.45 Nm s and 1043 steps/day for cumulative knee loading, adduction impulse and steps/day, respectively. Daily cumulative knee loading is reliable and provides a stable measure of the total exposure to knee loading. These findings support further study of cumulative knee loading to determine its potential clinical importance.

Effectiveness of an on-body lifting aid at reducing low back physical demands during an automotive assembly task: assessment of EMG response and user acceptability

The purpose of this study was to investigate the effectiveness and user acceptability of a Personal Lift-Assist Device (PLAD) at an automotive manufacturing facility, with operators who perform an on-line assembly process requiring forward bending and static holding. Surface EMG data were collected at six sites on the low back and abdomen, and an accelerometer was used to measure trunk inclination. Use of the PLAD significantly reduced the thoracic and lumbar erector spinae activity and EMG-predicted compression at the 10th, 50th, and 90th APDF percentile levels (p < or = 0.05), without significantly increasing rectus abdominus activity or trunk flexion. Similarly, ratings of perceived exertion were found to be significantly lower when wearing the PLAD (p = 0.006). Subjective opinions were positive, with 8/10 subjects indicating they would wear the device everyday. With slight changes, workers felt that the PLAD could be beneficial at reducing forces and discomfort in similar industrial or manual materials handling tasks that place excessive physical demands on the low back.

Working height, block mass and one- vs. two-handed block handling: the contribution to low back and shoulder loading during masonry work

The goal of this study was to compare the effects of the task variables block mass, working height and one- vs. two-handed block handling on low back and shoulder loading during masonry work. In a mock-up of a masonry work site, nine masonry workers performed one- and two-handed block-lifting and block-placing tasks at varying heights (ranging from floor to shoulder level) with blocks of varying mass (ranging from 6 to 16 kg). Kinematics and ground reaction forces were measured and used in a 3-D linked segment model to calculate low back and shoulder loading. Increasing lifting height appeared to be the most effective way to reduce low back loading. However, working at shoulder level resulted in relatively high shoulder loading. Therefore, it was recommended to organise masonry work in such a way that blocks are handled with the hands at about iliac crest height as much as possible.

Determining the optimal size for posture categories used in video-based posture assessment methods

Currently, there are no standards for the development of posture classification systems used in observation-based ergonomic posture assessment methods. This study was conducted to determine if an optimal posture category size for different body segments and posture views could be established by examining the trade-off between magnitude of error and the number of posture category misclassification errors made. Three groups (trunk flexion/extension and lateral bend; shoulder flexion/extension and adduction/abduction; elbow flexion/extension) of 30 participants each selected postures they perceived to correctly represent the video image shown on a computer screen. For each view, 10 images were presented for five different posture category sizes, three times each. The optimal posture category sizes established were 30 degrees for trunk, shoulder and elbow flexion/extension, 30 degrees for shoulder adduction/abduction and 15 degrees for trunk lateral bend, suggesting that posture category size should be based on the body segment and view of the image being assessed. Across all conditions, the posture category sizes were comparable to those used in published ergonomic tools.

The use of ergonomic measures and musculoskeletal complaints among carpenters and pavers in a 4.5-year follow-up study

The primary aim of this follow-up study was to evaluate the association between the use of ergonomic measures and musculoskeletal complaints among construction workers during an informational campaign on sector level. A questionnaire was sent twice to a cohort of 914 Dutch carpenters and pavers, once in 2000 and once in 2005. Relative risks (RR) were calculated for the regular use of ergonomic measures and regular or sustained lower back and shoulder pain among workers at baseline and 4.5 years follow-up. The response percentages were 78% (n = 469) for carpenters and 64% (n = 202) for pavers. Regular use of specific ergonomic measures varied from 15-66% at baseline to 17-66% at follow-up. Four specific ergonomic measures showed a statistically significant increase in usage. Regular or sustained lower back and shoulder complaints among carpenters decreased from 38 to 34% (p = 0.07) and 24 to 22% (p = 0.18), respectively. Among pavers, lower back (34%) and shoulder (17 to 18%) complaints remained the same or increased. Regular use of a height-adjustable working platform was associated with a lower likelihood of shoulder complaints at baseline (RR = 0.68; 95% CI: 0.46-<1.00) and low back complaints at follow-up (RR = 0.66; 95% CI: 0.50-0.88) among carpenters. Also regular use of aids for handling heavy loads was associated with no shoulder complaints at baseline RR = 0.62 (95% CI: 0.40-0.97) among carpenters. In conclusion, despite a large informational campaign, regular use of ergonomic measures remained low in a 4.5 year period. Regular use of the majority of ergonomic measures was associated, although not statistically significantly, with a lower likelihood of lower back or shoulder complaints. It is recommended to select, apply and monitor powerful implementation strategies to ensure the use of effective ergonomic measures at construction sites.

Intervertebral disc segmentation and volumetric reconstruction from peripheral quantitative computed tomography imaging

An automatic system for segmenting and constructing volumetric representations of excised intervertebral discs from peripheral quantitative computed tomography (PQCT) imagery is presented. The system is designed to allow for automatic quantitative analysis of progressive herniation damage to the intervertebral discs under flexion/extension motions combined with a compressive load. Automatic segmentation and volumetric reconstruction of intervertebral disc from PQCT imagery is a very challenging problem due to factors such as streak artifacts and unclear material density separation between contrasted intervertebral disc and surrounding bone in the PQCT imagery, as well as the formation of multiple contrasted regions under axial scans. To address these factors, a novel multiscale level set approach based on the Mumford-Shah energy functional in iterative bilateral scale space is employed to segment the intervertebral disc regions from the PQCT imagery. A Delaunay triangulation is then performed based on the set of points associated with the intervertebral disc regions to construct the volumetric representation of the intervertebral disc. Experimental results show that the proposed system achieves segmentation and volumetric reconstructions of intervertebral discs with mean absolute distance error below 0.8 mm when compared to ground truth measurements. The proposed system is currently in operational use as a visualization tool for studying progressive intervertebral disc damage.

Development and evaluation of an observational Back-Exposure Sampling Tool (Back-EST) for work-related back injury risk factors

We developed and evaluated an observational Back-Exposure Sampling Tool. A literature review suggested 53 exposure variables; these were reduced to 20 following field trials. Kappas for agreement beyond chance between six observers assessing exposures in 72 photos ranged from 0.21 to 1.0, with the highest values for posture type, trunk angle, manual materials handling, hands on item, and load weight. Intraclass correlations for agreement between pairs observing 17 workers once per minute for a full-shift were >0.74 for most postural, trunk angle, and manual materials handling variables. In validity testing, the proportions of shifts in flexion/extension and lateral bending observed for 169 full-shifts were compared to inclinometer measurements. Pearson correlations were 0.42 for 45-60 degrees flexion and 0.9 for >60 degrees flexion, but only 0.11-0.19 for lateral bending and trunk flexion less than 45 degrees . When lower flexion angles were collapsed to include trunk extension, correlations increased to >0.5.

The role of dynamic flexion in spine injury is altered by increasing dynamic load magnitude

BACKGROUND

Evidence indicates that loads and postures that an individual is exposed to alter their risk of reporting low back pain or incurring a spine injury. In vitro research indicates cyclic flexion under static compressive loads can lead to disc herniation, while repetitive compression in neutral or flexed postures leads to vertebral failure. However, no research has examined the likelihood of altering injury site (disc vs. bone) when dynamic load exposures are varied concurrently with cyclic flexion.

METHODS

Fifty porcine cervical spinal units were assigned to one of five groups based on peak normalized loads of 10%, 30%, 50%, 70% and 90% of the unit's predicted tolerance. Specimens underwent passive range of motion tests to determine individualized range of motion. Once individualized loads and angles were determined, specimens were cyclically compressed and flexed based on profiles obtained from a floor to waist height lift until failure occurred or 12h elapsed. After testing specimens were dissected to identify injury site, and cumulative exposures sustained to failure were calculated.

FINDINGS

Disc injury was not observed when peak loads exceeded 30% of the tolerance, while they comprised a higher percentage of the total injuries incurred when decreasing from the 30% to 10% groups. Those specimens exhibiting disc injury tolerated significantly greater: cycles to failure (9000 vs. 930, P<0.0001), cumulative compression (10872.7 vs. 1089.5MNs, P<0.001), shear (1822.1 vs. 150.6MNs, P<0.001) and angular excursion (130809.7 degrees vs. 12714.7 degrees , P<0.001).

INTERPRETATION

If the spine is exposed to greater levels of load, in the presence of repetitive flexion, it is more likely to experience vertebral fracture. However, if the spine is exposed to many cycles of low peak loads, injury is more likely to occur to the intervertebral disc than to the vertebral bone or endplate.

Quantifying relationships between selected work-related risk factors and back pain: a systematic review of objective biomechanical measures and cost-related health outcomes

The objective of this investigation was to use published literature to demonstrate that specific changes in workplace biomechanical exposure levels can predict reductions in back injuries. A systematic literature review was conducted to identify epidemiologic studies which could be used to quantify relationships between several well-recognized biomechanical measures of back stress and economically relevant outcome measures. Eighteen publications, describing 15 research studies, which fulfilled search criteria were found. Quantitative associations were observed between back injuries and measures of spinal compression, lifting, lifting ratios, postures, and combinations thereof. Results were intended to provide safety practitioners with information that could be applied to their own work situations to estimate costs and benefits of ergonomic intervention strategies before they are implemented.

Applications of biomechanics for prevention of work-related musculoskeletal disorders

This paper summarises applications of biomechanical principles and models in industry to control musculoskeletal disorders of the low back and upper extremity. Applications of 2-D and 3-D biomechanical models to estimate compressive force on the low back, the strength requirements of jobs, application of guidelines for overhead work and application of strain index and threshold limit value to address distal upper extremity musculoskeletal disorders are presented. Several case studies applied in the railroad industry, manufacturing, healthcare and warehousing are presented. Finally, future developments needed for improved biomechanical applications in industry are discussed. The information presented will be of value to practising ergonomists to recognise how biomechanics has played a significant role in identifying causes of musculoskeletal disorders and controlling them in the workplace. In particular, the information presented will help practising ergonomists with how physical stresses can be objectively quantified.

Evolving ergonomics?

The theme developed in this position paper follows the current evolution of injury prevention in the backs of workers. Job change or 'fitting the task to the person' has come far, but will probably not result in zero injury rates. This is because the cause of injury is heavily influenced by the way that a worker moves. A review of injury mechanisms reveals the need for the biomechanist/ergonomist to incorporate features in biomechanical models that recognise these injury mechanisms. The implication of one such model is that the next leap toward a zero injury rate may be approached with 'fitting the person to the task' or at least retraining the way that workers move. A few examples of movement-based back injury prevention strategies are provided. Finally, some thoughts on implementing such an approach are expressed. This is a review and position paper written in honour of Professor Don Chaffin's career.

National occupational research agenda (NORA) future directions in occupational musculoskeletal disorder health research

Musculoskeletal disorders are among the most costly health care problems facing society today. The scientific literature has indicated that psychosocial factors, individual factors, workplace physical requirements, and workplace organizational factors have been associated with risk. Since musculoskeletal risk is multi-dimensional, the magnitude of risk attributable to various factors can be of importance to scientists and policy makers in designing countermeasures to reduce injury incidence. Traditionally, the disciplines of biomechanics, physiology, and psychophysics have dominated the body of knowledge that has defined exposure limitations to work. However, recent research has explored the association of psychosocial and work organization factors with musculoskeletal problems. Advances have been made to better quantify the levels of occupational exposure by improved exposure metrics, quantification of three-dimensional loads experienced by certain joints (e.g. the spine), identification of tissue tolerance limits and tissue response to mechanical stresses, and the impact of psychosocial stresses. However, efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies. Although we are beginning to understand how the major risk factors influence the load-tolerance relationship of human tissue, how these risk factors interact is virtually unexplored. Since the impact of the interactions may be far greater than that of any individual factor, the impact of the interactions between risk factors must be delineated so that work-related risk can be better quantified. Efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies.

Does the asymmetry multiplier in the 1991 NIOSH lifting equation adequately control the biomechanical loading of the spine?

The aim of this research was to evaluate whether the asymmetry multiplier incorporated in the 1991 National Institute for Occupational Safety and Health lifting equation adequately controls the biomechanical spine loads during asymmetric lifting. Sixteen male subjects lifted a box from four initial locations varying in terms of the angular deviation from the mid-sagittal plane (0, 30, 60 and 90 degrees). From each location, boxes that weighed the recommended weight limit (RWL) and three times the RWL were lifted at two qualitatively defined lifting speeds. Ground reaction forces were combined with kinematic data in a linked-segment model to quantify the 3-D moments at the base of the spine (L5/S1) and the spine compression forces. The results show that the twisting and lateral bending moments increased with task asymmetry despite the lessening of the RWL (p<0.01). The flexion moment and the spine compression decreased with asymmetry, although at a slower rate than the RWL. When the dynamics were removed from the linked segment spine model to approximate the assumption of slow and smooth lifting, the estimated compression remained approximately 3400 N across all asymmetry conditions. Thus, the reduction in the RWL due to asymmetry multiplier appears appropriate and should not be changed, as been suggested by recent psychophysical studies.

Low-back loading in lifting two loads beside the body compared to lifting one load in front of the body

Low-back load during manual lifting is considered an important risk factor for the occurrence of low-back pain. Splitting a load, so it can be lifted beside the body (one load in each hand), instead of in front of the body, can be expected to reduce low-back load. Twelve healthy young men lifted 10 and 20-kg wide and narrow loads in front of the body (the single-load lifts). These single-load lifts were compared to a lifting condition in which two 10-kg loads (a total of 20 kg) were lifted beside the body (the split-load lift). Lifts were performed from an initial hand height of 29 cm with four different lifting techniques (stoop, squat, straddle and kneeling techniques). Using measured kinematics, ground reaction forces, and electromyography, low-back loading (3D net moments and spinal forces at the L5/S1 joint) was estimated. Lifting a 20-kg split-load instead of a 20-kg single-load resulted in most cases in a reduction (8-32%) of peak L5/S1 compression forces. The magnitude of the reduction was roughly comparable to halving the load mass and depended on lifting technique and load width. The effects of load-splitting could largely be explained by changes in horizontal distance between the load and L5/S1.