Back Load Research Articles

Validation of lumbar spine loading from a musculoskeletal model including the lower limbs and lumbar spine

Low back mechanics are important to quantify to study injury, pain and disability. As in vivo forces are difficult to measure directly, modeling approaches are commonly used to estimate these forces. Validation of model estimates is critical to gain confidence in modeling results across populations of interest, such as people with lower-limb amputation. Motion capture, ground reaction force and electromyographic data were collected from ten participants without an amputation (five male/five female) and five participants with a unilateral transtibial amputation (four male/one female) during trunk-pelvis range of motion trials in flexion/extension, lateral bending and axial rotation. A musculoskeletal model with a detailed lumbar spine and the legs including 294 muscles was used to predict L4-L5 loading and muscle activations using static optimization. Model estimates of L4-L5 intervertebral joint loading were compared to measured intradiscal pressures from the literature and muscle activations were compared to electromyographic signals. Model loading estimates were only significantly different from experimental measurements during trunk extension for males without an amputation and for people with an amputation, which may suggest a greater portion of L4-L5 axial load transfer through the facet joints, as facet loads are not captured by intradiscal pressure transducers. Pressure estimates between the model and previous work were not significantly different for flexion, lateral bending or axial rotation. Timing of model-estimated muscle activations compared well with electromyographic activity of the lumbar paraspinals and upper erector spinae. Validated estimates of low back loading can increase the applicability of musculoskeletal models to clinical diagnosis and treatment.

Effect of Tenon Size on Static Front to Back Loading Performance of Wooden Chairs in Comparison with Acceptable Design Loads

The effects of tenon size were investigated relative to the front to back loading performance of Scots pine (Pinus sylvestris L.) chairs. Forty-five chair frames were constructed with mortise and tenon joints with 9 tenon sizes. Joints were assembled with a 65% solids polyvinyl acetate (PVAc) adhesive. The front to back loading performance of chairs was compared to the acceptable design load levels given in the American Library Association (ALA) specifications. Chair frames were structurally analyzed with the Finite Element Method (FEM) to obtain the moment acting on each joint under loading. The results indicated that a chair became stronger as either tenon width or length increased, but was most affected by its length. As a result of structural analyses, front leg to side rail and back leg to side rail joints carried approximately 73% of the total moment that was induced under the front to back loading. According to the comparison results with acceptable design loads, chairs constructed with 40 mm × 50 mm tenons could meet light service (domestic usage), while the chairs constructed with 50 mm × 50 mm tenons could meet medium service. The chairs constructed with other sizes could not meet any acceptable levels, and thus need reinforcement.

Effects of backpack loads and positions on the variability of gait spatiotemporal parameters in young adults

AbstractIntroduction: People carry backpacks of different weight in different positions every day. The effects of backpack wearing under different loads and positions were assessed according to the gait’s spatiotemporal parameters and their variability in young adults. Methods Twenty-one subjects performed trials of 4 min in the conditions: control condition with no backpack; bilateral back load consisting of 10% body weight (BW); bilateral back load of 20% BW (B20); unilateral load of 10% BW; unilateral load with 20% BW (U20); bilateral frontal load with 10% BW; bilateral frontal load with 20% BW. Results Step length (SL) and step frequency (SF) show that frontal conditions differed from others as seen in B20. Gait cycle phases showed an increase in the B20 condition for double stance phase and stance phase, swing phase presented reduction in the B20 condition. There were significant main effects in position for SL, SF, and walk ratio, in load only for stride width. The highest variability of spatiotemporal parameters occurred in the U20 condition. All load conditions with 20% BW showed a greater variability when compared to the 10% BW counterpart. Conclusion We concluded that young adults can cope with up to a 15% BW load under a bilateral back position, but in the frontal position not even a 10% BW load was proven to be a safe limit. 20% BW loads should be avoided in any position. These recommendations may assure increased gait stability, decreased trunk forward lean and decreased muscle activation and fatigue reducing back pain occurrence.

Identifying interactive effects of task demands in lifting on estimates of in vivo low back joint loads

This investigation examined interactions between the magnitude of external load, movement speed and (a)symmetry of load placement on estimates of in vivo joint loading in the lumbar spine during simulated occupational lifting. Thirty-two participants with manual materials handling experience were included in the study. Three-dimensional motion data, ground reaction forces, and activation of six bilateral trunk muscle groups were captured while participants performed lifts with two loads at two movement speeds and using two load locations. L4-L5 joint compression and shear force-time histories were estimated using an EMG-assisted musculoskeletal model of the lumbar spine. Results from this investigation provide strong evidence that known mechanical low back injury risk factors should not be viewed in isolation. Rather, injury prevention efforts need to consider the complex interactions that exist between external task demands and their combined influence on internal joint loading.

Feasibility of a Biomechanically-Assistive Garment to Reduce Low Back Loading During Leaning and Lifting.

The purpose of this study was: 1) to design and fabricate a biomechanically-assistive garment which was sufficiently lightweight and low-profile to be worn underneath, or as, clothing, and then 2) to perform human subject testing to assess the ability of the garment to offload the low back muscles during leaning and lifting. We designed a prototype garment which acts in parallel with the low back extensor muscles to reduce forces borne by the lumbar musculature. We then tested eight healthy subjects while they performed common leaning and lifting tasks with and without the garment. We recorded muscle activity, body kinematics, and assistive forces. The biomechanically-assistive garment offloaded the low back muscles, reducing erector spinae muscle activity by an average of 23-43% during leaning tasks, and 14-16% during lifting tasks. Experimental findings in this study support the feasibility of using biomechanically-assistive garments to reduce low back muscle loading, which may help reduce injury risks or fatigue due to high or repetitive forces. Biomechanically-assistive garments may have broad societal appeal as a lightweight, unobtrusive, and cost-effective means to mitigate low back loading in daily life.

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.

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.

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Development and validation of an easy-to-use risk assessment tool for cumulative low back loading: The Lifting Fatigue Failure Tool (LiFFT)

Recent evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in affected tissues. This paper describes a new low back exposure assessment tool (the Lifting Fatigue Failure Tool [LiFFT]), which estimates a “daily dose” of cumulative loading on the low back using fatigue failure principles. Only three variables are necessary to derive the cumulative load associated with a lifting task: the weight of the load, the maximum horizontal distance from the spine to the load, and the number of repetitions for tasks performed during the workday. The new tool was validated using two existing epidemiological databases: the Lumbar Motion Monitor (LMM) database, and a database from a U.S. automotive manufacturer. The LiFFT cumulative damage metric explained 92% of the deviance in low back disorders (LBDs) in the LMM database and 72–95% of the deviance in low back outcomes in the automotive database (depending on the outcome measure). Thus, LiFFT is practitioner friendly and its cumulative damage metric highly related to low back outcomes.

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.

Lower Back Joint Torque Relief Frame Mechanism for Lifting a Heavy Object by Hand

In this paper, a novel lower back joint torque relief frame mechanism was proposed. Then the function of proposed mechanism was evaluated by calculated value of lower back joint torque. There are many tasks that are required to unnatural postures and difficult hard work that mechanization is difficult in a wide range of fields such as care, logistics and agriculture. In our method, lifting a heavy object load by the subject arm is reduced by using a proposed mechanism which holds the subject's lower back joint at the chest, the lower back and the thigh. In order to consider the function of the mechanism, an experiment of one subject lift 10.0 kg object was conducted. At this time, the forces which occurred at the chest, the lower back and the thigh were measured by load cells. From the experiment, the proposed mechanism was able to reduce the values of lower back joint torque. Further, the values were at least 2 Nm. The proposed mechanism has a function which reduces the load of the lower back by lower back joint torque relief.

Using a marker-less method for estimating L5/S1 moments during symmetrical lifting

The aim of this study is to analyze the validity of a computer vision-based method to estimate 3D L5/S1 joint moment during symmetrical lifting. An important criterion to identify the non-ergonomic lifting task is the value of net moment at L5/S1 joint. This is usually calculated in a laboratory environment which is not practical for on-site biomechanical analysis. The validity of the proposed method, was assessed externally by comparing the results with a lab-based reference method and internally by comparing the estimated L5/S1 joint moments from top-down model and bottom-up model. It was shown that no significant differences in peak and mean moments between the two methods and intra-class correlation coefficients revealed excellent reliability of the proposed method (>0.91). The proposed method provides a reliable tool for assessment of lower back loads during occupational lifting and can be an alternative when the use of marker-based motion tracking systems is not possible.

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

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. 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. 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. 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. 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.

How to quantify the transition phase during golf swing performance: Torsional load affects low back complaints during the transition phase

ABSTRACTThe transition phase of a golf swing is considered to be a decisive instant required for a powerful swing. However, at the same time, the low back torsional loads during this phase can have a considerable effect on golf-related low back pain (LBP). Previous efforts to quantify the transition phase were hampered by problems with accuracy due to methodological limitations. In this study, vector-coding technique (VCT) method was proposed as a comprehensive methodology to quantify the precise transition phase and examine low back torsional load. Towards this end, transition phases were assessed using three different methods (VCT, lead hand speed and X-factor stretch) and compared; then, low back torsional load during the transition phase was examined. As a result, the importance of accurate transition phase quantification has been documented. The largest torsional loads were observed in healthy professional golfers (10.23 ± 1.69 N · kg−1), followed by professional golfers with a history of LBP (7.93 ± 1.79 N · kg−1), healthy amateur golfers (1.79 ± 1.05 N · kg−1) and amateur golfers with a history of LBP (0.99 ± 0.87 N · kg−1), which order was equal to that of the transition phase magnitudes of each group. These results indicate the relationship between the transition phase and LBP history and the dependency of the torsional load magnitude on the transition phase.

Efficacy of a trunk orthosis with joints providing resistive force on low back load during level walking in elderly persons.

PurposeThe effects of lumbosacral and spinal orthoses on low back pain and gait are not exactly clear. We previously developed a trunk orthosis with joints providing resistive force on low back load to decrease such load, and confirmed its positive effects during level walking in healthy young adults. Therefore, we aimed to determine the efficacy of this trunk orthosis during level walking in healthy elderly subjects.MethodsFifteen community-dwelling elderly subjects performed level walking at a self-selected speed without an orthosis, with our orthosis, and with a lumbosacral orthosis. Kinematic and kinetic data were recorded using a three-dimensional motion analysis system, and erector spinae activity was recorded by electromyography.ResultsWhen comparing the three conditions, our orthosis showed the following effects: it decreased the peak extension moment, increased the peak flexion moment, decreased the lateral bending angle, increased the peak thoracic extension angle, and had significantly lower erector spinae activity and significantly larger peak pelvic forward tilt angles.ConclusionOur orthosis with joints providing resistive force decreased low back load and modified trunk and pelvis alignments during level walking in healthy elderly people.

Prolonged Intermittent Trunk Flexion Increases Trunk Muscles Reflex Gains and Trunk Stiffness.

The goal of the present study was to determine the effects of prolonged, intermittent flexion on trunk neuromuscular control. Furthermore, the potential beneficial effects of passive upper body support during flexion were investigated. Twenty one healthy young volunteers participated during two separate visits in which they performed 1 hour of intermittent 60 seconds flexion and 30 seconds rest cycles. Flexion was set at 80% lumbar flexion and was performed with or without upper body support. Before and after intermittent flexion exposure, lumbar range of motion was measured using inertial measurement units and trunk stability was assessed during perturbations applied in the forward direction with a force controlled actuator. Closed-loop system identification was used to determine the trunk translational admittance and reflexes as frequency response functions. The admittance describes the actuator displacement as a function of contact force and to assess reflexes muscle activation was related to actuator displacement. Trunk admittance gain decreased after unsupported flexion, while reflex gain and lumbar range of motion increased after both conditions. Significant interaction effects confirmed a larger increase in lumbar range of motion and reflex gains at most frequencies analysed following unsupported flexion in comparison to supported flexion, probably compensating for decreased passive tissue stiffness. In contrast with some previous studies we found that prolonged intermittent flexion decreased trunk admittance, which implies an increase of the lumped intrinsic and reflexive stiffness. This would compensate for decreased stiffness at the cost of an increase in cumulative low back load. Taking into account the differences between conditions it would be preferable to offer upper body support during activities that require prolonged trunk flexion.

New and Improved: Our Experience with the 22G Cook Fiducial Needle System

Traditionally fiducial markers have served as reference points and have been placed by Endoscopic ultrasound (EUS), intraoperatively, or percutaneously via ultrasound or CT. EUS guided placement has increased in popularity recently due to the ability of EUS to allow for close proximity to deeper abdominal structures not easily accessible via surgical or percutaneous routes. One limitation to the growth of this technique has been the need to individually back load and seal the fiducial using bone wax or recently described wet fill technique. The back loading procedure increases the time for the procedure, may increase risk to the operator if one is loading fiducials into dirty needles (when more than one fiducial is required), or increase cost if new FNA needles are used for each fiducial. The new 22G Cook Fiducial needle is preloaded with four gold fiducials, which solves many of the problems mentioned. Four patients underwent fiducial placement with the 22G Cook Fiducial Needle System. A 63 year old male with metastatic renal cell carcinoma to the stomach and proximal duodenum presented with melena. EGD showed a large ulcerated bleeding mass in the anterior wall of the stomach. Fiducials were placed to allow for selective embolization. A 52 year old male presented with progressive dysphagia and weight loss. EGD revealed a large partially obstructing lower esophageal mass. Pathology confirmed esophageal adenocarcinoma and he underwent fiducial placement to assist in intensity modulated neoadjuvant radiation therapy. A 68 year old male with rectal adenocarcinoma had a 10 mm mass in the left lobe of the liver. The patient was to undergo neo-adjuvant therapy followed by surgical resection of the primary tumor and wedge resection of the solitary liver lesion. Fiducial placement was requested prior to neoadjuvant therapy to mark the position of the mass for localization during the eventual wedge resection. A 57 year old male with abdominal pain had an EUS which showed an ill-defined mass in the pancreatic neck with background chronic pancreatitis. EUS FNA of the mass was positive for adenocarcinoma. Due to ill-defined nature of the mass, the presence of background chronic pancreatitis and for accurate surgical localization fiducial placement was requested. We have shown that this needle is easy and quick to use in a variety of settings with subsequent excellent visualization of the fiducial with no immediate or delayed complications.

Static Front to Back Loading Capacity of Wood Chairs and Relationship between Chair Strength and Individual Joint Strength

The relationship between the static front to back loading capacity of chairs and the moment capacities of the joints used in their side frames was investigated. The secondary purpose of the study was to determine the effect of tenon sizes on front to back loading capacity of chairs. The moment capacities of round edge mortise and tenon L-shaped and T-shaped joints constructed of Turkish beech (Fagus orientalis L.) with cross sections and tenon sizes identical to those used in the chairs were first determined. Tenons varied from 30, 40, and 50 mm in width and 30, 40, and 50 mm in length. Joints were assembled with 65% solid polyvinylacetate (PVAc) adhesives. Front to back loading tests were then performed on the chairs according to the method adopted by the American Library Association (ALA). The results indicated that front to back loading capacity increases as either tenon width or length increases. Highest joint moment capacities were obtained when L-shaped joints were constructed with 50 mm wide by 50 mm long tenons and T-shaped joints were constructed with 40 mm wide by 50 mm long tenons. Finally, the strength of chairs could be reasonably predicted from the strength of joints.

Optimal Residential Load Management in Smart Grids: A Decentralized Framework

Severe peak rebounds are likely in absence of a system-wide coordination among customers participating in demand response programs. This paper aims to establish a decentralized system-wide framework to coordinate demand response of residential customers in a smart grid. The objective of the framework is to modify system load profile provided that customers’ payments are minimized, and their comfort and privacy are preserved. Home load management (HLM) modules, embedded in customers’ smart meters are autonomous agents of the framework. The energy service provider iteratively exchanges load information with HLM modules in the hope of achieving his desired load profile. In each iteration, the service provider announces system load profile to HLM modules. The modules, keeping in mind their own financial and comfort constraints, nonsequentially send back load reschedule proposals to modify system load profile. The received proposals are judged whether they improve system load profile or not. HLM modules with accepted proposals apply their proposed schedules. The modified system load profile is then released, and HLM modules’ new proposals are gathered and judged. This procedure is repeated to the point at which no further improvement in the system load profile can be experienced. Performance of the framework is shown by applying it to a system with 50 customers.

Course Setting as a Prevention Measure for Overuse Injuries of the Back in Alpine Ski Racing: A Kinematic and Kinetic Study of Giant Slalom and Slalom.

Background:A combination of frontal bending, lateral bending, and torsion in the loaded trunk has been suggested to be a mechanism leading to overuse injuries of the back in Alpine ski racing. However, there is limited knowledge about the effect of course setting on the aforementioned back-loading patterns.Purpose:To investigate the effect of increased gate offset on the skier’s overall trunk kinematics and the occurring ground-reaction forces and to compare these variables between the competition disciplines giant slalom (GS) and slalom (SL).Study Design:Controlled laboratory study.Methods:Ten top-level athletes were divided into GS and SL groups. Both groups performed a total of 240 GS and 240 SL turns at 2 different course settings. The overall trunk movement components (frontal bending, lateral bending, and torsion angle) were measured using 2 inertial measurement units fixed on the sacrum and sternum. Total ground-reaction forces were measured by pressure insoles.Results:In SL, ground-reaction force peaks were significantly lower when the gate offset was increased, while in GS, no differences between course settings were observed. During the turn phase in which the highest spinal disc loading is expected to occur, the back-loading patterns in both GS and SL included a combination of frontal bending, lateral bending, and torsion in the loaded trunk. SL was characterized by shorter turns, lower frontal and lateral bending angles after gate passage, and a trend toward greater total ground-reaction force peaks compared with GS.Conclusion:Course setting is a reasonable measure to reduce the skier’s overall back loading in SL but not in GS. The distinct differences observed between GS and SL should be taken into account when defining discipline-specific prevention measures for back overuse injuries.Clinical Relevance:To reduce the magnitude of the overall back loading, in SL, minimal gate offsets should be avoided. Prevention measures in GS might particularly need to control and/or reduce the magnitude of frontal and lateral bending in the loaded trunk, whereas prevention measures in SL might especially need to mitigate the short and high total ground-reaction force peaks.