Assessing the ergonomic exposures for drywall workers

Objective

The study was conducted to assess the ergonomic exposures to risk factors that may lead to the reported musculoskeletal injuries (especially back, neck and wrist injuries) of drywall workers.

Methods

A hierarchical taxonomy for construction of drywall panel hanging (drywall panel fitting and installation) was developed with activities defined within the interior wall systems tasks (drywall panel, studs and insulation). Exposures were characterized for the drywall panel work with the PATH (Posture, Activity, Tools, and Handling) work-sampling observation method. Data on working postures were collected for three main body parts: legs, arms and trunk. Activities performed for each task, tools used, and manually handled loads were also recorded for each observation.

Results

The study identified several ergonomic exposures in interior systems construction. Several risk factors were especially prevalent in the drywall panel installation task: awkward body postures such as overhead arm posture, trunk flexion, and handling of heavy drywall panels. Some tasks were observed to have combinations of these musculoskeletal risk factors, such as drywall panel installation, where the workers lifted heavy drywall panels in awkward body postures. In addition, a safety hazard frequently resulted when a worker's foot was poorly supported on a ladder while lifting heavy drywall panels to hang them on the ceiling or upper wall.

Conclusion

The drywall panel installation task poses a severe threat to the safety and musculoskeletal health of the drywall workers. Much of this could be eliminated by reducing the burden of handling heavy and bulky drywall panels.

Relevance to industry

The construction industry is well-documented to have high rates of injury and musculoskeletal disorders. Design of appropriate interventions requires specific knowledge of which tasks and activities involve the highest levels of exposure to relevant factors. Assessment of such factors in drywall panel hanging has provided data that will be useful to evaluate the ergonomics efficacy of future changes in task processes or tools. Feasible solutions appear to exist; effectiveness trials and worker input are needed in order to evaluate whether they could eliminate the observed exposures.     

The effect of pallet distance on torso kinematics and low back disorder risk

Intervention research for prevention of occupational low back injuries has focused on the effects of reducing extreme torso flexion and the external moment. Little is known about prevention strategies for torso twisting and lateral bending. The objective of this study was to assess the effect of pallet distance with regard to a constant lift origin on the torso kinematics and a measure of low back disorder risk. Fifteen male participants transferred 11.3?kg boxes from a constant origin to six different regions on a pallet. Two pallet distances with regard to the lift origin were investigated. ANOVA indicated that increasing the pallet distance resulted in increases in torso kinematics (velocities and accelerations) as well as a measure of risk of low back disorder. The increases in torso kinematics (e.g. twisting and lateral awkward postures and bending velocities) occurred mostly at the lower height regions on the pallet. It is concluded that increasing the pallet distance with regard to the lifting origin, with the intention to influence the participant to take a step during a palletizing task does not appear to be an effective intervention strategy to reduce the risk of low back disorder associated with torso kinematics.     

The effect of pallet distance on torso kinematics and low back disorder risk

Intervention research for prevention of occupational low back injuries has focused on the effects of reducing extreme torso flexion and the external moment. Little is known about prevention strategies for torso twisting and lateral bending. The objective of this study was to assess the effect of pallet distance with regard to a constant lift origin on the torso kinematics and a measure of low back disorder risk. Fifteen male participants transferred 11.3 kg boxes from a constant origin to six different regions on a pallet. Two pallet distances with regard to the lift origin were investigated. ANOVA indicated that increasing the pallet distance resulted in increases in torso kinematics (velocities and accelerations) as well as a measure of risk of low back disorder. The increases in torso kinematics (e.g. twisting and lateral awkward postures and bending velocities) occurred mostly at the lower height regions on the pallet. It is concluded that increasing the pallet distance with regard to the lifting origin, with the intention to influence the participant to take a step during a palletizing task does not appear to be an effective intervention strategy to reduce the risk of low back disorder associated with torso kinematics.     

Occupational lifting by nursing aides and warehouse workers

Nursing aides (18 women and six men) at one traditional and one modern geriatric ward, and warehouse workers (16 men) at two different types of warehouse departments were studied during occupational work. The vertical load during manual handling was measured using strain gauges built into wooden shoes. The warehouse workers performed four times as many lifts as the nursing aides and transferred five times as great a mass per unit time. Less than 25% of the lifts were carried out with the load evenly distributed on both feet during both the upward lift and lowering. In the warehouses the lifts were short, while the nursing aides were exposed both to lifts of longer duration and to carrying, as well as a greater frequency of unexpected, sudden and high peak load. The heart rate and oxygen uptake values recorded were relatively low, and both groups utilized approximately 25% of their maximum aerobic power. According to official occupational injury statistics, both warehouse workers and nursing aides belong to risk groups with a high frequency of reported back injuries. However, more injuries are reported by nursing aides than by warehouse workers. Greater muscle strength in male workers may partly explain this difference. Qualitative differences in the design of the lifting work, with more lifts of long duration in awkward work postures, more carrying, more exertion of horizontal forces and a greater frequency of unexpected rapid lifts in the nursing aides may also contribute to the differences in risk of injury between these occupational groups. Considerable differences were found between the two hospital wards as regards lifting frequency, force, duration and the proportion of lifts with an even distribution of load on both feet during upward lift. The lifting work was approximately 50% less in the modern ward, which has easily maneuvered electric overhead hoists, spacious premises and better work organization than in the traditional ward, even though the patient handling needs were equivalent. In the warehouse department at which the wares were stored with easy access, the frequency of lifts with an even distribution of load on both feet was approximately 25%, compared to 7% in the other warehouse department. In conclusion, evaluations of occupational lifting work should include a quantitative assessment of the duration and load distribution of lifting, as well as of postures. Workstation design, technical aids and work organization have a profound effect on the lifting work load even in jobs with equal manual handling demands.     

External L5–S1 joint moments when lifting wire mesh screen used to prevent rock falls in underground mines

Bolting large sheets of wire mesh screen (WMS) to the roof of underground mines prevents injuries due to rock falls. However, WMS can be heavy and awkward to lift and transport, and may result in significant spinal loading. Accordingly, six male subjects (mean age = 45.8 years + 7.5 SD) were recruited to lift WMS in a laboratory investigation of the biomechanical demands. Biomechanical modeling was used to estimate external moments about L5–S1 for sixteen lifting tasks, using two sizes of WMS. Full-size WMS involved a two-person lift, while half-size WMS involved a one-person lift. Lifts were performed under 168 cm and 213 cm vertical space. Restriction in vertical space increased the maximum L5–S1 extensor moment from 254 to 274 Nm and right lateral bending moment from 195 to 251 Nm. Lifting full sheets of screen (as opposed to half sheets) resulted in an average 33 Nm increase in L5–S1 extensor moment. The L5–S1 extensor moment was increased by an average of 44 Nm (18%) when lifting screens positioned flat on the floor compared to an upright position.

Relevance to industry

Large flexible materials are commonly lifted in industrial work environments, and may involve the efforts of two or more workers. The current study examines the low back loading associated with lifting large flexible screens and presents recommendations to reduce spine loading.     

A biomechanical and ergonomic evaluation of patient transferring tasks: wheelchair to shower chair and shower chair to wheelchair.

A laboratory study was conducted to evaluate five different manual techniques (two-person manual lifting; rocking and pulling the patient using a gait belt with two persons; walking belt with one and two persons) and three different mechanical hoists (Hoyer lift, Trans-Aid and Ambulift) for transferring patients from wheelchair to shower chair and shower chair to wheelchair. Six female nursing students with prior patient transfer experience served both as nurses and as passive patients. Static biomechanical evaluation showed that the mean trunk flexion moments, erector spinae muscle forces and compressive and shear forces at the L5S1 disc for the four pulling methods ranged from 92 to 125 Nm, 1845 to 2507 N, 1973 to 2641 N and 442 to 580 N, respectively, as compared to about 213 Nm, 4260 N, 5050 N and 926 N for two-person manual lifting. Perceived stress ratings for the shoulder, upper back, lower back and whole body were significantly lower for pulling methods than those for lifting the patient (p less than or equal to 0.01). Patients found pulling techniques, except the gait belt, to be more comfortable and secure than the lifting method (p less than or equal to 0.01). However, most of the nurses believed that Medesign and the one-person walking belt would not work on those patients who cannot bear weight and those who are heavy, contracted or combative. A two-person walking belt was the most preferred method. Two out of three hoists (Hoyer lift and Trans-Aid) were perceived by the nurses to be more stressful than one- and two-person walking belts. The patients found these two hoists to be more uncomfortable and less secure than with three of the five manual methods (one- and two-person walking belts and Medesign). Pulling techniques and hoists took significantly longer amounts of time to make the transfer than manually lifting the patient (p less than or equal to 0.01). The two-person walking belt, using a gentle rocking motion to utilize momentum and a pulling technique, and Ambulift are recommended for transferring patients from wheelchair to shower chair and shower chair to wheelchair.     

Work activities and musculoskeletal complaints among preschool workers

The potential for musculoskeletal trauma among preschool workers has been largely unexplored in the United States. This case report describes an investigation conducted to identify and evaluate possible causes of back and lower extremity pain among 22 workers at a Montessori day care facility. Investigators met with and distributed a questionnaire to school employees, and made measurements of workstation and furniture dimensions. Investigators also recorded the normal work activities of school employees on videotape, and performed a work sampling study to estimate the percentage of time employees spend performing various tasks and in certain postures.

Questionnaire results from 18 employees indicated that back pain/discomfort was a common musculoskeletal complaint, reported by 61% of respondents. Neck/shoulder pain, lower extremity pain and hand/wrist pain were reported by 33, 33 and 11% of respondents, respectively. Observation and analysis of work activities indicated that employees spend significant periods of time kneeling, sitting on the floor, squatting, or bending at the waist. Furthermore, staff members who work with smaller children (i.e. six weeks to 18 months of age) performed more lifts and assumed more awkward lower extremity postures than employees who work with older children (3–4 years of age). Analysis of two lifting tasks using the revised NIOSH lifting equation indicated that employees who handle small children may be at increased risk of lifting-related low back pain. Investigators concluded that day care employees at this facility are at increased risk of low back pain and lower extremity (i.e. knee) injury due to work activities that require awkward or heavy lifts, and static working postures. Recommendations for reducing or eliminating these risks by modifying the workplace and changing the organization and methods of work are presented.     

An evaluation of patient lifting techniques

Abstract

In the present laboratory study five two-person manual lifting techniques were evaluated as to the amount of physical exertion required of the nurses. Ten female volunteers served as nurses; two healthy volunteers (weight: 55 kg and 75 kg) served as passive patients. The working postures and motions were recorded on videotape. The data thus obtained were used in a anatomical-biomechanical analysis. The perceived exertion by the nurses was measured as well. In almost all situations the compressive forces on the nurse's spine exceeded their acceptable limit of 3425 N. Differences between the lifting techniques were most obvious when the 55 kg patient was lifted. Ratings of the perceived exertion (RPE scores) were higher in symmetrical handling than in asymmetrical handling. The three techniques using asymmetrical hand positions produced less subjective stress. RPE scores and rotation of the back were negatively correlated. Rotating the back when moving a patient from one side to the other seems to ease the task. On the whole, the results of the biomechanical evaluation are in line with the subjective perception of the nurses. In both instances the barrow lift appeared to be the most strenuous one; the Australian lift resulted in low compressive forces and a moderate level of perceived exertion     

Ergonomic assessment for designing manual material handling tasks at a food warehouse in India: A case study

Manual handling of heavy grain bags is a commonplace activity across agriculture produce supply chain. In the present research, a manual material handling involving lifting, lowering, and carrying grain bags along the paths of variable characteristics is critically analyzed to explore the risk associated with it. The humans engaged in this activity are found to be facing discomfort, suffering from pain and musculoskeletal disorders, and undergoing medication for the same. This study proposes and demonstrates a structured ergonomic evaluation methodology to not only assess the level of discomfort/pain but also evaluate risk factors such as load handled, method of handling, frequency of handling, awkward postures, path characteristics, and so on. It employs a systematic multimethod approach consisting of Nordic Musculoskeletal Questionnaire and Borg Rating of Perceived Exertion, Ovako Working posture Assessment System, NIOSH Lifting Equation, Rapid Entire Body Assessment, and Key Indicator Method. The study reveals that about 94% of the sample population suffered from moderate to severe discomfort in ankle, knee, and lower back. Eight basic activities responsible for risky postures are identified. Frequency of handling, weight being handled, back bending/twisting, poor coupling, and walking surface are observed as major contributors to musculoskeletal discomfort. Carrying on shoulder is found to be riskier than carrying on back; however, the risk is found to be significantly lowered by carrying on backpack. The present study identifies the need for task redesign, proper gripping arrangements, auxiliary devices for lifting/carrying, and improvement in the path characteristics.     

Biomechanical evaluation of nursing tasks in a hospital setting

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

A biomechanical and ergonomic evaluation of patient transferring tasks: bed to wheelchair and wheelchair to bed.

A laboratory study was conducted in an effort to reduce back stress for nursing personnel while performing the patient handling tasks of transferring the patient from bed to wheelchair and wheelchair to bed. These patient handling tasks were studied using five manual techniques and three hoist-assisted techniques. The manual techniques involved one-person and two-person transfers. One manual technique involved a two-person lift of the patient under the arms; the others used a rocking and pulling action and included the use of assistive devices (a gait belt using a two-person transfer, a walking belt with handles using a one-person and a two-person transfer, and a patient handling sling with cutout areas to allow for a hand grip (Medesign) for a one-person transfer). The three mechanical hoists were Hoyer, Trans-Aid and Ambulift. Six female nursing students with prior patient transfer experience served both as nurses and as passive patients. Static biomechanical evaluation showed that pulling techniques, as compared to lifting the patient, required significantly lower hand forces and produced significantly lower erector spinae and compressive forces at the L5/S1 disc (P greater than or equal to 0.01). Shear force, trunk moments and the percentage of females who were capable of performing the transfers (based on static strength simulation) also favoured pulling methods. Perceived stress ratings for the shoulder, upper back, lower back and whole body were lower for pulling methods than those for lifting the patient (P less than or equal to 0.01). Patients found the pulling techniques, with the exception of when using the gait belt, felt more comfortable and more secure than the lifting method (P less than or equal to 0.01). However, a number of subjects believed that the patient handling sling (Medesign) and the walking belt with one person making the transfer would not work for those patients who could not bear weight and those who were heavy, contracted or combative. A walking belt with two persons was the preferred manual method. Two out of three hoists (Hoyer lift and Trans-Aid) were perceived by the nurses to be as physically stressful as manual methods. Patients found these two hoists to be more uncomfortable and felt less secure than with three of the five manual methods (one- and two-person walking belts and Medesign). Ambulift was found to be the least stressful, the most comfortable, and the most secure among all eight methods. Pulling techniques and hoists took significantly longer amounts of time to make the transfer than manually lifting the patient (P less than or equal to 0.01). The two-person walking belt using a pulling technique and Ambulift are recommended for transferring patients from bed to wheelchair and wheelchair to bed. A large-scale field study is needed to verify these recommendations.     

Potential of adjustable height carts in reducing the risk of low back injury in grocery stockers

While the workers of the Wholesale and Retail Trade industrial sector suffer from musculoskeletal disorders at an alarming rate, there have been few investigative studies into potential effective interventions to reduce the ergonomic stress. The objective of the study was to determine whether a cart with an adjustable shelf could reduce awkward postures and motions while stocking products in a grocery store. Fifteen workers at a small grocery store in Puerto Rico completed stocking tasks with two types of carts: traditional and adjustable height cart or Ergo Cart. Trunk kinematics, LBD risk index, NIOSH lifting index, subjective ratings, and productivity indicators were collected during four typical stocking tasks. The Adjustable Ergo Cart reduced the sagittal trunk flexion by 7° and velocity by about 5°/s but increased twisting by about 2° and twist velocity by 4°/s as compared to the traditional cart. The LBD risk index was reduced by a small 2.4% in probability although greater reductions were found for larger items (e.g. bags of dog food and 2-L of Soda). The consensus among workers was that the adjustable cart would be easier to use. Overall, the study provides objective evidence that an ergonomically designed cart (e.g. adjustable height) has some potential to reduce sagittal trunk flexion, LBD risk index, and the NIOSH lift index. Overall, the results indicate that any intervention such as an adjustable cart can only have marginal effectiveness unless the entire systems perspective is considered.     

Significance of biomechanical and physiological variables during the determination of maximum acceptable weight of lift

The aim was to identify which biomechanical and physiological variables were associated with the decision to change the weight of lift during the determination of the maximum acceptable weight of lift (MAWL) in a psychophysical study. Fifteen male college students lifted a box of unknown weight at 4.3 lifts/min, and adjusted the weight until their MAWL was reached. Variables such as heart rate, trunk positions, velocities and accelerations were measured during the lifting, as well as estimated spinal loading in terms of moments and spinal forces in three dimensions using an EMG-assisted biomechanical model. Multiple logistic regression techniques identified variables associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that heart rate, predicted sagittal lift moment and low back disorder (LBD) risk index were associated with decreases in the weight prior to the next lift. Thus, historical measures of LBD risk (e.g. compression, shear force) were not associated with decreases in weight prior to the next lift. Additionally, the magnitudes of the predicted spinal forces and LBD risk were all very high at the MAWL when compared with literature sources of tolerance as well as observational studies on LBD risk. Our findings indicate that the psychophysical methodology may be useful for the decision to lower the weight of loads that may present extreme levels of risk of LBD; however, the psychophysical methodology does not seem to help in the decision to stop changing the weight at a safe load weight.     

Significance of biomechanical and physiological variables during the determination of maximum acceptable weight of lift.

The aim was to identify which biomechanical and physiological variables were associated with the decision to change the weight of lift during the determination of the maximum acceptable weight of lift (MAWL) in a psychophysical study. Fifteen male college students lifted a box of unknown weight at 4.3 lifts/min, and adjusted the weight until their MAWL was reached. Variables such as heart rate, trunk positions, velocities and accelerations were measured during the lifting, as well as estimated spinal loading in terms of moments and spinal forces in three dimensions using an EMG-assisted biomechanical model. Multiple logistic regression techniques identified variables associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that heart rate, predicted sagittal lift moment and low back disorder (LBD) risk index were associated with decreases in the weight prior to the next lift. Thus, historical measures of LBD risk (e.g. compression, shear force) were not associated with decreases in weight prior to the next lift. Additionally, the magnitudes of the predicted spinal forces and LBD risk were all very high at the MAWL when compared with literature sources of tolerance as well as observational studies on LBD risk. Our findings indicate that the psychophysical methodology may be useful for the decision to lower the weight of loads that may present extreme levels of risk of LBD; however, the psychophysical methodology does not seem to help in the decision to stop changing the weight at a safe load weight.     

Spine loading and trunk kinematics during team lifting

Two-person or team lifting is a popular method for handling materials under awkward or heavy lifting conditions. While many guidelines and standards address safe lifting limits for individual lifting, there are no such limits for team lifting, and these lifts are poorly understood. The literature associated with team lifting offers some interesting paradoxes. Many studies have indicated that people lift less per individual under team conditions compared with one-person lifting. Yet, at least one study has reported an increase in team-lifting capacity when subjects were height-matched. The current study explored the spine loading characteristics of one- and two-person lifting teams when subjects lifted under several sagittally symmetric and asymmetric conditions. Spine compression was lower for two person lifts for a given weight, while lifting in sagittally symmetric conditions whereas lateral shear became much greater for two-person lifts under asymmetric lifting conditions. This study has linked these changes to differences in trunk kinematic patterns adopted during one- versus two-person lifting.     

Spine loading and trunk kinematics during team lifting

Two-person or team lifting is a popular method for handling materials under awkward or heavy lifting conditions. While many guidelines and standards address safe lifting limits for individual lifting, there are no such limits for team lifting, and these lifts are poorly understood. The literature associated with team lifting offers some interesting paradoxes. Many studies have indicated that people lift less per individual under team conditions compared with one-person lifting. Yet, at least one study has reported an increase in team-lifting capacity when subjects were height-matched. The current study explored the spine loading characteristics of one- and two-person lifting teams when subjects lifted under several sagittally symmetric and asymmetric conditions. Spine compression was lower for two person lifts for a given weight, while lifting in sagittally symmetric conditions whereas lateral shear became much greater for two-person lifts under asymmetric lifting conditions. This study has linked these changes to differences in trunk kinematic patterns adopted during one- versus two-person lifting.     

Analysis of biomechanical stresses during drywall lifting

Constant lifting of massive and bulky drywall sheets creates overexertion hazards among drywall installers. The objective of this study was to gain understanding of the biomechanical stresses imposed on the workers while lifting drywall sheets. A video analysis was performed to identify current drywall lifting techniques. Computer simulations of these techniques for lifting drywall sheets of 60, 80, and 100 lb were then conducted to estimate the biomechanical loadings on the workers. Four lifting methods were determined to be the most commonly used drywall lifting techniques. The University of Michigan Three-Dimensional Static Strength Prediction Program (3DSSPP^TM) was used for the simulations. It was found that all four lifting techniques produced considerable biomechanical stresses at the workers' shoulders, torsos, and hips. Only a limited percentage of the male population has sufficient strength capability to perform the task. The estimated L5/S1 and L4/L5 disc compression forces were consistently high, ranging from 655 to 1363 lb for various loads and postures analyzed. Results from this study provided evidence regarding the biomechanical stresses associated with drywall lifting. Further studies are recommended to identify less stressful drywall lifting methods and to develop safe assistive devices to reduce overexertion injuries.

Relevance to industry

There is an increasing tendency toward awareness of ergonomic issues in the construction industry. One area of the construction industry – drywall installation – has been troubled with overexertion injuries. Lifting massive and bulky drywall sheets increases the risk of overexertion injuries. Prior to this study there has been little substantive research to quantify the excessive stresses imposed on drywall installers.     

The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting

There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10° and 20°), two declined surfaces (facing a downward slope: ? 10° and ? 20°), and a flat surface (0°) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.     

The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting

There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10 degrees and 20 degrees), two declined surfaces (facing a downward slope: -10 degrees and -20 degrees), and a flat surface (0 degrees) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.     

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

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