Inter- and intra-observer reliability of calculating cumulative lumbar spine loads

The aim of this study was to quantify the precision of manual video digitization of three typical industrial tasks, as evaluated by the comparison of four cumulative kinetic parameters at the L4/L5 intervertebral joint: compression, joint shear, reaction shear and moment. Ten observers were recruited (five male and five female), with an undergraduate background in human anatomy. On each of three test days, each observer digitized five repeats of each of three typical industrial lifting tasks of 5 to 6 s in duration. A rigid link segment model that incorporated a single muscle equivalent model was used to calculate the cumulative loading based on the digitized coordinates. Inter-observer reliability was assessed using a mixed model ANOVA, and no significant differences were found to result from observer, gender, day or trial. Intraclass correlation coefficients (ICC) were calculated within each task to quantify intra-observer reliability. Overall, the ICCs were excellent (>0.75), with the exception of moderate values for reaction shear for Tasks 2 and 3. Compression and moment demonstrated the highest reliability of the four parameters studied, which is beneficial from an ergonomic standpoint, as compression is the most commonly used parameter for job assessments. This study demonstrated manual video digitization to be a reliable tool for the quantification of cumulative spinal loading, both within a given observer, and across days, trials and observers.     

An evaluation of predictive methods for estimating cumulative spinal loading

The focus of this study was to assess the amount of error present in several approaches that have been commonly used to estimate the cumulative spinal loading during manual materials handling tasks. Three male subjects performed three sagittal plane lifting tasks of varying loads and postural requirements. Video recordings of the tasks were digitized and a biomechanical model was used to calculate the spinal loading (compression, joint shear, reaction shear, and flexion/extension moment) at L4/L5 for each frame of data. The 'gold standard' for cumulative loading experienced by the subjects was obtained by integrating the resultant biomechanical model outputs for the entire lifting cycle. Five approaches that quantify cumulative spinal loading, four that use discrete measures and one that reduces the number of frames used (5 Hz), were used and compared with the gold standard. The four methods using discrete measures to quantify the cumulative demands of a task resulted in substantial errors (average error across task and subjects was 27-69%). Reducing the number of frames of data processed to 5 frames/s preserved the time varying information and was the only approach examined that did not induce significant error into the cumulative loading estimates. This study indicates that errors in cumulative spinal loading estimates can be large depending upon the approach used, which will hinder any progress in developing a dose-response link between cumulative exposure and an increased risk of low-back pain or injury.     

An evaluation of predictive methods for estimating cumulative spinal loading

The focus of this study was to assess the amount of error present in several approaches that have been commonly used to estimate the cumulative spinal loading during manual materials handling tasks. Three male subjects performed three sagittal plane lifting tasks of varying loads and postural requirements. Video recordings of the tasks were digitized and a biomechanical model was used to calculate the spinal loading (compression, joint shear, reaction shear, and flexion/extension moment) at L4/L5 for each frame of data. The ‘gold standard’ for cumulative loading experienced by the subjects was obtained by integrating the resultant biomechanical model outputs for the entire lifting cycle. Five approaches that quantify cumulative spinal loading, four that use discrete measures and one that reduces the number of frames used (5 Hz), were used and compared with the gold standard. The four methods using discrete measures to quantify the cumulative demands of a task resulted in substantial errors (average error across task and subjects was 27–69%). Reducing the number of frames of data processed to 5 frames/s preserved the time varying information and was the only approach examined that did not induce significant error into the cumulative loading estimates. This study indicates that errors in cumulative spinal loading estimates can be large depending upon the approach used, which will hinder any progress in developing a dose-response link between cumulative exposure and an increased risk of low-back pain or injury.     

The assessment of material handling strategies in dealing with sudden loading: The effects of load handling position on trunk biomechanics

Back injury caused by sudden loading is a significant risk among workers that perform manual handling tasks. The present study investigated the effects of load handling position on trunk biomechanics (flexion angle, L5/S1 joint moment and compression force) during sudden loading. Eleven subjects were exposed to a 6.8 kg sudden loading while standing upright, facing forward and holding load at three different vertical heights in the sagittal plane or 45° left to the sagittal plane (created by arm rotation). Results showed that the increase of load holding height significantly elevated the peak L5/S1 joint compression force and reduced the magnitude of trunk flexion. Further, experiencing sudden loading from an asymmetric direction resulted in significantly smaller peak L5/S1 joint compression force, trunk flexion angle and L5/S1 joint moment than a symmetric posture. These findings suggest that handling loads in a lower position could work as a protective strategy during sudden loading.     

A validation of a posture matching approach for the determination of 3D cumulative back loads

The purpose of this project was to investigate the amount of error in calculating cumulative lumbar spine kinetics using a posture matching approach (3DMatch) compared to a 3D coordinate electromagnetic tracking approach (FASTRAK). Six subjects were required to perform five repeats each of two symmetrical and two asymmetrical lifts while being simultaneously recorded from 4 camera views at viewing angles of 0 degrees , 45 degrees , 60 degrees and 90 degrees to the sagittal plane while wearing eight FASTRAK sensors to define an 8 segment rigid link model (RLM) of the head, arms, and trunk. Four hundred and eighty lifts (6 subjects x20 lifts x4 camera views) were analyzed using the 3DMatch posture-matching program to calculate the following cumulative loads at the L4/L5 joint: compression, anterior shear, posterior shear, reaction shear and extension moment. The errors in cumulative load calculation were determined as the difference between the values calculated for the same lifts using a 3D RLM that used electromagnetic motion tracking sensors (FASTRAK) positioned at the segment center of masses as model inputs. No significant difference (p<0.05) in the relative error for any of the cumulative loading variables between the four camera views and the 3D RLM approach was found. Furthermore the relative errors for cumulative compression, joint anterior shear, reaction anterior shear and extension moment were all below 12%. These results suggest that posture matching by trained users can provide reasonable 3D data to calculate cumulative low back loads with a biomechanical model.     

The effect of camera viewing angle on posture assessment repeatability and cumulative spinal loading

Video-based task analysis in the workplace is often limited by equipment location and production line arrangement, therefore making it difficult to capture the motion in a single plane. The purpose of this study was to investigate the effects of camera placement on an observer's ability to accurately assess working postures in three dimensions and the resultant influence on the reliability and repeatability of calculated cumulative loading variables. Four video cameras were placed at viewing angles of 0 degrees, 45 degrees, 60 degrees and 90 degrees to the frontal plane, enabling the simultaneous collection of views of four lifting tasks (two symmetric and two asymmetric). A total of 11 participants were trained in the use of the 3DMatch 3-D posture matching software package (developed at the University of Waterloo) and were required to analyse 16 lifting trials. Four of the participants were randomly selected to return within 72 h and repeat the analysis protocol to test intra-observer repeatability. Posture matching agreement between camera views was higher when the body segments had a minimal range of motion during the task. There was no significant participant main effect; however, there was a significant (p < 0.05) task main effect. Intraclass correlation coefficients (ICC) were calculated to assess the between day reliability. Compression, reaction anterior shear and extension moment were all found to have excellent reliability (ICC > 0.75). Joint anterior shear and joint posterior shear both provided fair to good reliability (0.4 > ICC < 0.75). Overall, the impact of the camera viewing angle on an observer's ability to match working postural exposure was found to be small.     

The accuracy of self-report and trained observer methods for obtaining estimates of peak load information during industrial work

The purpose of this study was to determine how well self-report (questionnaire=QR) and trained observer (checklist=OBS) data recording methods compared with more expensive video analysis (VID) for estimating various peak physical loading exposure variables on the low backs of 99 employees during work in an automobile assembly plant. The variables studied were L4/L5 spine compression and shear forces, L4/L5 moment, trunk angle, and hand load. Peak low back loads associated with the working postures of, and the applied loads on, each worker were estimated using a 2D biomechanical model that could accommodate inertial forces acting in various directions on the hands independently. Correlations between the VID and OBS methods were greater for each variable than between VID and QR methods, with ranges in coefficients from 0.6 to 0.8, and 0.1 to 0.4, respectively, giving a discouraging impression of the QR, and the OBS method to a lesser degree, for peak low back exposure assessment. Despite the better performance of OBS method for individuals, it was still only able to account for between 36% and 64% of the variance relative to the VID method. When all workers were considered as a single group, compression and shear forces, moment and hand load estimates were the same regardless of method used to collect the data. Self-reported trunk flexion was significantly greater than that reported by trained observers or on video (p<0.0001).Relevance to industryConsiderable time and expense could be saved in large scale studies if it were possible to rely on worker's reports or observation of the physical demands of their jobs instead of traditional video and biomechanical analyses. Assessments of peak exposure of individuals using the self-report and observation methods were discouraging. Analysis of a single group proved more promising, but other groups need to be studied. Interview assisted self-reports may help to improve assessments of individuals and also need to be investigated in the future.     

The effect of camera viewing angle on posture assessment repeatability and cumulative spinal loading

Video-based task analysis in the workplace is often limited by equipment location and production line arrangement, therefore making it difficult to capture the motion in a single plane. The purpose of this study was to investigate the effects of camera placement on an observer's ability to accurately assess working postures in three dimensions and the resultant influence on the reliability and repeatability of calculated cumulative loading variables. Four video cameras were placed at viewing angles of 0°, 45°, 60° and 90° to the frontal plane, enabling the simultaneous collection of views of four lifting tasks (two symmetric and two asymmetric). A total of 11 participants were trained in the use of the 3DMatch 3-D posture matching software package (developed at the University of Waterloo) and were required to analyse 16 lifting trials. Four of the participants were randomly selected to return within 72 h and repeat the analysis protocol to test intra-observer repeatability. Posture matching agreement between camera views was higher when the body segments had a minimal range of motion during the task. There was no significant participant main effect; however, there was a significant (p < 0.05) task main effect. Intraclass correlation coefficients (ICC) were calculated to assess the between day reliability. Compression, reaction anterior shear and extension moment were all found to have excellent reliability (ICC > 0.75). Joint anterior shear and joint posterior shear both provided fair to good reliability (0.4 > ICC < 0.75). Overall, the impact of the camera viewing angle on an observer's ability to match working postural exposure was found to be small.     

A comparison of risk assessment of single and combination manual handling tasks: 3. Biomechanical measures

Anecdotal evidence suggests organisations experience difficulty assessing the risk in manual handling tasks. One reason for this difficulty may be that many common tasks are a combination of lift, lower, push, pull and carry tasks. No prior reports of attempts to assess the risk in combination tasks using biomechanical measures could be found. The aim of the study was to compare the risks assessed in single manual handling tasks with those in combination tasks. Nine male and nine female students performed combination and single handling tasks. The force applied by subjects to a box was recorded and, together with kinematic data on subject posture collected via video, used in a twodimensional dynamic model to estimate the lumbar compression force and lumbar shear force. The hand force, peak lumbar compression force and peak lumbar shear force for each combination task were each compared with the same variable for the single tasks which comprised the combination, using repeated measured analysis of variance with specific contrasts. In at least one of the twelve comparisons performed for each dependent variable, the combination task value was significantly different to the single task value. It is concluded that the risk in combination manual handling tasks can not be accurately assessed by using estimates based on biomechanical measures of single tasks.     

Evaluation and assessment of lumbar load during total shifts for occupational manual materials handling jobs within the Dortmund Lumbar Load Study – DOLLY

The load on the lumbar spine during occupational manual materials handling was previously investigated with respect to short activity sections or to specified load-handling types such as lifting or carrying. Within the so-called Dortmund Lumbar Load Study, analysis of the occupationally induced load on the lumbar spine during total working shifts in the field of surface construction, drop forge, industrial meat processing, and refuse collection was performed on the shop-floor. The body postures adopted, the action forces applied at the hands, and the resultant lumbar load for all load-handling tasks were analysed for 2 shifts in each field on the basis of video evaluations. Via a newly developed detailed classification procedure, the spatial position of the body segments as well as amplitude and direction of the action forces were described in a detailed manner. Consecutive biomechanical model calculations lead, for total shifts, to time courses of various measures for the load on the lumbar spine, such as flexion or torsional moments of force as well as compression and shear forces at the lumbosacral disc. In relation to recommended limits for the maximal disc compression provided in the literature, lumbar load is exceeded in numerous situations during a shift, in particular, with regard to persons of higher age. In a “dose model” applied in this study, the cumulative effect of single-task exposures was considered by superproportional weighting of the compressive force with respect to the corresponding duration of a working task.

Relevance to industry

A comprehensive evaluation of lumbar load for complete shifts is presented considering the real shop-floor conditions. Analyses for dustbin removal, surface construction and industrial meat processing have discovered numerous exceedings of lumbar-load limits. Such tasks should not be performed by older persons from the preventive point of view.     

Estimation of 3-D peak L5/S1 joint moment during asymmetric lifting tasks with cubic spline interpolation of segment Euler angles

Previous research proposed a method using interpolation of the joint angles in key frames extracted from a field-survey video to estimate the dynamic L5/S1 joint loading for symmetric lifting tasks. The advantage of this method is that there is no need to use unwieldy equipment for capturing full body movement for the lifting tasks. The current research extends this method to asymmetric lifting tasks. The results indicate that 4-point cubic spline interpolation of segment Euler angles combined with a biomechanical model can provide a good estimation of 3-D peak L5/S1 joint moments for asymmetric lifting tasks. The average absolute error in the coronal, sagittal, and transverse planes with respect to the local pelvis axes was 16Nm, 22Nm, and 11Nm, respectively. It was also found that the dynamic component of the peak L5/S1 joint moment was not monotonously convergent when the number of interpolation points was increased. These results can be helpful for developing applied ergonomic field-survey tools such as video bases systems for estimating L5/S1 moments of manual materials handling tasks.     

Dynamic biomechanical modelling of symmetric and asymmetric lifting tasks in restricted postures

This article describes investigations of dynamic biomechanical stresses associated with lifting in stooping and kneeling postures. Twelve subjects volunteered to participate in two lifting experiments each having two levels of posture (stooped or kneeling), two levels of lifting height (350 or 700 mm), and three levels of weight (15,20, or 25 kg). One study examined sagitally symmetric lifting, the other examined an asymmetric task. In each study, subjects lifted and lowered a box every 10 s for a period of 2 min in each treatment combination. Electromyography (EMG) of eight trunk muscles was collected during a specified lift. The EMG data, normalized to maximum extension and flexion exertions in each posture, was used to predict compression and shear forces at the L3 level of the lumbar spine. A comparison of symmetric and asymmetric lifting indicated that the average lumbar compression was greater in sagittal plane tasks; however, both anterior-posterior and lateral shear forces acting on the lumbar spine were increased with asymmetric lifts. Analysis of muscle recruitment indicated that the demands of lifting asymmetrically are shifted to ancillary muscles possessing smaller cross-sectional areas, which may be at greater risk of injury during manual materials handling (MMH) tasks. Model estimates indicated increased compression when kneeling, but increased shear forces when stooping. Increasing box weight and lifting height both significantly increased compressive and shear loading on the lumbar spine. A multivariate analysis of variance (MANOVA) indicated complex muscle recruitment schemes—each treatment combination elicited a unique pattern of muscle recruitment. The results of this investigation will help to evaluate safe loads for lifting in these restricted postures.     

Two linear regression models predicting cumulative dynamic L5/S1 joint moment during a range of lifting tasks based on static postures

Previous studies have indicated that cumulative L5/S1 joint load is a potential risk factor for low back pain. The assessment of cumulative L5/S1 joint load during a field study is challenging due to the difficulty of continuously monitoring the dynamic joint load. This study proposes two regression models predicting cumulative dynamic L5/S1 joint moment based on the static L5/S1 joint moment of a lifting task at lift-off and set-down and the lift duration. Twelve men performed lifting tasks at varying lifting ranges and asymmetric angles in a laboratory environment. The cumulative L5/S1 joint moment was calculated from continuous dynamic L5/S1 moments as the reference for comparison. The static L5/S1 joint moments at lift-off and set-down were measured for the two regression models. The prediction error of the cumulative L5/S1 joint moment was 21±14 Nm × s (12% of the measured cumulative L5/S1 joint moment) and 14±9 Nm × s (8%) for the first and the second models, respectively.

Practitioner Summary: The proposed regression models may provide a practical approach for predicting the cumulative dynamic L5/S1 joint loading of a lifting task for field studies since it requires only the lifting duration and the static moments at the lift-off and/or set-down instants of the lift.     

Comparison of measurement methods for quantifying hand force

Hand force is a known risk factor for upper extremity disorders. The objective of the present study was to determine the characteristics of, and the relationships between, exposure assessment methods to quantify hand force. Five methods, used in the laboratory or the field, were used to quantify hand force at three force magnitudes: two direct (or technical) measurement methods, force transducers and electromyography; an observational method; and two self-report approaches, force matching and a visual analogue scale. Five tasks, simulating manual work activities, were performed by 20 participants. The coefficients of variation of measures within and between participants were moderate. All approaches clearly distinguished between the three force levels tested. The reliability of the methods ranged from poor (observation method without information) to good (force transducers method and observation method with information). The measurement methods correlated moderately over all five tasks. Predictions of grip force across all five tasks were poor and even for single tasks the predictions were not much better. The tasks in this study were still simplified; in the field tasks are even more complex and the measurement characteristics might be expected to be less good. A hand force exposure assessment method should therefore be calibrated and tested for each type of hand activity before use.     

Sagittal plane lumbar loading when navigating an obstacle and carrying a load

The current study quantified lumbar loading while carrying an anterior load mass and navigating an obstacle. Eight healthy male participants walked down a walkway and crossed an obstacle under three randomised LOAD conditions; empty-box (2 KG), five kilogram (5 KG) and ten kilogram (10 KG). Each walk was assessed at two events: left foot mid-stance (LMS) and right toe-crossing (TC) to characterise any changes from approach to crossing. Measures of interest included: trunk pitch, L4/L5 joint moment, compression, joint anterior–posterior shear and erector spinae activation. Findings demonstrate that obstacle crossing extended posture by 50, 41, 44%, respectively for each carried load magnitude. Further, these results indicate that shear rather than compressive loading may be an important consideration during crossing due to increase by 8, 9, 22% from LMS to TC for each load magnitude tested. These results provide insight into sagittal lumbar loading when navigating an obstacle while carrying a load.

Practitioner Summary: The risk of carrying while navigating obstacles on the lumbar spine is not completely understood. The forces at the lumbar spine while simultaneously carrying and obstacle crossing were analysed. Data indicate that carrying and obstacle crossing influence lumbar shear loads, thereby moderately increasing the relative risk at lumbar spine.     

Comparison of measurement methods for quantifying hand force

Hand force is a known risk factor for upper extremity disorders. The objective of the present study was to determine the characteristics of, and the relationships between, exposure assessment methods to quantify hand force. Five methods, used in the laboratory or the field, were used to quantify hand force at three force magnitudes: two direct (or technical) measurement methods, force transducers and electromyography; an observational method; and two self-report approaches, force matching and a visual analogue scale. Five tasks, simulating manual work activities, were performed by 20 participants. The coefficients of variation of measures within and between participants were moderate. All approaches clearly distinguished between the three force levels tested. The reliability of the methods ranged from poor (observation method without information) to good (force transducers method and observation method with information). The measurement methods correlated moderately over all five tasks. Predictions of grip force across all five tasks were poor and even for single tasks the predictions were not much better. The tasks in this study were still simplified; in the field tasks are even more complex and the measurement characteristics might be expected to be less good. A hand force exposure assessment method should therefore be calibrated and tested for each type of hand activity before use.     

Biomechanical analysis of peak and cumulative spinal loads during simulated patient-handling activities: a substudy of a randomized controlled trial to prevent lift and transfer injury of health care workers

Back injuries are a serious problem for nursing personnel who perform frequent patient-handling activities. Common prevention strategies include body mechanics education, technique training, and ergonomic interventions such as the introduction of assistive equipment. This investigation assessed and compared the effectiveness of two patient-handling approaches to reducing injury risk. One strategy involved using improved patient-handling technique with existing equipment, and the other approach aimed at eliminating manual patient handling through the use of additional mechanical and other assistive equipment. Both intervention arms received training in back care, patient assessment, and use of the equipment available on their particular wards. An analysis of compliance with interventions and the effects of patient-handling methods on both peak and cumulative spinal compression and shear during various tasks was conducted. Results showed greater compliance with interventions that incorporated new assistive patient-handling equipment, as opposed to those consisting of education and technique training alone. In several tasks, subjects who were untrained or non-compliant with interventions experienced significantly higher peak spinal loading. However, patient-handling tasks conducted with the aid of assistive equipment took substantially longer than those performed manually. This, along with variations in techniques, led to increases in cumulative spinal loading with the use of patient-handling equipment on some tasks. Thus, the use of mechanical assistive devices may not always be the best approach to reducing back injuries in all situations. No single intervention can be recommended; instead all patient-handling tasks should be examined separately to determine which methods maximize reductions in both peak and cumulative lumbar forces during a manoeuver.     

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.     

Prediction accuracy in estimating joint angle trajectories using a video posture coding method for sagittal lifting tasks

This study investigated prediction accuracy of a video posture coding method for lifting joint trajectory estimation. From three filming angles, the coder selected four key snapshots, identified joint angles and then a prediction program estimated the joint trajectories over the course of a lift. Results revealed a limited range of differences of joint angles (elbow, shoulder, hip, knee, ankle) between the manual coding method and the electromagnetic motion tracking system approach. Lifting range significantly affected estimate accuracy for all joints and camcorder filming angle had a significant effect on all joints but the hip. Joint trajectory predictions were more accurate for knuckle-to-shoulder lifts than for floor-to-shoulder or floor-to-knuckle lifts with average root mean square errors (RMSE) of 8.65°, 11.15° and 11.93°, respectively. Accuracy was also greater for the filming angles orthogonal to the participant's sagittal plane (RMSE = 9.97°) as compared to filming angles of 45° (RMSE = 11.01°) or 135° (10.71°). The effects of lifting speed and loading conditions were minimal. To further increase prediction accuracy, improved prediction algorithms and/or better posture matching methods should be investigated.

Statement of Relevance: Observation and classification of postures are common steps in risk assessment of manual materials handling tasks. The ability to accurately predict lifting patterns through video coding can provide ergonomists with greater resolution in characterising or assessing the lifting tasks than evaluation based solely on sampling with a single lifting posture event.     

Noise characteristics of the AVHRR infrared channels

Abstract

Limitations on the precision of digitized data are identified and discussed. Apart from calibration errors, these sources of uncertainty can be divided into three types of noise; digitization, Gaussian and periodic, each of which behaves differently when data is averaged. An attempt is made to separate and quantify these contributions in the infrared channels (3, 4 and 5) of various AVHRR instruments. Typical values of total noise for these channels are also obtained.