Low Back Loading Research Articles

2G1-1 慣性式モーションセンサによる作業中の腰部負担データの蓄積と可視化

2G1-1 慣性式モーションセンサによる作業中の腰部負担データの蓄積と可視化

Supporting the upper body with the hand on the thigh reduces back loading during lifting

When picking objects from the floor, low back pain patients often tend to support the upper body by leaning with one hand on a thigh. While this strategy may reduce back load, this has not yet been assessed, probably due to the difficulty of measuring the forces between hand and thigh.Ten healthy male subjects lifted a pencil and a crate from the floor, with four lifting techniques (free, squat, stoop and a Weight Lifters Technique (WLT)), each of which was performed with and without supporting with one hand on the thigh. A six Degrees of Freedom force transducer, with a comfortable surface to support the hand on, was mounted just above the subject׳s left knee. Hand forces, ground reaction forces, full body kinematics, and trunk EMG were measured. Using inverse dynamics and taking the forces between hand and thigh into account, we calculated 3D L5S1 joint moments, and subsequently estimated spine forces using an EMG-assisted trunk model.For lifting a pencil, hand support reduced average peak total moments by 17–25%, dependent on lifting technique. For crate lifting, hand support reduced total moments by 13–19% compared with one-handed lifting and by 14−26% compared to two-handed lifting. Hand support slightly increased asymmetric motions and caused a substantial increase in asymmetric moments in crate lifting. For compression forces, reductions (up to 28%) were seen in all techniques except in stoop lifts. It is concluded that leaning with a hand on the thigh can lead to substantial reductions of low back loading during lifting.

Efficacy of a trunk orthosis with joints providing resistive force on low-back load in elderly persons during static standing.

PurposePostural alignment of elderly people becomes poor due to aging, possibly leading to low-back pain and spinal deformity. Although there are several interventions for treating these conditions, no previous study has reported the effectiveness of a spinal orthosis or lumbosacral orthosis (LSO) in healthy elderly people without specific spinal deformity. We therefore developed a trunk orthosis to decrease low-back muscle activity while training good postural alignment through resistive force provided by joints with springs (here, called the ORF, which stands for orthosis with joints providing resistive force) as a preventive method against abnormal posture and low-back pain in healthy elderly persons.Patients and methodsFifteen community-dwelling elderly men participated in this study. Participants stood freely for 10 seconds in a laboratory setting under three conditions: without an orthosis, with the ORF, and with an LSO. The Damen corset LSO was selected as it is frequently prescribed for patients with low-back pain. Postural alignment during static standing was recorded using a three-dimensional motion capture system employing infrared cameras. Two force plates were used to record center of pressure. Electromyograms were obtained for bilateral erector spinae (ES), left internal abdominal oblique, and right gluteus medius muscles.ResultsPelvis forward tilt angle tended to increase while wearing the ORF and decrease while wearing the LSO, but these results were not significant compared to no orthosis. Thorax extension angle and thorax angle on pelvis coordinate system significantly increased while wearing the ORF compared to the other two conditions. ES activity significantly decreased while wearing the ORF compared to the other two conditions. Internal oblique activity was significantly smaller while wearing the LSO than with no orthosis. Center of pressure did not significantly differ among the conditions.ConclusionThe ORF significantly improved trunk alignment and decreased ES activity in healthy elderly subjects during static standing.

Detailed assessment of low-back loads may not be worth the effort: A comparison of two methods for exposure-outcome assessment of low-back pain

The trade-off between feasibility and accuracy of measurements of physical exposure at the workplace has often been discussed, but is unsufficiently understood. We therefore explored the effect of two low-back loading measurement tools with different accuracies on exposure estimates and their associations with low-back pain (LBP).Low-back moments of 93 workers were obtained using two methods: a moderately accurate observation-based method and a relatively more accurate video-analysis method. Group-based exposure metrics were assigned to a total of 1131 workers who reported on their LBP status during three follow-up years. The two methods were compared regarding individual and group-based moments and their predictive value for LBP.Differences between the two methods for peak moments were high at the individual level and remained substantial at group level. For cumulative moments, differences between the two methods were attenuated as random inaccuracies cancelled out. Peak moments were not predictive for LBP in any method while cumulative moments were, suggesting comparable predictive values of the two methods. While assessment of low-back load improves from investing in collecting relatively more accurate individual-based data, this does not necessarily lead to better predictive values on a group level, especially not for cumulative loads.

Effects of sitting and standing on upper extremity physical exposures in materials handling tasks

Sitting or standing work configurations modulate musculoskeletal risk. Most existing investigations of these configurations have either studied them separately or lacked focus on the upper extremity, particularly during manual materials handling (MMH) tasks. To address this gap, upper extremity loading in 20 male and 20 females were assessed in 4 MMH tasks in sitting and standing. Differences in electromyographic (EMG) activity, local joint moments and body discomfort between configurations were examined. Interactions between task and sit/stand configuration resulted in increases of up to 500% in joint moments, 94% in EMG activity and 880% in discomfort when tasks were completed while sitting (p < 0.01). Future MMH task designers should consider placing workers in standing postures when feasible to reduce upper extremity loading, but workers should not remain in either configuration for extended periods of time as the negative effects of both workspace geometries can instigate future musculoskeletal disorders.Practitioner Summary: Sitting and standing modify occupational musculoskeletal risk. We examined how performing identical tasks while sitting or standing altered upper extremity and low back loading. In general, sitting increased muscle activity and discomfort, while standing increased local joint moments. The benefits of standing outweighed those of sitting across the range of tasks.

The effects of operator position, pallet orientation, and palletizing condition on low back loads in manual bag palletizing operations

Many mining commodities are packaged and shipped using bags. Small bags are typically loaded onto pallets for transport and require a significant amount of manual handling by workers. This specific task of manual bag handling has been associated with the development of musculoskeletal disorders (MSDs), especially low back disorders. This study evaluates the biomechanical demands of different work layouts when performing manual palletizing of small bags, and evaluates the biomechanical stresses associated with different stacking techniques. Results indicate that peak forward bending moments as well as spinal compression and shear forces are higher when the pallet is situated at the side of the conveyor as opposed to the end of the conveyor. At low levels of the pallet, controlled bag placement results in higher peak forward bending moments than stacking at higher levels and when dropping the bag to lower levels. The results of this study will be used to inform the development of an audit tool for bagging operations in the mining industry. Relevance to industryIn many cases for workers loading small bags, compression forces exceed the NIOSH criterion of 3400 N. Orientation of the pallet has a significant impact on spinal compression, and positioning the pallet at the end of the conveyor reduces the estimated compressive loading on the lumbar spine by approximately 800 N.

Using Peak Vicon data to drive Classic JACK animation for the comparison of low back loads experienced during para-rowing

The use of kinematic data collected from subjects in a Vicon laboratory can be used to generate human motion within the Classic JACK simulation environment. This feature is primarily used in the ergonomic design of equipment that the human must interact with. In this case, the research was evaluating the estimated low-back joint force while rowing in one of three para-rowing setups. This paper describes the method by which Vicon data were recorded, smoothed, imported and applied to the JACK manikin to produce realistic rowing animations. It also describes how the kinetic information from a load cell placed in-line with the ergometer chain was recorded, conditioned and applied to the virtual hands of the JACK manikin to improve the force estimates of the lower back. The low back compressive forces estimated by the Classic JACK program are compared to the NIOSH occupational limits as a point of reference. Findings suggest that males, but not females, rowing in the trunk and arms category were significantly above the NIOSH action limit. Females rowing in the arm and shoulder category were significantly below the NIOSH action limit. Future work will evaluate how design features of the para-rowing setup might be altered to reduce joint loading.

Biomechanical analysis of low back load when sneezing

BackgroundAlthough sneezing is known to induce low back pain, there is no objective data of the load generated when sneezing. Moreover, the approaches often recommended for reducing low back pain, such as leaning with both hands against a wall, are not supported by objective evidence. MethodsParticipants were 12 healthy young men (mean age 23.25±1.54 years) with no history of spinal column pain or low back pain. Measurements were taken using a three-dimensional motion capture system and surface electromyograms in three experimental conditions: normal for sneezing, characterized by forward trunk inclination; stand, in which the body was deliberately maintained in an upright posture when sneezing; and table, in which the participants leaned with both hands on a table when sneezing. We analyzed and compared the intervertebral disk compressive force, low back moment, ground reaction force, trunk inclination angle, and co-contraction of the rectus abdominis and erector spinae muscles in the three conditions. FindingsThe intervertebral disk compressive force and ground reaction force were significantly lower in the stand and table conditions than in the normal condition. The co-contraction index value was significantly higher in the stand condition than in the normal and table conditions. InterpretationWhen sneezing, body posture in the stand or table condition can reduce load on the low back compared with body posture in the normal sneezing condition. Thus, placing both hands on a table or otherwise maintaining an upright body posture appears to be beneficial for reducing low back load when sneezing.

Body segment inertial parameters and low back load in individuals with central adiposity

There is a paucity of information regarding the impact of central adiposity on the inertial characteristics of body segments. Deriving low back loads during lifting requires accurate estimate of inertial parameters. The purpose was to determine the body segment inertial parameters of people with central adiposity using a photogrammetric technique, and then to evaluate the impact on lumbar spine loading. Five participants with central adiposity (waist:hip ratio>0.9, waist circumference>102cm) were compared to a normal BMI group. A 3D wireframe model of the surface topography was constructed, partitioned into 8 body segments and then body segment inertial parameters were calculated using volumetric integration assuming uniform segment densities for the segments. Central adiposity dependent increases in body segment parameters ranged from 12 to 400%, varying across segments (greatest for trunk) and parameters. The increase in mass distribution to the trunk was accompanied by an anterior and inferior shift of the centre of mass. A proximal shift in centre of mass was detected for the extremities, along with a reduction in mass distribution to the lower extremity. L5/S1 torques (392 vs 263Nm) and compressive forces (5918 vs 3986N) were substantially elevated in comparison to the normal BMI group, as well as in comparison to torques and forces predicted using published BSIP equations. Central adiposity resulted in substantial but non-uniform increases in inertial parameters resulting in task specific increases in torque and compressive loads arising from different inertial and physical components.

Prevalence of occupation-related pain among baristas and an examination of low back and shoulder demand during the preparation of espresso-based beverages

Many baristas complain of low back pain (LBP) and upper extremity discomfort while at work. This study documented the prevalence of LBP and shoulder pain, via questionnaire, among a population of baristas to determine whether cumulative low back loads and shoulder moments are associated with pain reporting. Fifty-nine baristas completed the questionnaire; ten were also video-recorded for biomechanical analysis while making espresso beverages and cumulative and peak low back loads and shoulder moments were calculated. Seventy-three percent of those who completed the questionnaire reported having experienced LBP, and half attributed this pain to their job as a barista. Furthermore, 68% reported having experienced shoulder pain and half also attributed this pain to their job. Those who suffered from LBP had higher peak low back compression and those with shoulder pain had, in general, higher moments about their dominant shoulder.

Physical fitness improvements and occupational low-back loading – an exercise intervention study with firefighters

The impact of exercise on firefighter job performance and cardiorespiratory fitness has been studied extensively, but its effect on musculoskeletal loading remains unknown. The aim of this study was to contrast the physical fitness and low-back loading outcomes of two groups of firefighters who completed different exercise programmes. Before and after 12 weeks of exercise, subjects performed a physical fitness test battery, the Functional Movement Screen™ (FMS) and simulated job tasks during which peak L4/L5 joint compression and reaction shear forces were quantified using a dynamic biomechanical model. Subjects who exercised exhibited statistically significant improvements (p < 0.05) in body composition, cardiorespiratory fitness, muscular strength, power, endurance and flexibility, but FMS scores and occupational low-back loading measures were not consistently affected. Firefighters who are physically fit are better able to perform essential job duties and avoid cardiac events, but short-term improvements in physical fitness may not necessarily translate into reduced low-back injury risk.

Cumulative mechanical low-back load at work is a determinant of low-back pain

ObjectivesReported associations of physical exposures during work (eg, lifting, trunk flexion or rotation) and low-back pain (LBP) are rather inconsistent. Mechanical back loads (eg, moments on the low back) as...

L4–L5 compression and anterior/posterior joint shear forces in cabin attendants during the initial push/pull actions of airplane meal carts

The aim of the present study was to assess the acute low back load of cabin attendants during cart handling and to identify working situations which present the highest strain on the worker. In a setup, 17 cabin attendants (ten females and seven males) pushed, pulled and turned a 20kg standard meal cart (L: 0.5m×W: 0.3m×H: 0.92m) loaded with extra 20kg and 40kg, respectively on two different surfaces (carpet and linoleum) and at three floor inclinations (−2°, 0° and +2°). Two force transducers were mounted as handles. Two-dimensional movement analysis was performed and a 4D WATBAK modelling tool was used to calculate the acute L4–L5 load.No working situations created loads greater than the accepted values for single exertions, however compression and anterior/posterior shear forces during pulling and turning were much higher when compared with pushing. There were significant effects of handling the cart on different floor types, at the varying inclinations and with different cart weights. Additionally, when external forces were reduced, the cabin attendants did not decrease push/pull force proportionally and thus the L4–L5 load did not decrease as much as expected.

Unilateral ankle immobilization alters the kinematics and kinetics of lifting

Theoretical and empirical data support the notion that distal lower extremity joint dysfunction could influence the low-back injury potential of workers, but the impact of unilateral ankle immobilization on low-back loading during lifting has yet to be examined. To examine the influence of unilateral ankle immobilization on the kinematics and kinetics of lifting. With and without their right ankle immobilized, 10 men performed laboratory-simulated occupational lifting tasks. Together with force platform data, three-dimensional kinematics of the lumbar spine, pelvis, and lower extremities were collected, and a dynamic biomechanical model was used to calculate peak compressive and shear loads imposed on the L4/L5 intervertebral joint. In comparison to the unaffected conditions, ankle immobilization generally resulted in less knee (0.001 ≤ p ≤ 0.07) and greater lumbar spine (0.001 ≤ p ≤ 0.35) sagittal motion when lifting. Associated with this compensatory movement strategy were greater L4/L5 anterior/posterior reaction shear forces (0.001 ≤ p ≤ 0.25). However, there were cases when individual compensatory movement strategies differed from the "group" response (i.e., subjects increased their sagittal knee motion on the affected side about 8% of the time); this resulted in increased peak L4/L5 joint compression forces without changing the peak L4/L5 anterior-posterior shear forces. Ankle dysfunction can alter the way in which individuals move and load their low-backs when lifting. The different ways in which individuals compensate for personal movement constraints could alter the potential site and mechanism of occupational low-back injury.

2B4-2 モーションセンサからの作業姿勢の読み取りと腰への振動刺激による作業中の腰部負担警告システム

2B4-2 モーションセンサからの作業姿勢の読み取りと腰への振動刺激による作業中の腰部負担警告システム

FMS™ scores and low-back loading during lifting – Whole-body movement screening as an ergonomic tool?

BackgroundPrevious research suggests that a general whole-body movement screen could be used to identify personal movement attributes that promote potentially injurious low-back loading patterns at work. The purpose of this study was to examine the relationship between Functional Movement Screen™ (FMS) composite scores and the low-back loading response to lifting. MethodsFifteen men who scored greater than 14 on the FMS (high-scorers) and 15 height- and weight-matched low-scorers (FMS < 14) performed sagittally symmetric and asymmetric laboratory-based lifting tasks. A three-dimensional dynamic biomechanical model was used to calculate peak low-back loading levels, and the angle of the lumbar spine was captured at the instant when the peak compressive force was applied. ResultsRegardless of the lifting task performed, there were no differences in peak low-back compression (p ≥ 0.4157), anterior/posterior reaction shear (p ≥ 0.5645), or medial/lateral reaction shear (p ≥ 0.2581) forces between the high- and low-scorers. At the instant when peak compressive forces were applied, differences in the lumbar spine angle between high- and low-scores were not statistically significant about the lateral bend (p ≥ 0.4215), axial twist (p ≥ 0.2734), or flexion/extension (p ≥ 0.1354) axes, but there was a tendency for the lumbar spine to be more deviated in the low-scorers. ConclusionsUsing the previously established injury prediction threshold value of 14, the composite FMS score was not related to the peak low-back loading magnitudes in lifting. Though not statistically significant, the tendency for the lumbar spines of low-scorers to be more deviated when the peak low-back compression force was imposed could be biomechanically meaningful because spinal load tolerance varies with posture. Future attempts to modify or reinterpret FMS scoring are warranted given that several previous studies have revealed links between composite FMS scores and musculoskeletal complaints.

The impact of shear force magnitude on cumulative injury load tolerance: a force weighting approach for low-back shear loads

Vertebral joint fatigue life non-linearly decreases with increasing anterior shear force magnitude. Therefore, equal treatment of independent shear force exposures will underestimate low-back injury potential. This investigation developed mathematical functions for deriving appropriate weighting factors (WFs) to be applied in occupational cumulative shear force estimates. Porcine vertebral joints were repetitively loaded in shear to 20%, 40%, 60% or 80% of their calculated shear failure tolerance for 21,600 cycles or until bone failure was detected. Two WF functions were derived from mathematical relationships between sub-maximal shear force magnitude and sustained cumulative shear force to failure. These functions explained 98.2% and 88.6% of the variance in sustained cumulative shear force. Accelerated injury potential represented by WFs greater than unity was assigned to shear forces above 35.6% and 695 N. These weighting approaches will enhance sensitivity in future evaluations between exposure and lost-time/injury for detecting relationships between cumulative shear loading and low-back injury.

Effect of Mental Processing on Low Back Load While Lifting an Object

Biomechanical study using a 3D motion analysis system conducted in a laboratory setting. To determine the effect of mental processing on low back load during lifting. In addition to ergonomic factors such as frequent lifting, work-related psychosocial factors are significant in the onset of disabling back pain. Although the ergonomic effects on low back load while lifting have been investigated and are widely accepted in the workplace, few studies have investigated the effect of psychosocial factors on low back load while lifting. Thirteen healthy subjects lifted a box from the ground in 4 different lifting tasks in randomized order: (1) squat posture with knees flexed; (2) stoop posture with knees extended; (3) squat posture with mental processing using arithmetic tasks; and (4) stoop posture with mental processing using arithmetic tasks. We used a 3D motion analysis system and 4 force plates to record kinematic and kinetic data. We calculated dynamic triaxial low back joint moments and low back compression force as index parameters of low back load under these experimental conditions. Mental processing significantly increased peak low back compression force and low back extension moment, but not lateral flexion or rotation moment, while lifting in both lifting postures. Also, mental processing increased trunk bending angles in the squat posture. Although a tendency for decreased pelvic forward tilt was observed, mental processing did not significantly decrease forward pelvic tilt in the stoop posture. Mental processing during lifting tasks seems to affect both trunk and pelvis angles in the sagittal plane for squat and stoop postures, resulting in increased low back load. The present findings might help explain the effect of ergonomic demands of lifting tasks as well as psychosocial factors responsible for the onset of disabling back pain. 2.

Inter-rater reliability of a video-analysis method measuring low-back load in a field situation

Valid and reliable low-back load assessment tools that can be used in field situations are needed for epidemiologic studies and for ergonomic practice. The aim of this study was to assess the inter-rater reliability of a low-back load video-analysis method in a field setting.Five raters analyzed 50 work site manual material handling tasks of 14 workers. Peak and mean moments at the level of L5S1, and segment angles were obtained using the video-analysis method. Intra-class correlation coefficients (ICCs) and median standard deviations across raters were calculated.ICCs revealed excellent inter-rater reliability (>0.9) for peak and mean moments, ICCs of segment angles were variable. Median standard deviations showed relatively small inter-rater variance for moments (standard deviation <10 Nm) and segment angle variation ranging from 0° to 20°. The proposed video-analysis method, provides a reliable tool for obtaining low-back loads from occupational field tasks.

Low back loads while walking and carrying: comparing the load carried in one hand or in both hands

This study investigates the consequences of carrying load in one hand versus both hands. Six participants walked carrying buckets containing various weights. The weight was either carried in one hand or distributed evenly between both hands. Electromyography, force plate and body kinematic data were input to a three-dimensional anatomically detailed model of the spine to calculate spine loading. Carrying loads in one hand resulted in more load on the low back than when the load was split between both hands. When carrying 30 kg in one hand, the low back compression exceeded 2800 N; however, splitting the load between hands reduced low back compression to 1570 N (reduction of 44%). Doubling the total load by carrying 30 kg in each hand actually produced lower spine compression than when carrying 30 kg in one hand. Balancing the load between both hands when carrying material has merit and should be considered when designing work. Practitioner Summary: Carrying a load in one hand (30 kg) resulted in more spine load than splitting the same load between both hands (15 kg). When carrying double the load in both hands (30 kg in each hand vs. 30 kg in one hand), spine load decreased, suggesting merit in balancing load when designing work.