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

Shoulder and Lower Back Joint Reaction Forces in Seated Double Poling

Overuse injuries in the shoulders and lower back are hypothesized to be common in cross-country sit-skiing. Athletes with reduced trunk muscle control mainly sit with the knees higher than the hips (KH). To reduce spinal flexion, a position with the knees below the hips (KL) was enabled for these athletes using a frontal trunk support. The aim of the study was to compare the shoulder joint (glenohumeral joint) and L4-L5 joint reactions of the KL and KH sitting positions. Five able-bodied female athletes performed submaximal and maximal exercise tests in the sitting positions KL and KH on a ski ergometer. Measured pole forces and 3-dimensional kinematics served as input for inverse-dynamics simulations to compute the muscle forces and joint reactions in the shoulder and L4-L5 joint. This was the first musculoskeletal simulation study of seated double poling. The results showed that the KH position was favorable for higher performance and decreased values of the shoulder joint reactions for female able-bodied athletes with full trunk control. The KL position was favorable for lower L4-L5 joint reactions and might therefore reduce the risk of lower back injuries. These results indicate that it is hard to optimize both performance and safety in the same sit-ski.

Wearable Monitoring Devices for Biomechanical Risk Assessment at Work: Current Status and Future Challenges-A Systematic Review

Background: In order to reduce the risk of work-related musculoskeletal disorders (WMSDs) several methods have been developed, accepted by the international literature and used in the workplace. The purpose of this systematic review was to describe recent implementations of wearable sensors for quantitative instrumental-based biomechanical risk assessments in prevention of WMSDs. Methods: Articles written until 7 May 2018 were selected from PubMed, Scopus, Google Scholar and Web of Science using specific keywords. Results: Instrumental approaches based on inertial measurement units and sEMG sensors have been used for direct evaluations to classify lifting tasks into low and high risk categories. Wearable sensors have also been used for direct instrumental evaluations in handling of low loads at high frequency activities by using the local myoelectric manifestation of muscle fatigue estimation. In the field of the rating of standard methods, on-body wireless sensors network-based approaches for real-time ergonomic assessment in industrial manufacturing have been proposed. Conclusions: Few studies foresee the use of wearable technologies for biomechanical risk assessment although the requirement to obtain increasingly quantitative evaluations, the recent miniaturization process and the need to follow a constantly evolving manual handling scenario is prompting their use.

Effects of the weight configuration of hand load on trunk musculature during static weight holding

The performance of manual material handling tasks is one major cause of lower back injuries. In the current study, we investigated the influence of the weight configuration of hand loads on trunk muscle activities and the associated spinal stability. Thirteen volunteers each performed static weight-holding tasks using two different 9 kg weight bars (with medial and lateral weight configurations) at two levels of height (low and high) and one fixed horizontal distance (which resulted in constant spinal joint moment across conditions). Results of the current study demonstrated that holding the laterally distributed load significantly reduced activation levels of lumbar and abdominal muscles by 9-13% as compared with holding the medially distributed load. We believe such an effect is due to an elevated rotational moment of inertia when the weight of the load is laterally distributed. These findings suggest that during the design and assessment of manual material handling tasks, such as lifting and carrying, the weight configuration of the hand load should be considered. Practitioner summary: Elevated trunk muscle activities were found when holding a medially distributed load vs. a laterally distributed load (with an equivalent external moment to the spine), indicating a reduced spinal stability due to the reduced rotational moment of inertia. The configuration of the hand load should be considered when evaluating manual material handling tasks.

Rationale, Implementation and Evaluation of Assistive Strategies for an Active Back-Support Exoskeleton

Active exoskeletons are potentially more effective and versatile than passive ones, but designing them poses a number of additional challenges. An important open challenge in the field is associated to the assistive strategy, by which the actuation forces are modulated to the user's needs during the physical activity. This paper addresses this challenge on an active exoskeleton prototype aimed at reducing compressive low-back loads, associated to risk of musculoskeletal injury during manual material handling (i.e., repeatedly lifting objects). An analysis of the biomechanics of the physical task reveals two key factors that determine low-back loads. For each factor, a suitable control strategy for the exoskeleton is implemented. The first strategy is based on user posture and modulates the assistance to support the wearer's own upper body. The second one adapts to the mass of the lifted object and is a practical implementation of electromyographic control. A third strategy is devised as a generalized combination of the first two. With these strategies, the proposed exoskeleton can quickly adjust to different task conditions (which makes it versatile compared to using multiple, task-specific, devices) as well as to individual preference (which promotes user acceptance). Additionally, the presented implementation is potentially applicable to more powerful exoskeletons, capable of generating larger forces. The different strategies are implemented on the exoskeleton and tested on 11 participants in an experiment reproducing the lifting task. The resulting data highlights that the strategies modulate the assistance as intended by design, i.e., they effectively adjust the commanded assistive torque during operation based on user posture and external mass. The experiment also provides evidence of significant reduction in muscular activity at the lumbar spine (around 30%) associated to using the exoskeleton. The reduction is well in line with previous literature and may be associated to lower risk of injury.

Hip Abductor Fatigability and Recovery Are Related to the Development of Low Back Pain During Prolonged Standing

A prolonged standing exposure can identify asymptomatic adults who have a higher risk of developing clinical low back pain later in life. Hip abductor cocontraction differences can predict low back pain development during standing exposures. This study’s purpose was to determine if hip abductor strength, fatigability, and recovery during prolonged standing were related to standing-induced low back pain. Forty young, asymptomatic adults (50% female) performed two 2-hour standing sessions; a fatiguing hip abductor exercise was performed prior to 1 of the 2 standing sessions. Hip abductor strength and surface electromyography of gluteus medius and tensor fascia latae were measured. Self-reported low back pain differentiated low back pain developing (PD) and nonpain developing (NPD) groups. The PD group hip abductors fatigued before the NPD group, with similar perceived effort and force losses. Mean power frequency decreases with fatigue were similar between pain groups for all muscles measured after the fatiguing exercise. Unlike NPDs, PDs did not recover force losses after 120 minutes of standing. Hip abductor fatigability may be related to the development of low back pain in this population.

Cumulative Mass and NIOSH Variable Lifting Index Method for Risk Assessment: Possible Relations

Objective The aim of this study was to explore whether the Variable Lifting Index (VLI) can be corrected for cumulative mass and thus test its efficacy in predicting the risk of low-back pain (LBP). Background A validation study of the VLI method was published in this journal reporting promising results. Although several studies highlighted a positive correlation between cumulative load and LBP, cumulative mass has never been considered in any of the studies investigating the relationship between manual material handling and LBP. Method Both VLI and cumulative mass were calculated for 2,374 exposed subjects using a systematic approach. Due to high variability of cumulative mass values, a stratification within VLI categories was employed. Dummy variables (1-4) were assigned to each class and used as a multiplier factor for the VLI, resulting in a new index (VLI_CMM). Data on LBP were collected by occupational physicians at the study sites. Logistic regression was used to estimate the risk of acute LBP within levels of risk exposure when compared with a control group formed by 1,028 unexposed subjects. Results Data showed greatly variable values of cumulative mass across all VLI classes. The potential effect of cumulative mass on damage emerged as not significant ( p value = .6526). Conclusion When comparing VLI_CMM with raw VLI, the former failed to prove itself as a better predictor of LBP risk. Application To recognize cumulative mass as a modifier, especially for lumbar degenerative spine diseases, authors of future studies should investigate potential association between the VLI and other damage variables.

Changes of lumbar posture and tissue loading during static trunk bending

Static trunk bending is an occupational risk factor for lower back pain (LBP). When assessing relative short duration trunk bending tasks, existing studies mostly assumed unchanged spine biomechanical responses during task performance. The purpose of the current study was to assess the biomechanical changes of lumbar spine during the performance of relatively short duration, sustained trunk bending tasks. Fifteen participants performed 40-s static trunk bending tasks in two different trunk angles (30° or 60°) with two different hand load levels (0 or 6.8 kg). Results of the current study revealed significantly increased lumbar flexion and lumbar passive moment during the 40 s of trunk bending. Significantly reduced lumbar and abdominal muscle activities were also observed in most conditions. These findings suggest that, during the performance of short duration, static trunk bending tasks, a shift of loading from lumbar active tissues to passive tissues occurs naturally. This mechanism is beneficial in reducing the accumulation of lumbar muscle fatigue; however, lumbar passive tissue creep could be introduced due to prolonged or repetitive exposure.

Estimating the L5S1 flexion/extension moment in symmetrical lifting using a simplified ambulatory measurement system

Mechanical loading of the spine has been shown to be an important risk factor for the development of low-back pain. Inertial motion capture (IMC) systems might allow measuring lumbar moments in realistic working conditions, and thus support evaluation of measures to reduce mechanical loading. As the number of sensors limits applicability, the objective of this study was to investigate the effect of the number of sensors on estimates of L5S1 moments. Hand forces, ground reaction forces (GRF) and full-body kinematics were measured using a gold standard (GS) laboratory setup. In the ambulatory setup, hand forces were estimated based on the force plates measured GRF and body kinematics that were measured using (subsets of) an IMC system. Using top-down inverse dynamics, L5S1 flexion/extension moments were calculated. RMSerrors (Nm) were lowest (16.6) with the full set of 17 sensors and increased to 20.5, 22 and 30.6, for 8, 6 and 4 sensors. Absolute errors in peak moments (Nm) ranged from 17.7 to 16.4, 16.9 and 49.3 Nm, for IMC setup's with 17, 8, 6 and 4 sensors, respectively. When horizontal GRF were neglected for 6 sensors, RMSerrors and peak moment errors decreased from 22 to 17.3 and from 16.9 to 13 Nm, respectively. In conclusion, while reasonable moment estimates can be obtained with 6 sensors, omitting the forearm sensors led to unacceptable errors. Furthermore, vertical GRF information is sufficient to estimate L5S1 moments in lifting.

Method for measuring tri-axial lumbar motion angles using wearable sheet stretch sensors

BACKGROUND

Body movements, such as trunk flexion and rotation, are risk factors for low back pain in occupational settings, especially in healthcare workers. Wearable motion capture systems are potentially useful to monitor lower back movement in healthcare workers to help avoid the risk factors. In this study, we propose a novel system using sheet stretch sensors and investigate the system validity for estimating lower back movement.

METHODS

Six volunteers (female:male = 1:1, mean age: 24.8 ± 4.0 years, height 166.7 ± 5.6 cm, weight 56.3 ± 7.6 kg) participated in test protocols that involved executing seven types of movements. The movements were three uniaxial trunk movements (i.e., trunk flexion-extension, trunk side-bending, and trunk rotation) and four multiaxial trunk movements (i.e., flexion + rotation, flexion + side-bending, side-bending + rotation, and moving around the cranial-caudal axis). Each trial lasted for approximately 30 s. Four stretch sensors were attached to each participant's lower back. The lumbar motion angles were estimated using simple linear regression analysis based on the stretch sensor outputs and compared with those obtained by the optical motion capture system.

RESULTS

The estimated lumbar motion angles showed a good correlation with the actual angles, with correlation values of r = 0.68 (SD = 0.35), r = 0.60 (SD = 0.19), and r = 0.72 (SD = 0.18) for the flexion-extension, side bending, and rotation movements, respectively (all P < 0.05). The estimation errors in all three directions were less than 3°.

CONCLUSION

The stretch sensors mounted on the back provided reasonable estimates of the lumbar motion angles. The novel motion capture system provided three directional angles without capture space limits. The wearable system possessed great potential to monitor the lower back movement in healthcare workers and helping prevent low back pain.

Application of advanced biomechanical methods in studying low back pain - recent development in estimation of lower back loads and large-array surface electromyography and findings

Low back pain (LBP) is a major public health problem and the leading disabling musculoskeletal disorder globally. A number of biomechanical methods using kinematic, kinetic and/or neuromuscular approaches have been used to study LBP. In this narrative review, we report recent developments in two biomechanical methods: estimation of lower back loads and large-array surface electromyography (LA-SEMG) and the findings associated with LBP. The ability to estimate lower back loads is very important for the prevention and the management of work-related low back injuries based on the mechanical loading model as one category of LBP classification. The methods used for estimation of lower back loads vary from simple rigid link-segment models to sophisticated, optimization-based finite element models. In general, reviewed reports of differences in mechanical loads experienced in lower back tissues between patients with LBP and asymptomatic individuals are not consistent. Such lack of consistency is primarily due to differences in activities under which lower back mechanical loads were investigated as well as heterogeneity of patient populations. The ability to examine trunk neuromuscular behavior is particularly relevant to the motor control model, another category of LBP classification. LA-SEMG not only is noninvasive but also provides spatial resolution within and across muscle groups. Studies using LA-SEMG showed that healthy individuals exhibit highly organized, symmetric back muscle activity patterns, suggesting an orderly recruitment of muscle fibers. In contrast, back muscle activity patterns in LBP patients are asymmetric or multifocal, suggesting lack of orderly muscle recruitment. LA-SEMG was also shown capable of capturing unique back muscle response to manual therapy. In conclusion, estimation of low back load and LA-SEMG techniques demonstrated promising potentials for understanding LBP and treatment effects. Future studies are warranted to fully establish clinical validity of these two biomechanical methods.

Full-shift and task-specific upper extremity muscle activity among US large-herd dairy parlour workers

US large-herd dairy parlour workers experience a high prevalence of musculoskeletal symptoms in the upper extremity. The purpose of this study was to estimate and compare full-shift and task-specific muscle activity of the upper extremity among parlour workers. Surface electromyography data were recorded continuously throughout a full work shift for each participant (n = 60). For a subset of participants (n = 33), muscular effort was estimated for milking task cycles. Lower muscle activity levels and higher per cent muscular rest was observed among rotary parlour participants as compared to herringbone and parallel parlour participants for anterior deltoid, forearm flexor and forearm extensor muscles. These findings suggest rotary parlours may offer workstation designs or work organisational dynamics which may be more beneficial to the health and performance of the worker, as compared to parallel or herringbone parlours. Practitioner Summary: Study findings suggest milking parlour configurations present different biomechanical demands on workers which may influence worker health and performance. Our findings will enable more informed decisions regarding both engineering (e.g. parlour configuration or milking equipment) and administrative (e.g. work organisation) control strategies for large-herd milking parlours.

The Composite Strain Index (COSI) and Cumulative Strain Index (CUSI): methodologies for quantifying biomechanical stressors for complex tasks and job rotation using the Revised Strain Index

The Composite Strain Index (COSI) quantifies biomechanical stressors for complex tasks consisting of exertions at different force levels and/or with different exertion times. The Cumulative Strain Index (CUSI) further integrates biomechanical stressors from different tasks to quantify exposure for the entire work shift. The paper provides methodologies to compute COSI and CUSI along with examples. Complex task simulation produced 169,214 distinct tasks. Use of average, time-weighted average (TWA) and peak force and COSI classified 66.9, 28.2, 100 and 38.9% of tasks as hazardous, respectively. For job rotation the simulation produced 10,920 distinct jobs. TWA COSI, peak task COSI and CUSI classified 36.5, 78.1 and 66.6% jobs as hazardous, respectively. The results suggest that the TWA approach systematically underestimates the biomechanical stressors and peak approach overestimates biomechanical stressors, both at the task and job level. It is believed that the COSI and CUSI partially address these underestimations and overestimations of biomechanical stressors. Practitioner Summary: COSI quantifies exposure when applied hand force and/or duration of that force changes during a task cycle. CUSI integrates physical exposures from job rotation. These should be valuable tools for designing and analysing tasks and job rotation to determine risk of musculoskeletal injuries.

Mechanical demands on the lower back in patients with non-chronic low back pain during a symmetric lowering and lifting task

There is limited information in the literature related to the lower back loading in patients with LBP, particularly those with non-chronic LBP. Toward addressing such a research gap, a case-control study was conducted to explore the differences in lower back mechanical loads between a group of females (n=19) with non-chronic, non-specific LBP and a group of asymptomatic females (n=19). The differences in lower back mechanical loads were determined when participants completed one symmetric lowering and lifting of a 4.5kg load at their preferred cadence. The axial, shearing, and moment components of task demand at the time of peak moment component as well as measures of peak trunk kinematics were analyzed. Patient vs. asymptomatic group performed the task with smaller peak thoracic rotation and peak lumbar flexion. While no differences in the moment component of task demand on the lower back between the patients and controls were found, the shearing (40-50 age group) and axial components of task demand were, respectively, larger and smaller in patients vs.

CONTROLS

Whether alterations in lower back loads in patients with non-chronic LBP are in response to pain or preceded the pain, the long-term exposure to abnormal lower back mechanics may adversely affect spinal structure and increase the likelihood of further injury or pain. Therefore, the underlying reason(s) as well as the potential consequence(s) of such altered lower back mechanics in patients with non-chronic LBP should to be further investigated.

Lumbar contribution to the trunk forward bending and backward return; age-related differences

Age-related differences in lumbar contribution to the trunk motion in the sagittal plane were investigated. Sixty individuals between 20-70 years old in five gender-balanced age groups performed forward bending and backward return with slow and fast paces. Individuals older than 50 years old, irrespective of the gender or pace, had smaller lumbar contribution than those younger than this age. The lumbar contribution to trunk motion was also smaller in female participants than male participants, and under fast pace than under the slow pace. Age-related differences in lumbar contributions suggest the synergy between the active and passive lower back tissues is different between those above and under 50 years old, differences that are likely to affect the lower back mechanics. Therefore, detailed modelling should be conducted in future to find the age-related differences in the lower back mechanics for tasks involving large trunk motion. Practitioner Summary: Lumbar contribution to the sagittal trunk motion was observed to be smaller in individuals above 50 years old than those below this age. This could be an indication of a likely change in the synergy between the active and passive lower back tissues, which may disturb the lower back mechanics.

3D peak and cumulative low back and shoulder loads and postures during greenhouse pepper harvesting using a video-based approach

BACKGROUND

In agricultural field work many tasks have been cited as high priority risk factors for the development of work-related musculoskeletal disorders (WRMDs). Although video-based biomechanical approaches have been effective in documenting the physical demands and risks associated with various occupational and non-occupational tasks, to date, this method has yet to be used to document jobs such as crop harvesting in a greenhouse environment.

OBJECTIVE

To document and assess the postural characteristics and 3D peak and cumulative low back and shoulder loads associated with greenhouse pepper harvesting using a video-based posture sampling approach.

METHODS

Nine male (28.2 (4.1) years) pepper harvesters from a greenhouse in Southwestern Ontario, Canada were videotaped during a normal shift. 3DMatch was used to document working trunk and shoulder postures, from which 3D peak and cumulative forces and moments were quantified.

RESULTS

On average, workers spent the majority of their time in neutral trunk postures (lateral bend: 99.1%; axial twist: 59.9%; flexion: 89.8%). Consistent results were found for the left and right shoulder, with the arms held in a neutral flexion posture 50% of the time or more. Four participants experienced peak L4/L5 compression forces (between 4116.3 N and 5937.0 N) which exceeded the NIOSH Action Limit (3400 N) during the cart pushing/pulling task, but remained below the threshold during picking. Mean cumulative L4/L5 extension and shoulder flexion moments ranged in magnitude from 18.5 Nm to 28.2 Nm, and between 19.4 Nm and 23.2 Nm, respectively, across all tasks.

CONCLUSIONS

The postural characteristics and biomechanical loads associated with greenhouse pepper harvesting were quantified with a video-based biomechanical approach. Further investigations of the physical risk factors for low back and shoulder musculoskeletal disorders is warranted in pepper harvesting, given the postures and loads documented in this study.

An EMG-assisted modeling approach to assess passive lumbar tissue loading in vivo during trunk bending

Lower back pain (LBP) is a condition with high prevalence and high cost both in the United States and around the world. The magnitude of mechanical loading on spine is strongly associated with the occurrence of LBP. Previously, to assess spinal loading, biologically assisted biomechanical models were developed to estimate trunk muscle contraction forces. Loadings on lumbar passive tissues are estimated using anatomical models. However, despite the substantial individual variability in lumbar ligament geometry and viscoelastic properties, the existing anatomical models do not account for these differences. As such, the accuracy of model prediction is compromised especially when mid to full range of trunk motions are involved. This paper describes a new modeling approach to assess lumbar passive tissue loading with the consideration of individual differences in lumbar passive tissue properties. A data set that has trunk bending data from 13 human participants was analyzed; on average, lumbar passive tissue contributes to ∼89% of the total spinal compression force at fully flexed trunk postures; the estimated spinal tissue loadings were in feasible ranges as reported from previous cadaver studies; the estimated spinal loadings were also mostly in agreement with results from previous in vivo studies.

Assisting Frail Seniors With Toileting in a Home Bathroom: Approaches Used by Home Care Providers

Home care providers experience high occupational injury rates. Improving safety is becoming increasingly urgent as this sector expands to support the aging population. Caregivers identify assisting with toileting as a particularly frequent and difficult activity. This mixed-methods observational study identified and analyzed the toileting subactivities that place care providers at the greatest risk of musculoskeletal injury. Eight personal support workers (home care aides) assisted a frail older adult (actor) in a simulated home bathroom. Overall technique and body postures were analyzed. Exposure to musculoskeletal injury risk factors (low back loads and time in extreme trunk postures) was greatest when removing/replacing clothing and providing posterior perineal care; high loads were also possible during transfers. Exposures can be reduced by lowering the pants only to knee level or squatting to raise them. A bidet seat or attachment can perform perineal cleaning, which accounted for 32% of time in severe trunk flexion.

The effects of bending speed on the lumbo-pelvic kinematics and movement pattern during forward bending in people with and without low back pain

BACKGROUND

Impaired lumbo-pelvic movement in people with low back pain during bending task has been reported previously. However, the regional mobility and the pattern of the lumbo-pelvic movement were found to vary across studies. The inconsistency of the findings may partly be related to variations in the speed at which the task was executed. This study examined the effects of bending speeds on the kinematics and the coordination lumbo-pelvic movement during forward bending, and to compare the performance of individuals with and without low back pain.

METHODS

The angular displacement, velocity and acceleration of the lumbo-pelvic movement during the repeated forward bending executed at five selected speeds were acquired using the three dimensional motion tracking system in seventeen males with low back pain and eighteen males who were asymptomatic. The regional kinematics and the degree of coordination of the lumbo-pelvic movement during bending was compared and analysed between two groups.

RESULTS

Significantly compromised performance in velocity and acceleration of the lumbar spine and hip joint during bending task at various speed levels was shown in back pain group (p < 0.01). Both groups displayed a high degree of coordination of the lumbo-pelvic displacement during forward bending executed across the five levels of speed examined. Significant between-group difference was revealed in the coordination of the lumbo-pelvic velocity and acceleration (p < 0.01). Asymptomatic group moved with a progressively higher degree of lumbo-pelvic coordination for velocity and acceleration while the back pain group adopted a uniform lumbo-pelvic pattern across all the speed levels examined.

CONCLUSIONS

The present findings show that bending speed imposes different levels of demand on the kinematics and pattern of the lumbo-pelvic movement. The ability to regulate the lumbo-pelvic movement pattern during the bending task that executed at various speed levels was shown only in pain-free individuals but not in those with low back pain. Individuals with low back pain moved with a stereotyped strategy at their lumbar spine and hip joints. This specific aberrant lumbo-pelvic movement pattern may have a crucial role in the maintenance of the chronicity in back pain.

Estimation of lumbar spinal loading and trunk muscle forces during asymmetric lifting tasks: application of whole-body musculoskeletal modelling in OpenSim

Large spinal compressive force combined with axial torsional shear force during asymmetric lifting tasks is highly associated with lower back injury (LBI). The aim of this study was to estimate lumbar spinal loading and muscle forces during symmetric lifting (SL) and asymmetric lifting (AL) tasks using a whole-body musculoskeletal modelling approach. Thirteen healthy males lifted loads of 7 and 12 kg under two lifting conditions (SL and AL). Kinematic data and ground reaction force data were collected and then processed by a whole-body musculoskeletal model. The results show AL produced a significantly higher peak lateral shear force as well as greater peak force of psoas major, quadratus lumborum, multifidus, iliocostalis lumborum pars lumborum, longissimus thoracis pars lumborum and external oblique than SL. The greater lateral shear forces combined with higher muscle force and asymmetrical muscle contractions may have the biomechanical mechanism responsible for the increased risk of LBI during AL. Practitioner Summary: Estimating lumbar spinal loading and muscle forces during free-dynamic asymmetric lifting tasks with a whole-body musculoskeletal modelling in OpenSim is the core value of this research. The results show that certain muscle groups are fundamentally responsible for asymmetric movement, thereby producing high lumbar spinal loading and muscle forces, which may increase risks of LBI during asymmetric lifting tasks.

Musculoskeletal disorders as a fatigue failure process: evidence, implications and research needs

Mounting evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in musculoskeletal tissues. Evaluations of MSD risk in epidemiological studies and current MSD risk assessment tools, however, have not yet incorporated important principles of fatigue failure analysis in their appraisals of MSD risk. This article examines the evidence suggesting that fatigue failure may play an important role in the aetiology of MSDs, assesses important implications with respect to MSD risk assessment and discusses research needs that may be required to advance the scientific community's ability to more effectively prevent the development of MSDs. Practitioner Summary: Evidence suggests that musculoskeletal disorders (MSDs) may result from a fatigue failure process. This article proposes a unifying framework that aims to explain why exposure to physical risk factors contributes to the development of work-related MSDs. Implications of that framework are discussed.

A Pilot Project for the Study of Ergonomic Interventions in Manufacturing Environments

A participatory ergonomics approach is being tested in two product-matched manufacturing lines framed as intervention and control groups. The project is intended to evaluate the process and the effectiveness of the participatory ergonomics change program. This paper reports on preliminary baseline data on jobs as well as the research process used. Long project time-lines, absence of researcher control, and ongoing change in the manufacturing site pose methodological challenges. Early implementation of visible changes may help foster worker participation. Preparation for post-change evaluation is now underway.

The Contribution of Biomechanical-Biological Interactions of the Spine to Low Back Pain

OBJECTIVE

The objective of this mini-review is to examine a subset of literature that demonstrates multiple interactions between mechanics and biology within the spine and propose how incorporation of these mechano-biologic interactions can be applied to improve the conceptual understanding of tissue tolerances.

BACKGROUND

Low back pain represents a major musculoskeletal problem in the workplace. Traditional biomechanical assessments have employed tissue tolerances as an approach for reducing workplace injuries; however, development of more universal biologically sensitive tolerances requires incorporation of mechano-biologic interactions.

METHODS

A focused literature review addressing the interactions between mechanical loading and biology in the spine.

RESULTS

Mechanical loads applied to the body are distributed across all spatial scales from the body to the tissues to the cells. These mechanical loads regulate cellular metabolism and over time can lead to tissue strengthening or weakening. Mechanical loading also interacts with the biologic environment (e.g., tissue inflammation, nerve sensitization) to influence the perception of pain, thereby changing the risk of experiencing pain. Biologic tissues also exhibit time-dependent changes in mechanical behaviors that occur throughout the day and with disease, suggesting tissue tolerances are time dependent.

CONCLUSION

Incorporating mechano-biologic interactions into the traditional tissue tolerance paradigm through describing tissue tolerances as a function of multiple factors (e.g., preexisting risk factors, underlying pathology, and time) may lead to the development of tissue tolerances that are more representative of the in vivo situation.

APPLICATION

Efforts must work toward incorporating biological concepts into tissue tolerances in order to improve risk assessment tools.

Quantifying the postural demands of patrol officers: a field study

Police officers are at high risk for developing musculoskeletal injuries. This study aimed to determine differences in physical demands of patrol officers during day shifts and night shifts. Sixteen participants were recruited (10 males, 6 females) for in-vehicle observation over one full day shift and one full night shift. Dynamic pressure distribution when seated in the vehicle was assessed and compared between the first and last parts of each shift. Activity characterization and postural analyses were conducted from video that was recorded continuously for the duration of each shift to determine time spent in each task and corresponding postures. Postural analysis and cumulative joint loads were used to identify higher-risk tasks. Several activities caused the officers to adopt non-neutral postures of the neck, shoulders and back. Future work needs to focus on modifying the interior of the vehicle, as well as decreasing exposure time to activities resulting in non-neutral postures.

Failure of the human lumbar motion-segments resulting from anterior shear fatigue loading

An in-vitro experiment was designed to investigate the mode of failure following shear fatigue loading of lumbar motion-segments. Human male lumbar motion-segments (age 32-42 years, n=6) were immersed in Ringer solution at 37°C and repeatedly loaded, using a modified materials testing machine. Fatigue loading consisted of a sinusoidal shear load from 0 N to 1,500 N (750 N±750 N) applied to the upper vertebra of the motion-segment, at a frequency of 5 Hz. During fatigue experiments, several failure events were observed in the dynamic creep curves. Post-test x-ray, CT and dissection revealed that all specimens had delamination of the intervertebral disc. Anterior shear fatigue predominantly resulted in fracture of the apophyseal processes of the upper vertebrae (n=4). Exposure to the anterior shear fatigue loading caused motion-segment instability and resulted in vertebral slip corresponding to grade I and 'mild' grade II spondylolisthesis, as observed clinically.

Biomechanical Evaluation of a Bed Feature to Assist in Turning and Laterally Repositioning Patients

OBJECTIVE

This study investigated the effects of hospital bed features on the biomechanical stresses experienced by nurses when turning and laterally repositioning patients. Turn Assist, a common feature in ICU beds that helps to rotate patients, and side rail orientation were evaluated.

BACKGROUND

Manual patient handling is a risk factor for musculoskeletal injury, and turning patients is one of the most common patient handling activities. No known studies have evaluated bed attributes such as the Turn Assist feature and side rail orientation that may affect the stresses experienced by the nurse.

METHOD

Nine female nurses laterally repositioned and turned a 63-kg and 123-kg subject on an ICU bed while motion capture, ground reaction forces, and hand force data were recorded. Loading of the spine and shoulder was modeled using 3D Static Strength Prediction Program (3DSSPP).

RESULTS

Spine compression and shear forces did not exceed recommended limits when turning or laterally repositioning. However, the mean pull forces required to manually laterally reposition even the 63-kg subject was 340 Newtons, more than 50% greater than limits established in psychophysical testing. Turn Assist considerably reduced spine loading and pull forces for both turning and laterally repositioning. Lowering side rails reduced spinal compression by 11% when turning patients.

CONCLUSION

Laterally repositioning patients as part of turning may pose an injury risk to caregivers. Turn Assist reduces physical loading on nurses when turning and repositioning patients.

APPLICATION

Caregivers should consider using Turn Assist and other aids such as mechanical lifts or sliding sheets especially when turning patients requires lateral repositioning.

Variable Lifting Index (VLI): A New Method for Evaluating Variable Lifting Tasks

OBJECTIVE

We seek to develop a new approach for analyzing the physical demands of highly variable lifting tasks through an adaptation of the Revised NIOSH (National Institute for Occupational Safety and Health) Lifting Equation (RNLE) into a Variable Lifting Index (VLI).

BACKGROUND

There are many jobs that contain individual lifts that vary from lift to lift due to the task requirements. The NIOSH Lifting Equation is not suitable in its present form to analyze variable lifting tasks.

METHOD

In extending the prior work on the VLI, two procedures are presented to allow users to analyze variable lifting tasks. One approach involves the sampling of lifting tasks performed by a worker over a shift and the calculation of the Frequency Independent Lift Index (FILI) for each sampled lift and the aggregation of the FILI values into six categories. The Composite Lift Index (CLI) equation is used with lifting index (LI) category frequency data to calculate the VLI. The second approach employs a detailed systematic collection of lifting task data from production and/or organizational sources. The data are organized into simplified task parameter categories and further aggregated into six FILI categories, which also use the CLI equation to calculate the VLI.

RESULTS

The two procedures will allow practitioners to systematically employ the VLI method to a variety of work situations where highly variable lifting tasks are performed.

CONCLUSIONS

The scientific basis for the VLI procedure is similar to that for the CLI originally presented by NIOSH; however, the VLI method remains to be validated.

APPLICATION

The VLI method allows an analyst to assess highly variable manual lifting jobs in which the task characteristics vary from lift to lift during a shift.

Effect of degeneration on the six degree of freedom mechanical properties of human lumbar spine segments

While the effects of disc degeneration on compression and rotation motions have been studied, there is no data for shear loading. Clinical research has shown that those with low back pain (a potential consequence of degeneration) experience a 75% greater lateral shear force than those without it. Therefore, the aim was to compare the effect of degeneration on spine segment stiffness and phase angle in each of six degree of freedom (6DOF) loading directions. Fourteen intact functional spinal units (FSU) were dissected from human lumbar spines (mean (SD) age 76.2 (11) years, Thompson grades 3 (N = 5, mild), 4 (N = 6, moderate), 5 (N = 3, severe)). Each FSU was tested in ±6DOFs while subjected to a physiological preload, hydration, and temperature (37°C) conditions in a hexapod robot. A one-way ANOVA between degenerated groups was performed on stiffness and phase angle for each DOF. Significant differences in stiffness were found between mild and moderate degenerative groups in lateral shear (p = 0.001), and axial rotation (p = 0.001), where moderate degeneration had decreased stiffness. For phase angle, significant differences were seen in anterior shear (p = 0.017), and axial rotation (p = 0.026), where phase angle for mild degeneration was less than moderate. Trends of stiffness and phase angle changes between degenerative groups were similar within each DOF. Clinically, the identification of the DOFs that are most affected by degeneration could be used in rehabilitation to improve supplemental stabilization of core muscle groups. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1399-1409, 2016.

The Cumulative Lifting Index (CULI) for the Revised NIOSH Lifting Equation: Quantifying Risk for Workers With Job Rotation

OBJECTIVE

The objectives were to: (a) develop a continuous frequency multiplier (FM) for the Revised NIOSH Lifting Equation (RNLE) as a function of lifting frequency and duration of a lifting task, and (b) describe the Cumulative Lifting Index (CULI), a methodology for estimating physical exposure to workers with job rotation.

BACKGROUND

The existing FM for the RNLE (FME) does not differentiate between task duration >2 hr and <8 hr, which makes quantifying physical exposure to workers with job rotation difficult and presents challenges to job designers.

METHOD

Using the existing FMs for 1, 2, and 8 hr of task durations, we developed a continuous FM (FMP) that extends to 12 hr per day. We simulated 157,500 jobs consisting of two tasks each and, using different combinations of Frequency Independent Lifting Index, lifting frequency and duration of lifting. Biomechanical stresses were estimated using the CULI, time-weighted average (TWA), and peak exposure.

RESULTS

The median difference between FME and FMP was ±1% (range: 0%-15%). Compared to CULI, TWA underestimated risk of low-back pain (LBP) for 18% to 30% of jobs, and peak exposure for an assumed 8-hr work shift overestimated risk of LBP for 20% to 25% of jobs. Peak task exposure showed 90% agreement with CULI but ignored one of two tasks.

CONCLUSION

The CULI partially addressed the underestimation of physical exposure using the TWA approach and overestimation of exposure using the peak-exposure approach.

APPLICATION

The proposed FM and CULI may provide more accurate physical exposure estimates, and therefore estimated risk of LBP, for workers with job rotation.

A model for developing job rotation schedules that eliminate sequential high workloads and minimize between-worker variability in cumulative daily workloads: Application to automotive assembly lines

The aim of study is to suggest a job rotation schedule by developing a mathematical model in order to reduce cumulative workload from the successive use of the same body region. Workload assessment using rapid entire body assessment (REBA) was performed for the model in three automotive assembly lines of chassis, trim, and finishing to identify which body part exposed to relatively high workloads at workstations. The workloads were incorporated to the model to develop a job rotation schedule. The proposed schedules prevent the exposure to high workloads successively on the same body region and minimized between-worker variance in cumulative daily workload. Whereas some of workers were successively assigned to high workload workstation under no job rotation and serial job rotation. This model would help to reduce the potential for work-related musculoskeletal disorders (WMSDs) without additional cost for engineering work, although it may need more computational time and relative complex job rotation sequences.

Risk Factors for Low Back Disorders in Saskatchewan Farmers: Field-based Exposure Assessment to Build a Foundation for Epidemiological Studies

BACKGROUND

Studies of many geographical settings and agricultural commodities show that low back disorders are an important public health issue among farmers, who represent a special rural population. However, few studies have examined the impact of low back disorders on farmers' work or the strategies that they adopt to avoid associated pain and disability.

OBJECTIVE

This study protocol will investigate 3 issues related to low back disorders in Saskatchewan farmers: (1) the vibration, heavy lifting, and awkward postures farmers encounter during their work that might contribute to low back disorders; (2) the impact low back disorders have on farmers in terms of their ability to work; and (3) the types of preventative measures and solutions that farmers implement to reduce the occurrence of low back pain.

METHODS

To answer these questions, researchers will travel to 30 farms to make measurements of vibration, lifting, and posture during the farmers' regular work tasks. Farmers will be interviewed about any pain and/or disability using standardized interview questions. Farmers will also be asked about safety measures they have implemented at their farm, such as modified tools or equipment, to reduce the occurrence of low back disorders or pain.

RESULTS

Data collection is currently underway for this study, with the intention to complete all data collection and analysis by the end of 2018.

CONCLUSIONS

Occupational determinants of health such as vibration, heavy lifting, and awkward postures are important in the development and progression of low back disorders, and the results of this study will allow for cost-effective epidemiological studies of these determinants in the future. In identifying prevention strategies, this study will also facilitate future research evaluating the effectiveness of safety measures.

Influence of foot-stretcher height on rowing technique and performance

Strength, technique, and coordination are crucial to rowing performance, but external interventions such as foot-stretcher set-up can fine-tune technique and optimise power output. For the same resultant force, raising the height of foot-stretchers on a rowing ergometer theoretically alters the orientation of the resultant force vector in favour of the horizontal component. This study modified foot-stretcher heights and examined their instantaneous effect on foot forces and rowing technique. Ten male participants rowed at four foot-stretcher heights on an ergometer that measured handle force, stroke length, and vertical and horizontal foot forces. Rowers were instrumented with motion sensors to measure ankle, knee, hip, and lumbar-pelvic kinematics. Key resultant effects of increased foot-stretcher heights included progressive reductions in horizontal foot force, stroke length, and pelvis range of motion. Raising foot-stretcher height did not increase the horizontal component of foot force as previously speculated. The reduced ability to anteriorly rotate the pelvis at the front of the stroke may be a key obstacle in gaining benefits from raised foot-stretcher heights. This study shows that small changes in athlete set-up can influence ergometer rowing technique, and rowers must individually fine-tune their foot-stretcher height to optimise power transfer through the rowing stroke on an ergometer.

Estimating 3D L5/S1 moments and ground reaction forces during trunk bending using a full-body ambulatory inertial motion capture system

Inertial motion capture (IMC) systems have become increasingly popular for ambulatory movement analysis. However, few studies have attempted to use these measurement techniques to estimate kinetic variables, such as joint moments and ground reaction forces (GRFs). Therefore, we investigated the performance of a full-body ambulatory IMC system in estimating 3D L5/S1 moments and GRFs during symmetric, asymmetric and fast trunk bending, performed by nine male participants. Using an ambulatory IMC system (Xsens/MVN), L5/S1 moments were estimated based on the upper-body segment kinematics using a top-down inverse dynamics analysis, and GRFs were estimated based on full-body segment accelerations. As a reference, a laboratory measurement system was utilized: GRFs were measured with Kistler force plates (FPs), and L5/S1 moments were calculated using a bottom-up inverse dynamics model based on FP data and lower-body kinematics measured with an optical motion capture system (OMC). Correspondence between the OMC+FP and IMC systems was quantified by calculating root-mean-square errors (RMSerrors) of moment/force time series and the interclass correlation (ICC) of the absolute peak moments/forces. Averaged over subjects, L5/S1 moment RMSerrors remained below 10Nm (about 5% of the peak extension moment) and 3D GRF RMSerrors remained below 20N (about 2% of the peak vertical force). ICCs were high for the peak L5/S1 extension moment (0.971) and vertical GRF (0.998). Due to lower amplitudes, smaller ICCs were found for the peak asymmetric L5/S1 moments (0.690-0.781) and horizontal GRFs (0.559-0.948). In conclusion, close correspondence was found between the ambulatory IMC-based and laboratory-based estimates of back load.

Characterizing the combined effects of force, repetition and posture on injury pathways and micro-structural damage in isolated functional spinal units from sub-acute-failure magnitudes of cyclic compressive loading

BACKGROUND

Previous research suggests that when the magnitude of peak compressive force applied during cyclic loading exceeds 30% of a functional spinal unit's estimated ultimate compressive tolerance, fatigue failure of the cartilaginous endplate or vertebra will occur before intervertebral disc herniation.

METHODS

Three levels of peak compressive force, three cycle rates and two dynamic postural conditions were examined using a full-factorial design. Cyclic compressive force was applied using a modified material testing apparatus, in accordance with a biofidelic time-varying waveform with synchronous flexion/extension rotation for 5000 cycles. Annulus fibrosus tissue from 36 "survivor" FSUs was excised for histological analysis.

RESULTS

80% of specimens survived 5000 cycles of cyclic loading. A marked difference of the magnitude of peak compressive force was noted in the Kaplan-Meier survival function of experimental conditions that induced fatigue injury. Overall, in the 40% ultimate compressive tolerance load condition, the probability of survival was less than 67%. The micro-structural damage detected in excised samples of annulus fibrosus tissue consisted of clefts and fissures within the intra-lamellar matrix, as well as delamination within the inter-lamellar matrix.

INTERPRETATION

Consistent with previous research, our findings support a threshold of peak compressive force of 30% ultimate compressive tolerance, where cyclic loading above this level will likely result in fatigue injury in less than 5000 cycles of in vitro mechanical loading. However, findings from our histological analyses demonstrate that considerable micro-structural damage occurred in specimens that "survived" the cyclic loading exposure.

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.

Cumulative loads increase at the knee joint with slow-speed running compared to faster running: a biomechanical study

STUDY DESIGN

Biomechanical cross-sectional study.

OBJECTIVE

To investigate the hypothesis that the cumulative load at the knee during running increases as running speed decreases.

BACKGROUND

The knee joint load per stride decreases as running speed decreases. However, by decreasing running speed, the number of strides per given distance is increased. Running a given distance at a slower speed may increase the cumulative load at the knee joint compared with running the same distance at a higher speed, hence increasing the risk of running-related injuries in the knee.

METHODS

Kinematic and ground reaction force data were collected from 16 recreational runners, during steady-state running with a rearfoot strike pattern at 3 different speeds (mean ± SD): 8.02 ± 0.17 km/h, 11.79 ± 0.21 km/h, and 15.78 ± 0.22 km/h. The cumulative load (cumulative impulse) over a 1000-m distance was calculated at the knee joint on the basis of a standard 3-D inverse-dynamics approach.

RESULTS

Based on a 1000-m running distance, the cumulative load at the knee was significantly higher at a slow running speed than at a high running speed (relative difference, 80%). The mean load per stride at the knee increased significantly across all biomechanical parameters, except impulse, following an increase in running speed.

CONCLUSION

Slow-speed running decreases knee joint loads per stride and increases the cumulative load at the knee joint for a given running distance compared to faster running. The primary reason for the increase in cumulative load at slower speeds is an increase in number of strides needed to cover the same distance.

Structural Behavior of Human Lumbar Intervertebral Disc under Direct Shear

Purpose

The intervertebral disc (IVD) is a complex, flexible joint between adjacent vertebral bodies that provides load transmission while permitting movements of the spinal column. Finite element models can be used to help clarify why and how IVDs fail or degenerate. To do so, it is of importance to validate those models against controllable experiments. Due to missing experimental data, shear properties are not used thus far in validating finite element models. This study aimed to investigate the structural shear properties of human lumbar IVDs in posteroanterior (PA) and laterolateral (LL) loading directions.

Methods

Fourteen lumbar IVDs (median age: 49 years) underwent direct shear in PA and LL loading directions. A custom-build shear device was used in combination with a materials testing machine to load the specimens until failure. Shear stiffness, ultimate shear force and displacement, and work to failure were determined.

Results

Each specimen was tested until complete or partial disruption. Median stiffness in PA direction was 490 N/mm and in LL direction 568 N/mm. Median ultimate shear force in the PA direction was 2,877 N and in the LL direction 3,199 N. Work to failure was 12 Nm in the PA and 9 Nm in the LL direction.

Conclusions

This study was an experiment to subject IVDs to direct shear. The results could help us to understand the structure and function of IVDs with regard to mechanical spinal stability, and they can be used to validate finite element models of the IVD.

The influence of lumbar extensor muscle fatigue on lumbar-pelvic coordination during weightlifting

Lumbar muscle fatigue is a potential risk factor for the development of low back pain. In this study, we investigated the influence of lumbar extensor muscle fatigue on lumbar-pelvic coordination patterns during weightlifting. Each of the 15 male subjects performed five repetitions of weightlifting tasks both before and after a lumbar extensor muscle fatiguing protocol. Lumbar muscle electromyography was collected to assess fatigue. Trunk kinematics was recorded to calculate lumbar-pelvic continuous relative phase (CRP) and CRP variability. Results showed that fatigue significantly reduced the average lumbar-pelvic CRP value (from 0.33 to 0.29 rad) during weightlifting. The average CRP variability reduced from 0.17 to 0.15 rad, yet this change ws statistically not significant. Further analyses also discovered elevated spinal loading during weightlifting after the development of lumbar extensor muscle fatigue. Our results suggest that frequently experienced lumbar extensor muscle fatigue should be avoided in an occupational environment.

PRACTITIONER SUMMARY

Lumbar extensor muscle fatigue generates more in-phase lumbar-pelvic coordination patterns and elevated spinal loading during lifting. Such increase in spinal loading may indicate higher risk of back injury. Our results suggest that frequently experienced lumbar muscle fatigue should be avoided to reduce the risk of LBP.

Examining RULA’s Postural Scoring System With Selected Physiological and Psychophysiological Measures

The Rapid Upper Limb Assessment (RULA) survey is a posture-sampling tool used specifically to examine the level of risk associated with upper limb disorders of individual workers. This paper examines the relationship between RULA's postural scoring system and measures of surface electromyography (EMG), self-reports of discomfort, and job attitude questionnaires. Twenty participants each performed a 30-min typing task on a computer in 3 working postures based on RULA's scoring system. A statistically significant difference was found only in perceived discomfort. The perceived discomfort results demonstrated that RULA was able to identify "high risk" postures. The next question we need to ask is, does perceived discomfort result in tissue damage, or does tissue damage yield discomfort?

Development of Human Posture Simulation Method for Assessing Posture Angles and Spinal Loads

Video-based posture analysis employing a biomechanical model is gaining a growing popularity for ergonomic assessments. A human posture simulation method of estimating multiple body postural angles and spinal loads from a video record was developed to expedite ergonomic assessments. The method was evaluated by a repeated measures study design with three trunk flexion levels, two lift asymmetry levels, three viewing angles and three trial repetitions as experimental factors. The study comprised two phases evaluating the accuracy of simulating self and other people's lifting posture via a proxy of a computer-generated humanoid. The mean values of the accuracy of simulating self and humanoid postures were 12° and 15°, respectively. The repeatability of the method for the same lifting condition was excellent (~2°). The least simulation error was associated with side viewing angle. The estimated back compressive force and moment, calculated by a three dimensional biomechanical model, exhibited a range of 5% underestimation. The posture simulation method enables researchers to simultaneously quantify body posture angles and spinal loading variables with accuracy and precision comparable to on-screen posture matching methods.

Age-related changes in trunk neuromuscular activation patterns during a controlled functional transfer task include amplitude and temporal synergies

While healthy aging is associated with physiological changes that can impair control of trunk motion, few studies examine how spinal muscle responses change with increasing age. This study examined whether older (over 65 years) compared to younger (20-45 years) adults had higher overall amplitude and altered temporal recruitment patterns of trunk musculature when performing a functional transfer task. Surface electromyograms from twelve bilateral trunk muscle (24) sites were analyzed using principal component analysis, extracting amplitude and temporal features (PCs) from electromyographic waveforms. Two PCs explained 96% of the waveform variance. Three factor ANOVA models tested main effects (group, muscle and reach) and interactions for PC scores. Significant (p<.0125) group interactions were found for all PC scores. Post hoc analysis revealed that relative to younger adults, older adults recruited higher agonist and antagonistic activity, demonstrated continuous activation levels in specific muscle sites despite changing external moments, and had altered temporal synergies within abdominal and back musculature. In summary both older and younger adults recruit highly organized activation patterns in response to changing external moments. Differences in temporal trunk musculature recruitment patterns suggest that older adults experience different dynamic spinal stiffness and loading compared to younger adults during a functional lifting task.

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.