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The purpose of the current study was to assess the changes in lumbar tissue load sharing mechanism and lumbar range of motion at different trunk flexion postures. Eight participants performed the tasks of changing lumbar posture from extended to flexed posture while maintaining fixed trunk postures (30°, 60°, or 90°). Results of the present study showed that FRP onset was observed in almost all the trials at two conditions of trunk posture (i.e. 60° and 90°). The results also showed that lumbar range of motion changed significantly between the different levels of trunk posture. Findings of the current study could help for better understanding of the dynamics of lumbar active and passive tissue loading during static trunk flexion.

Lumbopelvic coordination describes the relative contributions of lumbar and pelvis to the total trunk flexion/extension motion, which has been identified as a major influential factor to spinal loading. The current study investigated the differences in lumbopelvic coordination between trunk flexion and extension. Thirteen subjects performed pace-controlled trunk flexion/extension motions in the sagittal plane while lumbopelvic continuous relative phase and phase variability were quantified. The results demonstrated that compared with trunk extension, lumbopelvic continuous relative phase and phase variability were 28% and 117% greater in trunk flexion motion, respectively, which indicated a more anti-phase and unstable coordination pattern. Quantifying these coordination patterns helps identifying abnormal patterns and serves as normative benchmarks during low back pain rehabilitation.

Home care tasks, such as patient lifting and transferring, involve forceful exertions and awkward postures and may increase the risk of low back injury. Sixteen home care aides completed simulated client transfers between a bed and wheelchair using a manual transfer method and four transfer devices. Findings suggested that high (bed) to low (wheelchair) transfers produced significant lower hand forces than low to high transfers, while the hand forces using the Beasy board and the Tyvek board were less than the manual’s during transfers in both directions. Average trunk flexion speeds were significantly slower while using devices than using the manual method during these transfers. The usability survey suggests that the Beasy board required less exertion and would be preferred for future client visits.

Occupational tasks performed on uneven ground surfaces are common in agriculture and construction industries. The influence of unilaterally elevated ground surface on lumbar muscle flexion relaxation phenomenon (FRP) during trunk flexion and extension motion has been investigated in the current study. Ten subjects performed trunk flexion and extension motion on flat ground and two unilaterally elevated ground conditions while lumbar muscle EMG and trunk kinematics data were recorded. Results of this study demonstrated clear difference in bilateral lumbar muscle FRP under elevated ground conditions. The current finding can be used to better understand uneven ground surfaces as a risk factor for the development of low back pain.

The purpose of this study was to explore the effect of foot posture on trunk biomechanical responses when experiencing sudden external loading. Fifteen subjects were recruited to perform a series of sudden loading tasks using three different foot postures with two levels of weight. Our results showed that sudden external loading generated the smallest impact when subjects adopted “Staggered Stance”. Compared with “Wide Stance”, “Staggered Stance” significantly decreased the increment of trunk flexion angle, increment of L5/S1 joint moment, and peak L5/S1 joint anterior-posterior shear force by 21.5%, 6.5%, and 22.5%, respectively. Compared with “Narrow Stance”, the decreases were 15.1%, 3.2%, and 16.2% respectively. Heavier load weight resulted in larger spinal impact. The interaction effect between foot posture and magnitude of the load was not significant. The findings of this study could be used in reducing the risk of low back pain when dealing with sudden loading.

The purpose of this pilot study was to characterize the direct measure of physical activity levels and the trunk posture (as a proxy for physical load) among a convenience sample of 49 Patient Care Unit workers (nurses and patient care assistants) for a single work shift. We tested the hypotheses that Patient Care Unit (PCU) worker’s increased trunk posture is associated with their direct measure of physical activity levels during one work-shift. To assess the physical activity and physical load component all participants wore an accelerometer and an inclinometer respectively. A correlation analysis was performed to assess the association between parameters of physical activity (minutes in sedentary activity, minutes in lifestyle activity, minutes in light activity and minutes in moderate activity) with parameters of physical load (number of forward trunk bends to 20° per shift, number of forward trunk bends to 45° per shift). Workers were recruited from two hospitals in Boston, Massachusetts. Eleven participants spent 86% of the time at work with a trunk flexion lower than 15°, they were considered at low exposure for back disorders. Seven PCU workers spent 33% of their work time with a trunk flexion higher than 20°, they were considered at high exposure. Twenty-one workers were classified at a medium exposure for back disorders. A high correlation was found between number of forward trunk bending to 20° per shift (spearman’s correlation: 0.56, p

Floor Coverers have a high prevalence of knee related injuries. The objective of this study is to quantify whole body ergonomics exposure for Floor Coverers in the greater Boston area. A total of 6213 observations (about 100 hours) were made on 49 Floor Coverers by 7 trained observers in 8 construction sites. Awkward leg postures were common. “Kneeling/Crawling” was observed 61.2% of the time. Non-neutral trunk postures were observed frequently. “Severe Flexion” was observed 36.6% of the time, “Mild Flexion” 12.9%. “Manual Material Handling” was observed most frequently during “Hardwood Floor” (36.1%). Hand tools were used more frequently (32.6%) than power tools (5.2%). “Severe Trunk Flexion” did not always lead to heavy trunk load with kneeling postures. Leg postures should be considered before trunk postures were converted to trunk loads. Awkward leg postures are a big problem for Floor Coverers. A majority of the tasks happened near or on the ground.

The majority of the current research associated with pushing and pulling has involved evaluation of manual carts and multi-wheeled containers, but one manual material handling technique that has received limited attention is wheelbarrows. The objective of this study is to evaluate the effects of stabilizer braces on the quantifiable measures of postures of the spine and elbow during wheelbarrow pushing tasks, and to assess users' perceptions regarding the usefulness and effectiveness of the braces. Nine male subjects participated in the study. Subjects pushed the wheelbarrow on a concrete sidewalk of varying inclination (level, uphill, downhill). Trials were performed with and without the use of a customized set of stabilizing forearm braces. The use of stabilizing forearm braces had significant effects on average elbow flexion during uphill pushing trials and average sagittal trunk flexion during downhill pushing trials. The findings indicate that the braces improve the ergonomics of wheelbarrow pushing in some situations and further research is indicated to investigate other biomechanical measures.

The current waste container design at most hospitals, including the UC Davis Medical Center, requires an individual to raise the garbage bag up and out of the container, which involves shoulder flexion above the head and flexion at the waist for most individuals. Overuse injuries due to lifting are very common to the muscles of the shoulder and result in high costs for treating injured workers. The aim of this study was to design a new waste container that will limit the amount of shoulder and trunk flexion required to remove the garbage bags from the container. A waste container was developed, which rotates about two pins on each side to 30 and 45 degree angles from the upright position so that the bags can be removed without lifting them over your head. The degree of shoulder and trunk flexion for the new and old waste container was measured using electrogoniometers. The most important result was that the average degree of shoulder abduction decreased by about 9 degrees from the new bin at 30 degrees and 10 degrees to the new bin at 45 degrees. There also was a significant reduction in sagittal flexion between the old bin and the new bin. The reduction in the level of shoulder abduction and sagittal flexion with this new design may reduce the incidence of injury and improve working conditions for custodial staff in hospital environments.

Spinal stability has been characterized in static but not in dynamic movements. The goal of this study was to determine whether movement pace and direction of dynamic trunk flexion influence the control of spinal stability. Twenty healthy subjects performed dynamic lifting movements at 20 and 40 cycles per minute. Lyapunov exponents were calculated from the measured trunk kinematics to estimate stability. Complexity of torso dynamics required at least five embedded dimensions thereby indicating that torso dynamics requires more than the 3-dimensions of movement for sufficient characterization. Dynamic stability is was greater in slow lifting movement than in fast movements. Asymmetric movements demonstrated greater multi-dimensional kinematic divergence than asymmetric movements. This indicates that the sagittal plane of movement may not be a principle dynamic axis of torso movement. Results provide biomechanical insight regarding the role of workplace design and risk of musculoskeletal instability in dynamic lifting tasks.

A concern related to air travel by people with disabilities is the risk of low-back injuries while transferring the traveler to or from the aircraft seat. Potential contributing factors to this risk are the spatial constraints imposed by the aircraft's interior. This study investigated the effects of such constraints on the trunk angles, angular velocities, and load moment arm during a two-person dependent transfer between a wheelchair and an aircraft seat. Trunk kinematics were recorded as 33 pairs of subjects transferred a dummy to and from an aircraft seat under unconstrained and constrained conditions. The constraints primarily affected the front transferor, increasing peak trunk flexion, lateral bending, twisting, and load moment arm. Effects on the rear transferor were small and appeared to have offsetting effects on injury risk. The results suggest that the row spacing on an aircraft contributes to low-back injury risk during dependent transfers of travelers with disabilities.

Pushing and pulling tasks account for 20% of occupational low-back injury claims but few studies have investigated the neuromuscular control of the spine during these tasks. Primary torso muscle groups recruited during pushing tasks include the rectus abdominis and external obliques. However, theoretical analyses suggest that co-contraction of the paraspinal muscles is necessary to stabilize the spine during flexion exertions. A biomechanical model was implemented to estimate co-contraction and spinal load from measured surface EMG and trunk moment data recorded during trunk flexion and extension exertions. Results demonstrate that co-contraction during flexion exertions was approximately twice the value of co-contraction during extension. Co-contraction accounted for up to 47% of the total spinal load during flexion exertions and spinal load attributed to co-contraction was nearly 50% greater during flexion than during extension exertions despite similar levels of trunk moment. Results underscore the need to consider neuromuscular recruitment when evaluating biomechanical risks. Keywords: Spine; Co-contraction; Push; Manual Materials Handling; Biomechanics

The objective of this study was to identify the sources of temporal variation in trunk postures for self-paced cyclic jobs in a forging plant in order to inform job analysis sampling strategies intended to reliably estimate average long-term exposures to these postures. Repeated video recordings were made on three different individuals in each of the three different jobs over a period of fourteen days. Multimedia Video Task Analysis™ was used to evaluate the percent of time individuals spent in mild trunk flexion (i.e., exceeding 20 degrees) for each of the observation periods. Analysis of variance was used to quantify the within and between worker sources of exposure variability within shifts and across days. The within and between worker components of variability in trunk flexion was very different across the occupations. While in one occupation, no exposure to mild trunk flexion was found, the within- and between-worker components of variance were quite different for the other two occupations. This suggests that different sampling strategies may be needed to reliably estimate the average percentage of time individuals spend working in flexed trunk postures even for cyclic production jobs.

The major objective of this study was to evaluate the effects of mild trunk flexion on localized muscle discomfort in a realistic light assembly task. Secondary objectives included evaluating two instruments commonly used to measure muscular discomfort, determining the level of erector spinae muscle activity during mild trunk flexion, and determining how well low back discomfort predicted loss of torso extension muscle strength. Participants performed a light assembly tasks for 20 minutes while in mild trunk flexion for periods of either 30 or 60 seconds, followed by recovery periods, in which participants stood erect, for periods of either 15, 30, 60 or 120 seconds. Duration of recovery period had a statistically significant effect on localized muscle discomfort of the lower back, upper back and shoulders. Duration of trunk flexion and recovery time had an interactive effect on loss of torso extension strength. Differences in performance between the two discomfort ratings scales were found.

The purpose of this study was to investigate the effects of weight and grip design of concrete cellular blocks on the risk of injury to the lower back. To evaluate the proposed new design, five male participants were asked to perform simulated block laying tasks using the old-design (no grip) and the new-design (with grip). In this study, peak trunk moment, cumulative moment across experimental trial, trunk flexion angle and time required to perform the task were used as dependent variables. Results from the experiment demonstrated that weight of the block and grip/handle designs are both statistically significant (p

This study quantified trunk, hip and knee kinematics during realistic lifting to determine the influence of origin height on lifting style. Ten male participants lifted boxes from several origins ranging from the floor to waist height. The three-dimensional motions of the trunk, hip and knee were recorded. Maximum trunk flexion, knee flexion, and hip flexion increased as lift origin decreased (closer to the floor). Back, knee and hip sagittal angles showed significantly increased correlations as the origins became closer to the floor. Subjects appeared to coordinate their hips, back and knees during the lift for origins below knee height. For lifts above knee height, the lifting style resembled more of a stoop lift while lifts originating below knee height were more of a squat lift. As none of the conditions resulted in pure squat or stoop lifting, discretion is needed in applying the results of pure squat or pure stoop lifting studies to the workplace.

In the so-called Dortmund Lumbar Load Study (DOLLY), the load on the lumbar spine was quantitatively monitored for complete shifts in diverse fields, i.e. for the materials handling tasks in construction and metal-processing industries as well as in a meat-processing factory and for dustbin removal. Video recording of 8 shifts was performed, actual posture was described and the action forces applied at the hands were determined for each work situation. Based on the respective data for posture and handforces, lumbar load was calculated applying the 3D biomechanical model The Dortmunder for each working situation, in total between approx. 4 and 22 thousands per shift. Shift-monitored temporal profiles for several load indicators - trunk flexion and torsional moments, compression and shear forces with respect to the lumbosacral joint - describe the load on the lumbar spine. Comprehensive results with regard to posture, handforces and lumbar load are available. Several load indices regarding load level, duration and the cumulative effects were defined and applied for assessing the analysed jobs. In relation to recommended limits for the maximal disc compression, lumbar load is exceeded in numerous situations during a shift, in particular, with regard to persons of higher age. In a “dose model” developed in this study, the cumulative effect of single-task exposures was considered by superproportional weighting of the compressive force with respect to the corresponding duration of a working task, based on the higher injury potential of high loads compared to - although longer effective - low loads.

This study evaluated the differences in biomechanical model performance and predicted spinal loading on L5/S1 for controlled sagittally symmetric lifting exertions, utilizing three different EMG-assisted biomechanical models comprising different torso anatomical inputs. The first model was based on muscle lines-of-action and prediction of cross-sectional areas from an historical biomechanical model. The second model was based upon observations from an MRI study on torso geometry. The third model consisted of a hybrid approach, where geometric inputs from MRI observations were supplemented with lines-of-action observed from cadaver studies, where necessary. To evaluate the models, spinal loading and model performance was evaluated for thirty-five males performing sagittally symmetric lifting tasks starting from 55 deg trunk flexion to upright neutral. All three models resulted in comparable and acceptable model performance. However, differences were observed in predicted spinal loading. The hybrid model resulted in smaller compression force and sagittal plane shear force when compared to the MRI-only model, and smaller sagittal plane shear forces when compared to the historical biomechanical model. These results indicate that the geometric representation of the torso anatomy needs to be considered when evaluating spinal loading predicted from different biomechanical models for comparison to tolerance estimates in attempts to evaluate risk of injury.

Work-related musculoskeletal disorders affect millions of workers and run up enormous costs by affecting both worker well-being and by production loss. Jobs that require static trunk flexion create biomechanical loads on the muscles and soft-tissue of the lower back, and may contribute to disability caused by low back pain. This paper presents the preliminary results from a laboratory study to identify personal and work factors that determine endurance limits for maintaining non-neutral trunk postures. Subjective and objective measures of performance were recorded using a visual analog scale for discomfort, time of distracting discomfort (TDD), total endurance time (TET) in each posture, and surface electromyography. Endurance time dropped significantly between 15 and 30° of flexion. Older subjects outperformed the younger subjects in TET. Perceived discomfort increased monotonically as a function of trunk flexion angle, with younger subjects perceiving greater discomfort than the older population.

Sudden loading has been shown through epidemiological studies to be linked with onset of low back disorders. The objective of this work was to identify response strategies used by individuals when subjected to sudden loading of the torso and determine the biomechanical consequences of the strategies employed. Eighteen subjects experienced “expected” and “unexpected” loadings while holding either an empty box or a pre-loaded a box. Dependent measures were comprised of kinematic and electromyographic data. Based on trunk flexion measurements subgroups were subgroups using stiff and flexible response strategies were identified. Those using the flexible strategy had greater posterior muscle response (agonist) and less antagonistic response from the anterior muscles. This finding suggest that those employing a flexible strategy may ultimately have a greater risk of over-exertion injury during sudden perturbations

The purpose of this study was to examine the variability in lifting technique kinematics within and between 35 female subjects when lifting light, medium and heavy loads. Each female performed five lifts in a free-style from floor to shoulder-height of a box (37times;29times;27 cm) with handles at three weights: 5, 10 and 15 kg. Polhemus Fastrak™, 3D electromagnetic sensors placed on the wrist, T***I, L***I and S***I spinous processes revealed spinal kinematics that showed increasing variability with heavier loads at the T***I sensor, L***I sensor, thoracic flexion angle, lumbar flexion angle and trunk flexion displacements. The velocity profiles provided similar results of variability for the T***I sensor, L***I sensor, S***I sensor, thoracic and lumbar flexion velocities. In addition, differences in technique were examined between loads using knee bend, box to body distance and trunk mean angles.