Low Back Loading Research Articles

Enhancing understanding: Back muscle strength and individual flexibility impact on the flexion-relaxation phenomenon in the lumbar erector spinae

The flexion-relaxation phenomenon (FRP) refers to the deactivation of back muscles during deep forward trunk bending. This study examined the effects of back muscle strength, individual flexibility, and trunk angle on FRP in the back muscles. Forty male participants were classified into four groups according to toe-touch flexibility and back muscle strength. Lumbar erector spinae (LES) activity and the lumbosacral angle (LSA) were measured at incremental trunk flexion angles (0°–90°, with increments of 15°) to analyze FRP. Results indicated significant effects of back muscle strength, flexibility, and trunk angle on LES activity (all p < 0.001). Flexibility (p < 0.05) and trunk angle (p < 0.001) also influenced LSA. Additionally, an interaction between flexibility and trunk angle impacted LES activation (p < 0.001). Flexibility mainly determined FRP onset, while back muscle strength influenced efforts during moderate trunk flexion (30°–60°). These findings indicate that differences in lower back load among individuals with varying back muscle strengths become apparent even at relatively small trunk flexion angles (approximately 30°). When prolonged static trunk flexion in workplace settings places considerable strain on the lower back, we recommend utilizing toe-touch flexibility and back muscle strength assessments as practical screening tools for identifying early and subtle indicators of the FRP in workers.

Upper-Limb and Low-Back Load Analysis in Workers Performing an Actual Industrial Use-Case with and without a Dual-Arm Collaborative Robot

Upper-Limb and Low-Back Load Analysis in Workers Performing an Actual Industrial Use-Case with and without a Dual-Arm Collaborative Robot

Increased Ability to Perceive Relevant Sensory Information Minimizes Low Back Exposures in Lifting.

We have previously shown evidence that some individuals seem to consistently minimize low back loads when lifting, while others do not. However, it is unknown why. Individual differences in ability to perceive relevant sensory information may explain differences in minimization of low back loads during lifting, consistent with considering load reduction in one's movement objective in an optimal feedback control theory framework. The purpose of this study was to investigate whether individuals' ability to perceive proprioceptive information (both force- and posture-senses) at the low back was associated with peak low back loads when performing generic or occupation-specific lifts. Seventy-two participants were recruited to perform 10 barbell (generic) and backboard (occupation-specific) lifts, while whole-body kinematics and ground reaction forces were collected. Peak low back compression and anteroposterior shear forces normalized to body mass were calculated as dependent variables. Both posture matching ability and force matching ability at the heavier force targets were associated with lower means and variability of peak low-back loads in both lift types, albeit with small effect sizes (R2 ≤ .17). These findings support the utility of an optimal feedback control theory framework to explore factors explaining interindividual differences in low back loads during lifting. Further, this evidence suggests improving proprioceptive ability may be a useful strategy in lift training programs designed for workplace injury prevention.

Determining whether biomechanical variables that describe common ‘safe lifting’ cues are associated with low back loads

Lift technique training programs have been implemented to help reduce injury risk, but the underlying content validity of cues used within these programs is not clear. The objective of this study was to determine whether biomechanical variables, that commonly used lifting cues aim to elicit, are associated with resultant low back extensor moment exposures. A sample of 72 participants were recruited to perform 10 repetitions of a floor-to-waist height barbell lift while whole-body kinematics and ground reaction forces were collected. Kinematic, kinetic, and energetic variables representative of characteristics commonly targeted by lifting cues were calculated as predictor variables, while peak and cumulative low back moments were calculated as dependent measures. Multiple regression revealed that 56.6–59.2% of variance in low back moments was explained by predictor variables. From these regression models, generating motion with the legs (both greater hip and knee work), minimizing the horizontal distance of the body to the load, maintaining a stable body position, and minimizing lift time were associated with lower magnitudes of low back moments. These data support that using cues targeting these identified variables may be more effective at reducing peak low back moment exposures via lift training.

The Influence of Contextual and Theoretical Expertise on Generic and Occupation-Specific Lifting Strategy.

To determine whether (i) low back loads and/or (ii) kinematic coordination patterns differed across theoretical expert, contextual expert and novice groups when completing both generic and occupation-specific lifts. Experience has been proposed as a factor that could reduce biomechanical exposures in lifting, but the literature reports mixed effects. The inconsistent relationship between experience and exposures may be partially attributable to the broad classification of experience and experimental lifting protocols not replicating the environment where experience was gained. Purposive sampling was used to recruit 72 participants including theoretical experts (formal training on lifting mechanics), contextual experts (paramedics), and novices. Participants performed 10 barbell and crate (generic) lifts, as well as backboard and stretcher (occupation-specific) lifts while whole-body kinematics and ground reaction forces were collected. Peak low back compression and anteroposterior shear loads normalized to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. No significant differences in low back loads were observed across expertise groups. However, significant differences were seen in kinematic coordination patterns across expertise groups in occupation-specific lifts, but not in generic lifts. Increasing expertise is unlikely to minimize low back loads in lifting. However, contextual expertise did influence lifting kinematics, but only when performing occupationally specific lifts. Contextual expertise may help lifters adopt lifting kinematics that enhance the tolerance of their musculoskeletal system to withstand applied loads, but does not seem to reduce the applied low back loads relative to noncontextual expert groups.

Benchmarking commercially available soft and rigid passive back exoskeletons for an industrial workplace.

Low-back pain is a common occupational hazard for industrial workers. Several studies show the advantages of using rigid and soft back-support passive exoskeletons and exosuits (exos) to reduce the low-back loading and risk of injury. However, benefits of using these exos have been shown to be task-specific. Therefore, in this study, we developed a benchmarking approach to assess exos for an industrial workplace at Hankamp Gears B.V. We assessed two rigid (Laevo Flex, Paexo back) and two soft (Auxivo Liftsuit 1.0, and Darwing Hakobelude) exos for tasks resembling the workplace. We measured the assistive moment provided by each exo and their respective influence on muscle activity as well as the user's perception of comfort and exertion. Ten participants performed four lifting tasks (Static hold, Asymmetric, Squat, and Stoop), while their electromyography and subjective measures were collected. The two rigid exos provided the largest assistance during the Dynamic tasks. Reductions in erector spinae activity were seen to be task-specific, with larger reductions for the two rigid exos. Overall, Laevo Flex offered a good balance between assistive moments, reductions in muscle activity, as well as user comfort and reductions in perceived exertion. Thus, we recommend benchmarking exos for intended use in the industrial workplace. This will hopefully result in a better adoption of the back-support exoskeletons in the workplace and help reduce low-back pain.

Exposure to inclined trunk postures in surgical staff

In surgical staff, low-back pain (LBP) is prevalent and prolonged trunk inclination is hypothesized to be one of its potential causes. The aim of this study was to evaluate the magnitude and duration of trunk inclination in the sagittal plane of surgical assistants during surgical procedures. The three-dimensional trunk orientation was measured in 91 surgical assistants across four medical facilities during surgical procedures using an inertial measurement unit on the thorax. Per participant, Exposure Variation Analysis was used to evaluate the percentage of the total time of trunk inclination (< -10° (backward inclination); -10–10° (upright posture); 10–20° (light inclination); 20–30° (moderate inclination); >30° (strong inclination)) taking into account posture duration (< 10 s; 10–60 s; 60–300 s; > 300 s). Participants reported their LBP history and perceived low-back load during the procedure via a questionnaire. Participants were in an upright posture for 75% [63–84%] (median [interquartile range]) of the total surgery time (average surgery time: 174 min). Trunk inclination was beyond 20° and 30° for 4.3% [2.1–8.7%] and 1.5% [0.5–3.2%] of the surgery time, respectively. In most of the participants, the duration of trunk inclination beyond 20° or 30° was less than 60 s. Questionnaire response rate was 81%. Persistent or repeated LBP was reported by 49% of respondents, and was unrelated to the exposure to inclined trunk postures. It is concluded that other factors than prolonged trunk inclination, for instance handling of loads or prolonged standing may be causally related to the reported LBP in the investigated population.

The influence of transfer distance and pace of work on foot positioning strategies and low back loading in a manual material handling task

Foot positioning strategies are a key parameter in manual materials handling. The objective of this study was to assess the effects of transfer distance, pace and foot positioning on low back loading. Sixteen handlers performed a free handling task with conditions of pace (self-selected and 25% faster), distance (1.5 m, 1.0 m and 0.5 m), height (near-ground and above-waist levels), and mass (10 kg and 20 kg). A linear mixed model was used to evaluate the effects of mass, distance, pace and height on foot positioning occurrences. A non-parametric test (nparLD) was used to evaluate the effects of Pace × Foot positioning and Distance × Foot positioning on L5/S1 sagittal and asymmetrical moments. Positioning the feet aside from the lifting pallet was more prevalent when transferring at shorter transfer distances, high lifting height, and faster pace. When the feet were oriented aside the lifting area, asymmetrical peak moments were slightly higher when transferring at short distance. Facing the lifting pallet may ensure load symmetry, but orienting the feet aside may help to adapt to fast pace or short transfer distance.

The effect of back muscle fatigue on EMG and kinematics based estimation of low-back loads and active moments during manual lifting tasks

This study investigated the effects of back muscle fatigue on the estimation of low-back loads and active low-back moments during lifting, using an EMG and kinematics based model calibrated with data from an unfatigued state. Fourteen participants performed lifting tasks in unfatigued and fatigued states. Fatigue was induced through semi-static forward bending. EMG, kinematics, and ground reaction forces were measured, and low-back loads were estimated using inverse dynamics and EMG-driven muscle model. A regression model was developed using data from a set of calibration lifts, and its accuracy was evaluated for unfatigued and fatigued lifts. During the fatigue-inducing task, the EMG amplitude increased by 2.8 %MVC, representing a 38% increase relative to the initial value. However, during the fatigued lifts, the peak EMG amplitude was found to be 1.6 %MVC higher than that observed during the unfatigued lifts, representing a mere 4% increase relative to the baseline unfatigued peak EMG amplitude. Kinematics and low-back load estimates remained unaffected. Regression model estimation errors remained unaffected for 5 kg lifts, but increased by no more than 5% of the peak active low-back moment for 15 kg lifts. We conclude that the regression-based estimation quality of active low-back moments can be maintained during periods of muscle fatigue, although errors may slightly increase for heavier loads.

Exploring the Addition of Torso Flexion to the LIFFT Analysis Tool

The Lifting Fatigue Failure Tool (LiFFT) is an ergonomic assessment tool based on fatigue failure theory that uses the lower back load moment to evaluate the risk associated with multi-task jobs involving manual lifting. The current LiFFT tool does not account for the moment associated with flexing the lifter's torso. This study explores the incorporation of torso flexion into the LiFFT model while maintaining the relative simplicity of the original LiFFT tool. Automotive manufacturing workers (n=607) performing various tasks were included in the study. Non-manual material handling (MMH) tasks with no MMH load moment were considered "zero" risk. The moment associated with trunk flexion was considered if a worker flexed at the torso during non-MMH assembly tasks. The torso moment from bending was computed using the "average" worker height and weight for the data set used in this study. The proposed model yielded higher odds ratios than the original model.

The influence of bed height as a percentage of participant height on low back forces when boosting a patient up in bed.

Repositioning patients is a frequent task for healthcare workers causing substantial stress to the low back. Patient handling methodologies that reduce low back load should be used. Some studies have observed the effect of bed height on back forces using a limited range of heights. This study details a wider range. The aim of this study was to discover an optimal bed height for reducing low back force when boosting a patient. 11 university students and local residents participated by completing a series of boosts with a 91.6 kg research assistant acting as dependent. The bed was adjusted 3% of participant height and 3 boosts were completed at each height which resulted in 8-10 different bed heights depending on the height of the participant. Motion and force data were collected to estimate low back forces via 3DSSPP. Pearson's R was performed to observe the correlation between caregiver height and low back forces. There were significant negative correlations between bed height and low back compression force at L4-L5 (r = -0.676, p = <0.001) and L5-S1 (r = -0.704, p = <0.001). There were no significant correlations with any shear forces. The highest bed height led to decreased low back compression forces regardless of participant height, but there was not a significant difference in shear forces. Thus, healthcare workers may experience less low back stress with the bed at a higher height. There may be a force tradeoff between the low back and other parts of the body that needs further exploration. Healthcare workers need to be made aware of the implications of adjusting the environment when performing patient handling tasks.

Initiation and accumulation of loading induced changes to native collagen content and microstructural damage in the cartilaginous endplate

BACKGROUND CONTEXTInjury to the cartilaginous endplate (CEP) is linked to clinically relevant low back disorders, including intervertebral disc degeneration and pain reporting. Despite this link to clinical disorders, the CEP injury pathways and the modulating effect of mechanical loading parameters on the pace of damage accumulation remains poorly understood. PURPOSEThis study examined the effect of cyclic loading on the initiation and accumulation of changes to native collagen content (type I, type II) and microstructural damage in the central region of cadaveric porcine CEPs. STUDY DESIGNIn vitro longitudinal study. METHODSOne hundred fourteen porcine cervical spinal units were included (N=6 per group). The study contained a control group (no cyclic loading) and 18 experimental groups that differed by loading duration (1,000, 3,000, 5,000 cycles), joint posture (flexed, neutral), and cyclic peak compression variation (10%, 20%, 40%). Multicolor immunofluorescence staining was used to quantify loading induced changes to type I (ie, subchondral bone) and type II (ie, endplate) native collagen content (fluorescence area, fluorescence intensity) and microstructural damage (pore area [transverse plane], void area along the CEP-bone border [sagittal plane]). RESULTSSignificant main effects of loading duration and posture were observed for fluorescence area and fluorescence intensity of type I and II collagen. In the transverse plane, type II fluorescence area significantly decreased following 1,000 cycles (-12%), but a significant change in fluorescence intensity was not observed until 3,000 cycles (-17%). Type II fluorescence area (-14%) and intensity (-10%) were both significantly less in flexed postures compared to neutral. Similar trends were observed for type I collagen in the sagittal plane sections. Generally, significant changes to fluorescence area were accompanied by the development of microstructural voids along the endplate-subchondral bone border. CONCLUSIONSThese findings demonstrate that microstructural damage beneath the endplate surface occurs before significant changes to the density of native type I and II collagen fibers. Although flexed postures were associated with greater and accelerated changes to native collagen content, the injury initiation mechanism appears similar to neutral. CLINICAL SIGNIFICANCENeutral joint postures can delay the initiation and pace of microdamage accumulation in the CEP during low-to-moderate demand lifting tasks. Furthermore, the management of peak compression exposures appeared relevant only when a neutral posture was maintained. Therefore, clinical low back injury prevention and load management efforts should consider low back posture in parallel with applied joint forces.

들기 작업의 허리부하 평가 및 자세 추천을 위한 작업자 중심의 웹기반 전문가시스템

들기 작업의 허리부하 평가 및 자세 추천을 위한 작업자 중심의 웹기반 전문가시스템

Effect of Trunk Solution® on hemodynamics in the supplementary motor area during walking.

[Purpose] Humans keep their trunks vertical while walking. This defining characteristic is known as upright bipedalism. Research on the neural control of locomotion indicates that not only subcortical structures, but also the cerebral cortex, especially the supplementary motor area (SMA), is involved in locomotion. A previous study suggested that SMA may contribute to truncal upright posture-control during walking. Trunk Solution® (TS) is a trunk orthosis designed to support the trunk in decreasing the low back load. We hypothesized that the trunk orthosis might reduce the burden of truncal control on the SMA. The objective of this study was, therefore, to determine the effect of trunk orthosis on the SMA during walking. [Participants and Methods] Thirteen healthy participants were enrolled in the study. We measured the hemodynamics of the SMA during walking with functional near-infrared spectroscopy (fNIRS). The participants performed two gait tasks on a treadmill: (A) independent gait (usual gait) and (B) supported gait while wearing the TS. [Results] During (A) independent gait, the hemodynamics of the SMA exhibited no significant changes. During (B) gait with truncal support, the SMA hemodynamics decreased significantly. [Conclusion] TS may reduce the burden of truncal control on the SMA during walking.

Development and evaluation of a new assistive device for low back load reduction in caregivers: an experimental study

Low back pain among healthcare professionals is associated with the manual handling of patients. Some bed features for turning and repositioning have been developed; however, the load during patient care remains heavy. We developed a device to reduce low back load in caregivers during patient bedside care and evaluated it objectively and subjectively from a caregiver’s perspective using a randomised crossover study. Overall, 28 clinical nurses and care workers were randomly assigned to two interventional groups: administering care with (Device method) and without (Manual method) the device in an experimental room. We measured the caregiver’s trunk flexion angle using inertial measurement units and video recording during care and then defined a trunk flexion angle of > 45° as the threshold; the variables were analysed using linear mixed models. Subsequently, participants responded to a survey regarding the usability of the device. Trunk flexion time and percentage of time were 26.5 s (95% confidence interval: 14.1 s, 38.9 s) (p < 0.001) and 23.0% (95% confidence interval: 16.4%, 29.6%) (p < 0.001) lower, respectively, in the Device group than in the Manual group. Furthermore, caregivers evaluated the care they could administer with the device as being better than that associated with manual care.

Biomechanical differences in experts' and novices' footstep patterns during a palletizing task

Very few studies have examined differences between experts' and novices' foot positioning and movements during manual materials handling tasks. The impact of footstep patterns on low back loading needs to be better understood. The goals of this study were to characterize foot placement and movements in novices and experts and to assess their impact on back loading considering the height of grasp. The task consisted in transferring 24 15 kg boxes from a pallet to another. Foot placement and movements were classified with a recently developed taxonomy. Results show that experts' feet remained static more often than novices' feet during the lifting phase. Positioning the feet towards the deposit site during lifting increased asymmetrical moments, especially for novices. Positioning one foot forward increased asymmetrical moments for novices. Overall, footstep strategies are an effective indicator of low back exposure and should be considered in ergonomic studies.

Evaluation of an Ergonomic Intervention Demonstrates Reduced Low Back Loads Associated With Commercial Dungeness Crab Harvesting

Evaluation of an Ergonomic Intervention Demonstrates Reduced Low Back Loads Associated With Commercial Dungeness Crab Harvesting

Towards Real-Time Minimum-Input Prediction of Lumbar Moment Based on Flexible Sensors and Machine Learning

Knowledge of low-back loading is essential for understanding and mitigating the risk of low-back overexertion injuries. Conventional data acquisition methods for estimating joint loading are limited to laboratory settings, whereas wearable sensors can provide a mobile and cost-effective alternative. This study investigated the feasibility of learning prediction of L5S1 flexion moment based on kinematics and electromyography (EMG) measurements from flexible sensors. Four machine learning methods were compared, and different subsets of sensor inputs were explored. Results indicated that the support vector machine (SVM) method outperformed others, and a subset of four out of seven sensor locations, namely sacrum, thigh, shank, and thoracic erector spinae, yielded the best predictive accuracy. The study demonstrates that machine learning can unlock the potential of mobile miniaturized flexible sensors in field biomechanics or ergonomics studies.

Healthcare worker choice and low back force between self-chosen and highest bed height when boosting a patient up in bed

Healthcare workers have a high rate of low back injury due to patient handling tasks. These workers receive training in patient handling methods such as adjusting bed height, but often ignore them. In this study, 35 healthcare workers completed patient boosts at a self-chosen bed height and again with the bed in a higher standardised position. Motion capture and force data were collected for analysis. Given the choice, less than half of participants adjusted the bed at all and none of them moved the bed to the highest position (99.1 cm). The self-chosen bed position yielded significantly higher low back force than the higher position at L4-L5 and L5-S1 (p = 0.02, p = 0.01 respectively). Low back forces can be reduced by raising the bed prior to engaging in patient handling tasks, which is a simple step that can reduce forces placed on healthcare workers’ low backs. Practitioner summary: Healthcare workers experience high rates of low back pain secondary to patient handling tasks. In this cross-sectional crossover study, healthcare workers consistently chose a low bed height when boosting a patient, which resulted in higher low back loads compared to the highest bed height.

Comparison of Hip and Low Back Loads between Normal Gait, Axillary Crutch Ambulation and Walking with a Hands-free Crutch in a Healthy Population.

BackgroundInstead of using axillary crutches, using a hands-free crutch (HFC) has been associated with higher functional outcome scores. However, hip and back pain have been reported as side effects.Purpose/HypothesisThe purpose of this study was to compare range of motion and joint reaction forces at the hip and low back between HFC walking, normal walking, and standard crutch walking. It was hypothesized that hip joint reaction forces and low back joint reaction forces would be higher with HFC walking compared with normal walking and axillary crutch walking.Study DesignControlled Laboratory StudyMethodsUsing 3D motion analysis and force plates, kinematics and ground reaction forces were measured in 12 healthy subjects during gait, crutch ambulation and HFC walking. Gait speed, hip and trunk range of motion, and hip and low back reaction forces, were compared using repeated-measures ANOVA.ResultsGait speed during HFC ambulation was reduced 33% compared to crutch ambulation (P<0.001) and 44% compared to normal gait (p<0.001). Hip range of motion was reduced during both crutch conditions compared to gait (p<0.001). Trunk range of motion was greatest during HFC walking compared to both gait and crutch ambulation (p<0.001). Peak hip joint reaction force during HFC walking was 11% lower than during gait (p=0.026) and 30% lower than during crutch walking (p<0.001). Peak low back reaction force during HFC walking was 18% higher than during gait (p=0.032) but not different than during crutch walking.ConclusionHip joint reaction forces during HFC walking did not exceed those during gait or axillary crutch ambulation. However, a reduction in hip motion using the HFC was associated with increases in trunk motion and low-back loading. These could be a cause for reports of low-back pain accompanying HFC usage.Level of EvidenceLevel 3