Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group--shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10 degrees/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity--specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.     

Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group—shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10°/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity—specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.     

Trunk kinematics of one-handed lifting,and the effects of asymmetry and load weight

Abstract

This study investigated trunk kinematic differences between lifts performed using either one hand (unsupported) or two hands. These effects were studied while beginning the lifts from different asymmetric starting positions and while lifting different load weights. Each subject lifted a box from a lower to an upper platform under one- and two-handed lifting conditions. Subjects wore a lumbar spine electrogoniometer, from which relative motion components were calculated in the trunk's three cardinal planes. Results of this study showed that one-handed lifting resulted in significantly higher ranges of motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion characteristics previously found to be associated with low back disorders were all significantly higher for one-handed lifts. The two-handed lift technique, on the other hand, produced overall faster trunk motions in the sagittal plane and equal or larger acceleration and deceleration magnitudes in all planes of motion. Increases in load asymmetry affected trunk kinematics, in that magnitude values for range of motion, velocity and acceleration became much greater with increasingly asymmetric load positions. Increasing the load weight appeared to have less of an effect on trunk kinematics, with increases in position mostly occurring during sagittal and lateral bending. These results suggest that unsupported one-handed lifting loads the spine more than two-handed lifts, due to the added coupling. Applying these results to a previously developed model, one-handed lifting was also found to increase one's risk of suffering a low back disorder.     

The assessment of material handling strategies in dealing with sudden loading: influences of foot placement on trunk biomechanics

Sudden unexpected loading has been identified as a risk factor of work-related low back pain (LBP). This study investigated the effects of different foot placements and load-releasing locations on trunk biomechanics under an unexpected sudden loading event. Fifteen subjects experienced sudden release of a 6.8-kg external load from symmetric or asymmetric directions while maintaining four different foot placements. The results showed that subjects experienced on average 4.1° less trunk flexion, 6.6 Nm less L5/S1 joint moment and 32.0 N less shear force with staggered stance with the right foot forward (the most preferred placement) compared with wide stance (the least preferred placement). Asymmetric load-releasing positions consistently resulted in smaller impacts on trunk biomechanics than symmetric positions. The findings suggest that staggered stance and asymmetric load-holding position can be used as a protective load-handling posture against LBP caused by sudden loading.     

Age-related biomechanical differences during asymmetric lifting

This study investigated age-related biomechanical differences during asymmetric lifting. Eleven younger and twelve older participants were instructed to lift loads of different weights to an asymmetric destination. The trunk kinematics and low back moments were examined. The results showed that older adults adopted safer lifting strategies compared with younger adults. Specifically, the peak trunk sagittal flexion angle was 32% lower and the peak trunk transverse twisting angle was 22% lower in older adults compared with those in younger adults. It was also found that the average low back moment in the deposit phase was 32% higher in older adults than that in younger adults, most probably due to the age-related increased body weight. Based on these findings and the fact of age-related decreased muscle strengths, physical exercise programs were suggested to be more effective than instructions of safe lifting strategies in LBP risk reduction during asymmetric lifting for older adults. For younger adults, safe lifting strategy instructions might be effective to reduce risks of LBP.     

Multi-segment trunk kinematics during a loaded lifting task for elderly and young subjects

The trunk is frequently modelled as one fixed segment ignoring possible multi-segmental contributions during manual handling. This study compared segmental trunk motion in a young and older population during a lifting task. Twelve elderly and 19 young subjects repeatedly lifted a 5 kg box from bench to shelf under two stance conditions. Displacement and angular trunk segment kinematics were recorded with an electromagnetic tracker system and then analysed. The elderly subjects displayed significantly increased pelvic and trunk displacement and significantly reduced pelvic and lower thorax (T10–L1) range of motion in both stance conditions. Upper thorax (C7–T10) motion was at times greater than lumbar motion and opposite to the lower segments and was related to the task while the lower segments contributed to both equilibrium and task requirements. Decreased segmental trunk angular kinematics may contribute to increased displacement kinematics and place the elderly at increased risk of injury and falling. The pelvis, lumbar spine, low thorax (T10–L1), upper thorax (C7–10) contributed uniquely and synchronously to trunk (C7–S2) mechanics during a lifting task. Reduced angular kinematics of the pelvis and low thorax contributed to increased displacement kinematics and hence increased the risk of falling in the elderly compared to the young. Investigations of trunk mechanics should include multi-segment analysis.     

Experienced workers exhibit distinct torso kinematics/kinetics and patterns of task dependency during repetitive lifts and lowers

Individual differences in work methods may be related to the risk of injury during manual material handling tasks, yet existing evidence comparing experienced workers and novices is mixed. This study assessed torso kinematics and kinetics among six experienced workers and six novices during repetitive lifts/lowers under different task configurations (symmetric vs. asymmetric and lift vs. lower). Several important potential confounding effects were controlled. Peak kinematic and kinetic measures were typically higher among experienced workers and suggestive of exposure to higher levels of low back injury risk, though overall exposure levels were moderate. Work methods used by experienced workers were modified between task conditions, whereas novice behaviours were more consistent. Control of torso kinematics/kinetics may thus not be a primary factor in determining experienced worker's work methods, and future investigation is needed to establish if, or under what conditions, these methods are protective and/or should be the basis for interventions including training.

Practitioner Summary: Whether lifting experience reduces low back injury risk is unclear from earlier findings. Results from a controlled experiment suggest that lifting experience may not be associated consistently with reduced physical demands or injury risk. Further investigation is needed to assess the utility of training based on the methods of experienced workers.     

Muscular and centre of pressure response to sudden release of load in symmetric and asymmetric stoop lifting tasks

Sudden changes in load during asymmetric lifting may be associated with a particularly high risk of loss of balance and spinal injury. Centre of pressure (COP) motions and electromyographic responses of trunk and lower limb muscles were studied in 10 normal male volunteers during sudden release of 20, 40, 60 and 80N stoop lifting loads in symmetric and asymmetric postures. Similar overall COP responses and muscular response strategies to sudden release of load were seen in both postures, although the asymmetric posture showed a larger medio-lateral COP displacements and greater co-contraction asymmetries. While sudden release of load in asymmetric stoop lifting does not seem to involve a greater risk of fall than symmetric lifting, the muscular response results in more complex and asymmetric loading of the trunk, indicating greater localised segmental loading and therefore increased risk of tissue injury.     

Physiological and biomechanical responses to a prolonged repetitive asymmetric lifting activity

This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participant's maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder.     

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.     

Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions

The aim of this study was to assess the effect of an elastic lumbar back support on spinal loading and trunk, hip and knee kinematics while allowing subjects to move their feet during lifting exertions. Predicted spinal forces and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerations, and hip and knee angles were evaluated as a function of wearing an elastic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), and from two different asymmetries at the start of the lift (sagittally symmetric and 60°asymmetry). Subjects were allowed to lift using any lifting style they preferred, and were allowed to move their feet during the lifting exertion. Wearing a lumbar back support resulted in no significant differences for any measure of spinal loading as compared with the no-back support condition. However, wearing a lumbar back support resulted in a modest but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7°), as well as reduction in the sagittal trunk extension velocity (47.2 to 40.2°s^-1). Thus, the use of the elastic lumbar back support provided no protective effect regarding spinal loading when individuals were allowed to move their feet during a lifting exertion.     

Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions

The aim of this study was to assess the effect of an elastic lumbar back support on spinal loading and trunk, hip and knee kinematics while allowing subjects to move their feet during lifting exertions. Predicted spinal forces and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerations, and hip and knee angles were evaluated as a function of wearing an elastic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), and from two different asymmetries at the start of the lift (sagittally symmetric and 60 degrees asymmetry). Subjects were allowed to lift using any lifting style they preferred, and were allowed to move their feet during the lifting exertion. Wearing a lumbar back support resulted in no significant differences for any measure of spinal loading as compared with the no-back support condition. However, wearing a lumbar back support resulted in a modest but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7 degrees), as well as reduction in the sagittal trunk extension velocity (47.2 to 40.2 degrees s(-1)). Thus, the use of the elastic lumbar back support provided no protective effect regarding spinal loading when individuals were allowed to move their feet during a lifting exertion.     

Foot positioning instruction, initial vertical load position and lifting technique: effects on low back loading

This study investigated the effects of initial load height and foot placement instruction in four lifting techniques: free, stoop (bending the back), squat (bending the knees) and a modified squat technique (bending the knees and rotating them outward). A 2D dynamic linked segment model was combined with an EMG assisted trunk muscle model to quantify kinematics and low back loading in 10 subjects performing 19 different lifting movements, using 10.5 kg boxes without handles. When lifting from a 0.05 m height with the feet behind the box, squat lifting resulted in 19.9% (SD 8.7%) higher net moments (p < 0.001) and 17.0% (SD 13.2%) higher compression forces (p < 0.01) than stoop lifting. This effect was reduced to 12.8% (SD 10.7%) for moments and a non-significant 7.4% (SD 16.0%) for compression forces when lifting with the feet beside the box and it disappeared when lifting from 0.5 m height. Differences between squat and stoop lifts, as well as the interaction with lifting height, could to a large extent be explained by changes in the horizontal L5/S1 intervertebral joint position relative to the load, the upper body acceleration, and lumbar flexion. Rotating the knees outward during squat lifts resulted in moments and compression forces that were smaller than in squat lifting but larger than in stoop lifting. Shear forces were small ( < 300 N) at the L4/L5 joint and substantial (1100 - 1400 N) but unaffected by lifting technique at the L5/S1 joint. The present results show that the effects of lifting technique on low back loading depend on the task context.     

Biomechanical evaluation of nursing tasks in a hospital setting

A field study was conducted to investigate spinal kinematics and loading in the nursing profession using objective and subjective measurements of selected nursing tasks observed in a hospital setting. Spinal loading was estimated using trunk motion dynamics measured by the lumbar motion monitor (LMM) and lower back compressive and shear forces were estimated using the three-dimensional (3D) Static Strength Prediction Program. Subjective measures included the rate of perceived physical effort and the perceived risk of low back pain. A multiple logistic regression model, reported in the literature for predicting low back injury based on defined risk groups, was tested. The study results concluded that the major risk factors for low back injury in nurses were the weight of patients handled, trunk moment, and trunk axial rotation. The activities that required long time exposure to awkward postures were perceived by nurses as a high physical effort. This study also concluded that self-reported perceived exertion could be used as a tool to identify nursing activities with a high risk of low-back injury.     

Disturbance and recovery of trunk mechanical and neuromuscular behaviours following repetitive lifting: influences of flexion angle and lift rate on creep-induced effects

Repetitive lifting is associated with an increased risk of occupational low back disorders, yet potential adverse effects of such exposure on trunk mechanical and neuromuscular behaviours were not well described. Here, 12 participants, gender balanced, completed 40 min of repetitive lifting in all combinations of three flexion angles (33, 66, and 100% of each participant's full flexion angle) and two lift rates (2 and 4 lifts/min). Trunk behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness and reflexive responses were compromised after lifting exposures, with larger decreases in stiffness and reflexive force caused by larger flexion angles, which also delayed reflexive responses.Consistent effects of lift rate were not found. Except for reflex delay no measures returned to pre-exposure values after 20 min of recovery. Simultaneous changes in both trunk stiffness and neuromuscular behaviours may impose an increased risk of trunk instability and low back injury.

Practitioner summary An elevated risk of low back disorders is attributed to repetitive lifting. Here, the effects of flexion angle and lift rate on trunk mechanical and neuromuscular behaviours were investigated. Increasing flexion angle had adverse effects on these outcomes, although lift rate had inconsistent effects and recovery time was more than 20 min.     

A history of low back pain affects pelvis and trunk mechanics during a sustained lift/lower task

This study compared three-dimensional trunk and pelvis range of motion (ROM) during a sustained asymmetric box lift/lower task between a group with a history of low back pain (HBP, n = 9) and a group with no history of low back pain (NBP, n = 9). Participants lifted an 11-kg box for 10 min at 12 cycles/min from ankle height in front to shelves 45 deg off-centre at waist height. Kinematic data were collected at the beginning (min1), middle (min5) and end of the bout (min9). Two-way analyses of variance were performed for all variables. Pelvis and trunk transverse ROM were similar at min1. By min9, HBP group did not change (31.9 ± 9 deg); however, ROM decreased in NBP group (21.6 ± 6 deg, p < 0.05). Therefore, despite no current pain, the HBP group demonstrated protective lifting mechanics compared to controls. Also discussed are implications for studying lifting paradigms at sub-maximal effort over longer periods of time.

Practitioner summary: Differences between groups over time demonstrate residual consequences of low back pain (LBP) in a manual materials handling scenario. Individuals with a history of LBP (pain free for 6 months) demonstrated more conservative lifting mechanics towards the end of the bout compared to controls with no history of LBP.     

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.     

Foot positioning instruction,initial vertical load position and lifting technique: effects on low back loading

This study investigated the effects of initial load height and foot placement instruction in four lifting techniques: free, stoop (bending the back), squat (bending the knees) and a modified squat technique (bending the knees and rotating them outward). A 2D dynamic linked segment model was combined with an EMG assisted trunk muscle model to quantify kinematics and low back loading in 10 subjects performing 19 different lifting movements, using 10.5 kg boxes without handles. When lifting from a 0.05 m height with the feet behind the box, squat lifting resulted in 19.9% (SD 8.7%) higher net moments (p < 0.001) and 17.0% (SD 13.2%) higher compression forces (p < 0.01) than stoop lifting. This effect was reduced to 12.8% (SD 10.7%) for moments and a non-significant 7.4% (SD 16.0%) for compression forces when lifting with the feet beside the box and it disappeared when lifting from 0.5 m height. Differences between squat and stoop lifts, as well as the interaction with lifting height, could to a large extent be explained by changes in the horizontal L5/S1 intervertebral joint position relative to the load, the upper body acceleration, and lumbar flexion. Rotating the knees outward during squat lifts resulted in moments and compression forces that were smaller than in squat lifting but larger than in stoop lifting. Shear forces were small ( < 300 N) at the L4/L5 joint and substantial (1100 – 1400 N) but unaffected by lifting technique at the L5/S1 joint. The present results show that the effects of lifting technique on low back loading depend on the task context.     

Assessment of engineering controls designed for handling unstable loads: An electromyography assessment

Low back injury due to manual lifting is historically prevalent in labor intensive industries. Improving risk management options is necessary to reduce the risk of low back injury. Workers lifting unstable loads are at greater risk of back injury compared to workers lifting stable loads. This study focused on the effect of engineering controls on trunk muscle activity. Engineering controls were designed to control the instability of a liquid load. Thirty-nine healthy subjects manually lifted asymmetrically in the transverse direction stable loads, unstable loads, and unstable loads with engineering controls. Trunk and load kinematic and trunk muscle electromyography data were collected during lifting. Unstable loads with engineering controls significantly (p < 0.001) reduced trunk muscle activity compared to unstable loads. Engineering controls should be implemented to reduce the risk of injury to workers handling unstable liquid loads.Relevance to industryManually handling containers filled with liquids is necessary in many industrial workplaces. Risk management solutions for low back injury due to manual lifting of such loads should focus on reducing muscular demand. This study demonstrates that engineering controls designed to increase the stability of a liquid load reduced muscular demand.     

Effect of lifting height and load mass on low back loading

The objective of this study was to quantify the effect of lifting height and mass lifted on the peak low back load in terms of net moments, compression forces and anterior–posterior shear forces. Ten participants had to lift a box using four handle heights. Low back loading was quantified using a dynamic 3-D linked segment model and a detailed electromyographic driven model of the trunk musculature. The effects of lifting height and lifting mass were quantified using a regression technique (GEE) for correlated data. Results indicate that an increase in lifting height and a decrease in lifting mass were related to a decrease in low back load. It is argued that trunk flexion is a major contributor to low back load. For ergonomic interventions it can be advised to prioritise optimisation of the vertical location of the load to be lifted rather than decreasing the mass of the load for handle heights between 32 cm and 155 cm, and for load masses between 7.5 and 15 kg. Lifting height and load mass are important determinants of low back load during manual materials handling. This paper provides the quantitative effect of lifting height and mass lifted, the results of which can be used by ergonomists at the workplace to evaluate interventions regarding lifting height and load mass.