Physiological effects of back belt wearing during asymmetric lifting

This study investigated the effect of wearing a back belt on subjects' heart rate, oxygen consumption, systolic and diastolic blood pressure, and respiratory frequency during asymmetric repetitive lifting. Thirty subjects with materials-handling experience utilized three different belts (ten subjects per belt). Subjects completed six 30-min lifting sessions--three while wearing a belt and three without. Data analyses were conducted on the second, third, and fourth lifting periods. A 9.4 kg box, without handles, was lifted 3 times/min, starting at 10 cm above the floor, ending at 79 cm, with a 60 degree twist to the right. Data analysis indicates that belt-wearing did not have a significant effect on the overall mean values for heart rate, systolic and diastolic blood pressure, and respiratory frequency. Belt-wearing had a significant effect on the overall mean oxygen consumption of the subjects.     

Development and evaluation of an affordable lift device to reduce musculo-skeletal injuries among home support workers

Home support workers (HSWs) work in clients' homes assisting with rehabilitation and activities of daily living. Like all health-care professionals, HSWs are at an increased risk for developing back injuries. Lift devices have been shown to reduce injuries to the worker. Presently, there are few lifting devices for home use that cost under $4000 CDN. Our study involved designing a safe and affordable lift device (retail cost under $2000 CDN) to be used by HSWs in the home and evaluating it in a typical bathroom. Thirty-eight HSWs and three seniors evaluated the BCIT lift, a commercially available lift (BHM Medical Inc.) and the manual method of transfer and lift. Results indicated that the BCIT lift was an improvement over the manual method of transferring, and approximated the more expensive, automatic lift in terms of perceived exertion, ease of use and safety. Feedback provided to the researchers has been incorporated into a new, ergonomically sound and marketable lift device.     

The functional evaluation of a back belt rehabilitation for low-back pain patients

Back belts are used for preventative and therapeutic purposes. The outcome measures fail to support the use of back belts to treat or prevent back injuries. The purposes of this study were (1) to estimate the reliability and responsiveness of the health outcome for individuals participating in back belt rehabilitation, and (2) to compare the health-related quality of life between individuals with low-back pain (LBP) and normal subjects. Twenty-three volunteers without any complaint of LBP and 95 LBP patients participated in this study. The mobility test and the SF-36 provide reliable and responsive measurements, but they appear to provide different information about the health status of LBP patients. Compared with normal subjects, LBP patients had lower scores for health-related quality of life, but these scores improved after 12 weeks of back belt rehabilitation.

Relevance to industry

A clinically based outcome measure can provide a reliable and responsive tool for the routine assessment of perceived health in patients undergoing back belt rehabilitation. This evaluation program will be continuously used to screen workers using back belts for successful back injury prevention.     

Lifting belts: a psychophysical analysis

The literature supporting the use of lifting belts has not demonstrated consistent trends. It was hypothesized that if lifting belts provide a biomechanical or motivational advantage then the participants in a psychophysical lift test should select a higher maximum acceptable weight of lift (MAWL). Eleven male and five female subjects participated in one session with a lifting belt and one session without a belt. The order of the belt sessions was counterbalanced. Each session was comprised of two psychophysical lifting tests varying only in the initial weight of the box. Repeated measures ANOVA showed no difference between the MAWL between belt sessions or between the two tests within a given session. Following the test, subjective evaluations of the belt were measured via a questionnaire. The psychophysical test results showed no change as a function of the belt condition. Thus, these results do not support the hypothesis that lifting belts increase trunk strength or motivate individuals to select a greater MAWL. Therefore, it must be concluded that belts do not offer a biomechanical or motivational advantage to the user.     

Workplace design guidelines for asymptomatic vs. low-back-injured workers

While numerous efforts have attempted to provide quantitative guidelines for the prevention of initial low back disorders during material handling tasks, none have appeared in the literature that address the issue of recurrent low back disorders due to materials handling when returning to the workplace. A study comparing the spine loads of low back pain patients and asymptomatic controls was conducted. Subjects lifted weights varying from 4.5-11.4 kg at four vertical heights, two horizontal distances and five task asymmetries collectively representing common industrial lifting situations. Spine loading was calculated using a validated EMG-assisted biomechanical model. Spine loads observed during lifting tasks were compared to spine tolerance values believed to initiate low back injuries. In addition, the percentage of patients successfully performing the lift was noted and used as an indication of the willingness of the subject to perform the task. These evaluations are summarized in a series of three lifting guidelines indicating safe, medium risk and high risk lifting tasks for low back patients as well as asymptomatic workers. It is believed that adherence to these guidelines can minimize the risk of recurrent low back disorders due to occupational lifting.     

Review of: “ Systems Documentation: Techniques of persuasion in large organizations”. By FRANK WHITEHOHSE, ( London: Business Books, 1973.) [Pp. viii + 191.] £450.

The use of back belts in industry has increased despite the lack of scientific evidence supporting their efficacy. The purpose of this study was to investigate the effect of a semi-rigid lumbosacral orthosis (SRLSO) on oxygen consumption during 6-min submaximal repetitive lifting bouts of 10 kg at a lifting frequency of 20 repetitions min^-1. Fifteen healthy subjects (13 men, two women) participated in this study. Each subject performed squat and stoop lifting with and without an SRLSO for a total of four lifting bouts. Lifting bouts were performed in random order. Oxygen consumption during the final minute of each lifting bout was used for analysis. A two-way analysis of variance with repeated measures was used to analyse the effects of lift and belt conditions. The stoop and squat methods were significantly different, with the squat lift requiring 23% more oxygen on average than the stoop lift for equal bouts of work. No significant difference was found between the belt and no belt condition within the same lifting technique and no interaction was present. These data suggest that an SRLSO does not passively assist the paravertebral muscles (PVM) in stabilizing the spine during submaximal lifting bouts.     

The force-velocity relation and intra-abdominal pressure during lifting activities

An experiment was performed to test the static and dynamic lifting capabilities of the back. Twenty healthy male and female subjects exerted maximal force with the back under isometric and isokinetic lifting positions. Torque about the lumbosacral junction and intra-abdominal pressure (IAP) production were monitored under the experimental conditions. Torque production capability was found to increase as trunk angle increased and decreased as angular velocity increased. IAP was found to be primarily a funciton of angle and a weak indicator of torque. A significant IAP-torque onset delay was identified as was a physiological source of IAP.     

When is a lifting movement too asymmetric to identify lowback loading by 2-D analysis?

In ergonomics research, two-dimensional (2-D) biomechanical models are often used to study the mechanical loading of the low back in lifting movements. When lifting movements are asymmetric, errors of unknown size may be introduced in a 2-D analysis. In the current study, an estimation of these errors was made by comparing the outcome of a 2-D analysis to the results of a recently developed and validated 3-D model. Four subjects made two repetitions of five lifting movements, differing in the amount of asymmetry. The results showed a significant underestimation of the peak torque by 20, 36 and 61% when the initial position of a box was rotated 30, 60 and 90 with respect to the sagittal plane of the subject. The main cause of this underestimation was a pelvic twist, resulting in an erroneous projection of a pelvic marker on to the sagittal plane due to pelvic twist. It is suggested that from 30 box rotation a 2-D analysis may easily lead to wrong conclusions when it is used to study asymmetric lifting.     

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.     

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.     

Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions

The aim of this study was to assess the effect of an elastic lumbar back support on spinal loading and trunk, hip and knee kinematics while allowing subjects to move their feet during lifting exertions. Predicted spinal forces and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerations, and hip and knee angles were evaluated as a function of wearing an elastic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), and from two different asymmetries at the start of the lift (sagittally symmetric and 60 degrees asymmetry). Subjects were allowed to lift using any lifting style they preferred, and were allowed to move their feet during the lifting exertion. Wearing a lumbar back support resulted in no significant differences for any measure of spinal loading as compared with the no-back support condition. However, wearing a lumbar back support resulted in a modest but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7 degrees), as well as reduction in the sagittal trunk extension velocity (47.2 to 40.2 degrees s(-1)). Thus, the use of the elastic lumbar back support provided no protective effect regarding spinal loading when individuals were allowed to move their feet during a lifting exertion.     

Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions

The aim of this study was to assess the effect of an elastic lumbar back support on spinal loading and trunk, hip and knee kinematics while allowing subjects to move their feet during lifting exertions. Predicted spinal forces and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerations, and hip and knee angles were evaluated as a function of wearing an elastic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), and from two different asymmetries at the start of the lift (sagittally symmetric and 60°asymmetry). Subjects were allowed to lift using any lifting style they preferred, and were allowed to move their feet during the lifting exertion. Wearing a lumbar back support resulted in no significant differences for any measure of spinal loading as compared with the no-back support condition. However, wearing a lumbar back support resulted in a modest but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7°), as well as reduction in the sagittal trunk extension velocity (47.2 to 40.2°s^-1). Thus, the use of the elastic lumbar back support provided no protective effect regarding spinal loading when individuals were allowed to move their feet during a lifting exertion.     

Do workplace interventions prevent low-back disorders? If so,why?: a methodologic commentary

The demand for workplace interventions to prevent low-back disorders has increased in recent years. At the same time, a crisis in the literature has become apparent: there are conflicting reports on whether or not these interventions work. With the aim of understanding the reason for the dissension in the literature, six studies were selected for close examination. These were studies of interventions based on differing principles, i.e. a change in organizational ethos to promote back safety, back belt use, the introduction of ergonomic devices, and back-strengthening exercises. If the studies are taken at face value, any of the interventions, regardless of type, has a tremendous effect. Methodological problems inherent in these studies may provide a clue to why essentially different interventions were found to be consistently successful. Study design quality has long been noted to exert a particular influence on the evaluation of outcomes: the quality of the study design is often inversely related to reported outcomes. Of the six studies selected for examination, four did not include a contemporaneous control group, five did not randomly assign subjects to test and control groups, and none included a placebo group. Given these research designs, variables other than those tested by the studies may have produced the reported results. These variables include ‘beliefs of the intervention providers’ and ‘coalescence of the work group ’, both of which are discussed. Two approaches, the pragmatic and the explanatory, may be used to study workplace interventions to prevent low-back disorders. Most of the examined studies are pragmatically oriented. Having dealt with study design problems expeditiously, these studies may be characterized as more immediately responsive to the demand to evaluate workplace interventions than explanatory studies. On the other hand, explantory studies, most notably associated with randomized clinical trials in medicine, are more rigorous. Enough pragmatically oriented studies have been conducted to suggest that workplace interventions may have an effect on low-back disorders. More conclusive explanatory studies may now be conducted.     

The effect of a lower extremity kinematic constraint on lifting biomechanics

Leaning against a stationary barrier during manual materials handling tasks is observed in many industrial environments, but the effects of this kinematic constraint on low back mechanics are unknown. Thirteen participants performed two-handed lifting tasks using both a leaning posture and no leaning posture while trunk kinematics, muscle activity and ground reaction force were monitored. Results revealed that lifting with the leaning posture required significantly less activity in erector spinae (26% vs. 36% MVC) and latissimus dorsi (8% vs. 14% MVC), and less passive tissue moment compared with the no leaning posture. Peak sagittal accelerations were lower when leaning, but the leaning posture also had significantly higher slip potential as measured by required coefficient of friction (0.05 vs. 0.36). The results suggested that the leaning lifting strategy provides reduced low back stress, but does so at the cost of increased slip potential.     

Using sitting as a component of job rotation strategies: Are lifting/lowering kinetics and kinematics altered following prolonged sitting

Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering exertions following extended seated exposures. Upper body kinematics, lumbar spine flexion angle, pelvic orientation and bilateral muscle activity from the external abdominal obliques and lumbar erector spinae were recorded for 8 males and 8 females while they alternated between sessions of repetitive lifting/lowering and prolonged sitting. Upper body kinematics were used as inputs to a linked segment model to compute low-back flexion/extension moments, compression, and shear. Peak lumbar flexion was reduced by 1.8° during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50 N in the reaction anteroposterior shear forces. Sitting postures were consistent with previously reported data. The reduced shear loads during repetitive lift/lower exertions following prolonged sitting may be a consequence of alterations in passive tissue properties which could alter the risk of low-back injury, although future research is required to examine the biomechanical significance of this finding. Changes to both kinematics and kinetics were minimal suggesting that using prolonged sitting as a component of a task series in job rotation does not alter the risk present when combined with repetitive lifting tasks.     

Comparing standing posture and use of a sit-stand stool: Analysis of vascular,muscular and discomfort outcomes during simulated industrial work

Sit-stand stools are available for use in industrial settings, but there is a lack of quantitative evidence demonstrating benefits for lower limb, back and/or neck/shoulder outcomes. In this paper we describe an experiment conducted to compare and contrast posture and time-related differences in muscular and vascular outcomes during 34 min of manual repetitive work performed in either standing or sit-standing work posture. We measured vascular parameters in the lower limbs, and muscular parameters in the trunk and neck/shoulder, and discomfort in the three regions as participants accomplished a repetitive box-folding task. Results show that blood flow in the foot (p = 0.022) and ankle mean arterial pressure (p < 0.001) were greater during standing. Left gluteus medius and external oblique activation was higher during standing, while sit-standing work resulted in higher levels of co-activation between the left erector spinae and external oblique muscle pair (p = 0.026). Neck/shoulder muscle activity was not significantly different between the conditions. Reported discomfort did not differ significantly for the trunk and neck/shoulder region, but standing resulted in higher level of reported discomfort in the lower limb. The sit-stand posture used in this experiment appears to prevent the undesirable lower limb outcomes associated with static standing work posture.Relevance to industryThis work demonstrates quantitative evidence to support the potential use of a sit-stand stool for industrial work operations, at least over relatively short durations.     

Empirical evaluation of training and a work analysis tool for participatory ergonomics

A controlled laboratory experiment was performed to test the effects of ergonomics training and the NIOSH lifting equation on the participatory redesign of a simulated manual material handling job. Before performing the job, 16 subjects were given ergonomics training and 16 were instructed on how to use the NIOSH lifting equation for manual lifting tasks. Compared to a control group, subjects who received the ergonomics instruction identified and eliminated more risk factors in the simulated job. While subjects who used the NIOSH lifting equation also identified more risk factors, they did not eliminate any more risk factors than the control group. No additive benefit was found using both the training and the lifting equation over either method alone. Ergonomics training led to better improvements than use of the lifting equation in terms of risk factors identified and eliminated. Implications for use of training and tools in participatory ergonomics approaches are discussed.

Relevance to industry

This study supports that ergonomics training should be a requisite for any participatory ergonomics approach. Given a fundamental level of ergonomics training, subjects demonstrated that they were better capable of identifying and eliminating risk factors in the job.     

The effects of a back belt on posture, strength, and spinal compressive force during static lift exertions

The experiment reported in this paper evaluated changes in lifting posture, static lifting strength and the estimated L3/L4 spinal compressive force resulting from the use of an abdominal support or ‘back' belt. Torso posture and maximum static lift strength were measured for eight male and eight female subjects using symmetric and asymmetric hand positions at calf height and elbow height. Body posture, and hand forces were also used as input to a three-dimensional static biomechanical model of the torso used to estimate L3/L4 spinal compressive force. The results showed axial twist of the torso to be significantly lower for calf height asymmetric exertions when the abdominal support belt was worn. The measured reduction in axial twist was approximately four degrees. No other significant effects on posture due to the support belt were found. Static lift strength was not significantly increased or reduced when the support belt was used. Predicted spinal compressive force was significantly lower when a support belt was worn (2840 N compared to 3125 N when the belt was not worn). Overall, the results of the experiment demonstrate a very limited benefit to the user of abdominal support belts, primarily due to reduced or restricted motion during asymmetric and lower-level lifts.Relevance to industryBack belts are commonly used in industry to mitigate manual materials handling hazards. One assumption often made by those recommending the use of back belts is that they substantially reduce the bending and twisting of the torso. The experiment reported in this paper tests this assumption and provides information on the utility of back belts.     

The effects of ergonomic interventions on low back moments are attenuated by changes in lifting behaviour

This study investigated the effects of ergonomic interventions involving a reduction of the mass (from 16 to 11 and 6 kg) and an increase in the initial lifting height (from pallet height to 90 cm above the ground) of building blocks in a mock-up of an industrial depalletizing task, investigating lifting behaviour as well as low back moments (calculated using a 3-D linked segment model). Nine experienced construction workers participated in the experiment, in which they removed building blocks from a pallet in the way they normally did during their work. Most of the changes in lifting behaviour that were found would attenuate the effect of the investigated interventions on low back moments. When block mass was reduced from 16 to 6 kg, subjects chose to lift the building block from a 10 (SD 10) cm greater distance from the front edge of the pallet and with a 100 (SD 66) degrees/s(2) higher trunk angular acceleration. When initial lifting height was increased, subjects chose to shift the building blocks less before actually lifting them, resulting in a 10.7 (SD 10) cm increase in horizontal distance of the building blocks relative to the body at the instant of peak net total moment. Despite these changes in lifting behaviour, the investigated ergonomic interventions still reduced the net total low back moment (by 4.9 (SD 2.0) Nm/kg when block mass was reduced and 53.6 (SD 41.0) Nm when initial lifting height was increased).