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PubMed2005

Natural breath control during lifting tasks: effect of load.

Anecdotal evidence suggests that people hold their breath during lifting tasks in order to increase intra-abdominal pressure (IAP) and thereby increase lumbar stability. Studies have shown that voluntary control of the breath influences IAP and that increases in IAP are related to increases in lumbar stability. However, a description of naturally occurring breath control during whole-body lifting tasks in normal healthy subjects is currently not available. Therefore, the specific aims of this study were to: (1) determine the naturally occurring breath patterns during lifting tasks in healthy subjects; (2) determine the effects of different levels of load during lifting tasks on natural breath control patterns in healthy subjects. The present study enrolled 20 healthy subjects to describe inspired volume and categories of airflow direction (inspiration, expiration, or breath hold) during two self-paced lifts of crates loaded at 5, 15, and 25% of body weight. When the breath pattern was examined across all loads there was a significant increase in the magnitude of inspired volume and the frequency of occurrence of inspiration immediately prior to lift-off. When examining the effect of load on breath patterns, there was a significant increase of inspired volume and occurrence of breath holding when lifting the heavy load compared to the medium and light loads. These results suggest that: (1) distinct patterns of natural breath control occur during lifting tasks; and (2) breath control is responsive to the timing and magnitude of load lifted.

Breathing Exercises↗
PubMed1999

Is there a rational basis for post-surgical lifting restrictions? 1. Current understanding.

Lifting restrictions postoperatively are quite common, but there appears to be little scientific basis for them. Lifting restrictions are inhibitory in terms of return to work and may be a factor in chronicity. The mean functional spinal motion unit stiffness changes with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting restrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accommodations such as lifting aids. Such restrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition.

Diskectomy↗
PubMed1999

Is there a rational basis for post-surgical lifting restrictions? 2. Possible scientific approach.

Lifting restrictions postoperatively are quite common but there appears to be little scientific basis for them. Lifting restricitions are inhibitory in terms of return to work and may be a factor in chronicity. The mean changes in functional spinal motion unit (FSU) stiffness with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting resctrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accomodations such as lifting aids. Such resitrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition.

Diskectomy↗
PubMed2004

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.

Adult↗
PubMed2005

Evaluation of the effectiveness of portable ceiling lifts in a new long-term care facility.

Researchers and health and safety practitioners have advocated replacing manual patient handling techniques with ceiling lifts in long-term care. The majority of these studies have only evaluated the impact of fixed ceiling lifts on extended care residents where the ratio of ceiling lifts to resident beds is one to one. This pre-post intervention study assesses the effectiveness of portable ceiling lifts in a new multi-level care facility on risk of patient handling injuries where the ratio of ceiling lifts to resident beds is one to six. Results indicated that staff perceived they were at significantly (p<0.05) less risk of injury when using ceiling lifts compared to manual methods. Seventy-five percent of staff preferred to use the ceiling lifts over any other method for lifting and transferring residents. Compensation costs due to patient handling decreased in the intervention facility, with a 241% increase in the comparison facility. This study demonstrates that incorporating ceiling lifts into the design of a new multi-level care facility reduced patient handling injuries and decreased perceived risk of injury among care staff.

Adult↗
PubMed2006

The effects of work experience, lift frequency and exposure duration on low back muscle oxygenation.

BACKGROUND: Previous studies have shown changes in low back muscle oxygenation after static muscle contractions or short-term dynamic lifting exertions. The aim of this study was to document the changes in low back muscle oxygenation during prolonged lifting activity over an entire workday as of function of work experience and lift frequency. METHODS: Four novice and six experienced subjects participated in a lifting study in which they lifted load with a given weight at one of five different frequencies (2, 4, 8, 10, 12 lifts/min) for an 8-h period. Oxygen saturation of the left and right erector spinae was measured continuously and non-invasively using near-infrared spectroscopy during each lifting session. FINDINGS: Exposure duration had a statistically significant effect on muscle oxygenation level (P<0.0001). Oxygen saturation in the erector spinae increased during the 8-h lifting period. As lift frequency increased, back muscle oxygenation in experienced subjects also increased. In general, the increase in muscle oxygenation for experienced subjects was less than that for novice subjects. INTERPRETATION: This study suggested that the requirement of oxygen for the low back muscle in a typical industrial lifting job increased over time and experienced workers responded differently from the novice subjects. These findings may provide more insight into the physiological changes of the working muscle and the potential risks of developing muscle injury.

Back↗
PubMed1999

Variation in spinal load and trunk dynamics during repeated lifting exertions.

OBJECTIVES: To quantify the variability in lifting motions, trunk moments, and spinal loads associated with repeated lifting exertions and to identify workplace factors that influence the biomechanical variability. DESIGN: Measurement of trunk dynamics, moments and muscle activities were used as inputs into EMG assisted model of spinal loading. BACKGROUND: Traditional biomechanical models assume repeated performance of a lifting task produces little variability in spinal load because the assessments overlook variability in lifting dynamics and muscle coactivity. METHODS: Five experienced and seven inexperienced manual materials handlers performed 10 repeated lifts at each combination of load weight, task asymmetry and lifting velocity. RESULTS: Box weight, task asymmetry and job experience influenced the magnitude and variability of spinal load during repeated lifting exertions. Surprisingly, experienced subjects demonstrated significantly greater spinal loads and within-subject variability in spinal load than inexperienced subjects. Trial-to-trial variability accounted for 14% of the total variation in compression overall and 32% in lateral shear load. Although the mean spinal load was safely below the NIOSH recommended limit; due to variability about the mean, more than 20% of the lifts exceeded the recommended limit. CONCLUSION: Spinal load changed markedly from one exertion to the next despite identical task requirements. Trial-to-trial variability in kinematics, kinetics, and spinal load were influenced by workplace factors, and may play a role in the risk of low-back pain. RELEVANCE: Ergonomic assessments considering only the mean value of spinal load overlook the fact that a large fraction of the lifts may exceed recommended levels.

Adult↗
PubMedDate not supplied

Gender influences on spine loads during complex lifting.

BACKGROUND CONTEXT: Previous research has documented differences in spine loading between genders when the imposed load is normalized relative to the size of the person. However, under realistic work conditions the magnitude of the load handled is seldom adjusted relative to worker anthropometry. Thus, there is a void in our knowledge in that we do not understand how material handling influences spine loading and potential risk of injury as a function of gender under realistic lifting situations. PURPOSE: To evaluate the differences in spine loading between men and women when exposed to similar workplace demands. STUDY DESIGN: A laboratory study was conducted to investigate the biomechanical responses during realistic free-dynamic lifting tasks when subjects lifted from origins and destinations that were either fixed or set relative to the subject's anthropometry. PATIENT SAMPLE: Twenty men and 20 women asymptomatic for low back pain were recruited to participate in the study. OUTCOME MEASURES: The three-dimensional spine loads were predicted from a well-established electromyography-assisted model. METHODS: Both genders completed a series of symmetric and asymmetric (60-degree clockwise) lifts that originated from two shelf heights ("relative" to knee height and "set" at 35 cm from floor) and terminated at one of two destination heights ("relative" to waist and "set" 102 cm from the floor). Three levels of box weight were investigated (6.8, 13.6 and 22.7 kg). RESULTS: Men had significantly greater compression forces than women (about 640 N). Loading differences between genders were further magnified by several of the workplace factors. The differences between men and women were even greater when lifting either of the heavier loads from the lower fixed shelf (more than 50% greater). CONCLUSIONS: It is apparent that men produce the greater loads on their spines during lifting. However, engineering controls, such as adjustable workplace layout or less weight lifted, may reduce or eliminate gender-specific differences in spine loads. Furthermore, the differences in spine loads appear to be a result of kinematic trade-offs and muscle coactivity differences in combination with unequal body masses between genders. However, when the loads were put into context of the expected tolerances of the spine, women were found to be at increased risk of injury, especially when lifting heavy loads or under asymmetric lifting conditions. Collectively, the results indicate the need to account for differences between the genders when designing the workplace.

Adult↗
PubMed2003

What is a demanding lifting job for manual handling workers in Hong Kong?

Although lifting tasks are traditionally evaluated by researchers, through the use of methods which depend on one or more approaches (i.e., psychophysical, biomechanical and physiological methods), none of these approaches makes use of expert workers in the evaluation of lifting activities. Given that 97% of lower back symptoms are aches, pains and discomfort and rely on self-reports, it is intuitive to use expert workers in evaluating the stressfulness of lifting activities. In this investigation, 217 workers from three industries in the Hong Kong area were surveyed to determine what constitutes a demanding lifting job from a worker standpoint. This was achieved by asking workers to map, in numerical terms, the level of lifting task parameter described in linguistic values. For example, the weight of load was described in three linguistic descriptors, namely, 'light', 'moderate' and 'heavy'. Then, each worker was asked to assess the meaning of these linguistic descriptors in numerical terms, based on their perception and experience with manual handling work. In this study, workers were asked to map the physical analogue of linguistic descriptors for seven lifting task parameters which are utilized in the NIOSH lifting equation, that is, weight of load, horizontal distance, vertical travel distance, vertical origin of lift, angle of asymmetry, frequency of handling and task duration. The data obtained from the workers were then subjected to validity testing in relation to norms and values reported in the published literature. On a preliminary basis, it appears that workers' assessments are logical and valid. The results suggest that the worker-based methodology is a promising approach and that it is worthwhile to pursue this approach further in the evaluation of industrial lifting activities.

Adult↗
PubMed1995

Development of factor-score-based models to explain and predict maximal box-lifting performance.

The objectives of the study were threefold: (1) to develop factor-score-based models to predict maximum mass on a box-lifting task using multiple regressions; (2) to compare predictive and explanatory powers of factor-score-based models to models derived from data-level variables; and (3) to apply these findings to ergonomic research and practical problem-solving situations. Forty-eight volunteers (25 women and 23 men) completed a maximal box-lifting task and a maximal isoinertial lifting test on an Incremental Lifting Machine (ILM). Dynamic data collected during isoinertial testing were summarized into 32 lift parameters, and then subjected to principal components analyses using the 'FACTOR PROCEDURE' from the Statistical Analysis System (SAS). Factor scores were calculated for each participant on each of the four factors comprising the final solution, and multiple regression equations for men, women and combined data were generated using the 'GENERAL LINEAR MODELS' procedure from SAS. Results revealed that prediction of box-lifting performance was optimized when regression equations were developed using numerous data-level variables as predictors, i.e., all 32 lift parameters and ILM mass. In comparison, explanation was enhanced but predictive capabilities were reduced when linear models were formed using ILM mass and the factor scores derived from analyses of isoinertial lifting. The use of variables loading on the factors gave slightly increased predictive power than did the factor-score-based models. Similar trends in predictive and explanatory powers appeared when the data were analysed according to gender. Ergonomic applications of factor-score-based models were discussed with regard to ongoing research as well as to practical problem-solving situations. It was concluded that the advantages and usefulness of factor-score-based models warranted their inclusion in future investigations of lifting performance.

Adult↗
PubMed1998

Evaluation of the ability of power to predict low frequency lifting capacity.

An experiment was conducted to examine the role that maximal lifting power has in predicting maximum acceptable weight of lift (MAWL) for a frequency of one lift per 8 h. The secondary aim of the study was to compare the ability of power to predict MAWL to previously used measures of capacity including two measures of isometric strength, five measures of isokinetic strength, and isoinertial capacity on an incremental lifting test. Twenty-five male subjects volunteered to participate in the experiment. The isometric tests involved maximum voluntary contractions for composite lifting strength at vertical heights of 15 and 75 cm. Peak isokinetic strength was measured at velocities of 0.1, 0.2, 0.4, 0.6 and 0.8 m s-1 using a modified CYBEX II isokinetic dynamometer. Isoinertial lifting capacity was measured on the X-factor incremental lifting machine and peak power was measured on the incremental lifting machine by having subjects lift a 25 kg load as quickly as possible. The results indicate that peak isoinertial power is significantly correlated with MAWL, and this correlation was higher than any of the correlations between the other predictor variables and MAWL. The relationships between the isokinetic strength measures and MAWL were stronger than the relationships between the isometric measures and MAWL. Overall, the results suggest that tests used to predict MAWL should be dynamic rather than static.

Adult↗
PubMed1999

Beyond psychophysics: the need for a cognitive engineering approach to setting limits in manual lifting tasks.

The classical psychophysical approach to setting limits in manual lifting tasks is discussed in view of experimental procedures used, non-linearity of human perception of load heaviness, and the related experimental outcomes. The results of two studies investigating the human assessment of load acceptability and safety are presented. The first study compares the classical concept of the maximum acceptable weight of lift (MAWL) to the alternative concept of the maximum safe weight of lift (MSWL). The second study utilizes the linguistic magnitude estimation (LME) method to mathematically model human assessment of four categories of lifted loads, including the concepts of acceptable, safe, not-too-heavy, and too-heavy loads for continuous lifting. It is shown that the concepts of the lifted load acceptability and safety are non-linear, and can be modelled with great accuracy using the third degree polynomials. This study also introduces and investigates the concept of the load indifference in assessment of load heaviness, and shows that lack of a cognitive benchmark introduces inconsistency in subjects' perception of load acceptability and safety compared to the concept of too-heavy load for continuous lifting. It is concluded that a new research approach to manual lifting tasks based on cognitive engineering is needed to improve the quality of research methodologies currently utilized in this field. This unexplored area of research should lead to greater understanding of human capacities and limitations in manual lifting tasks in the context of cultural and linguistic anthropology.

Adult↗
PubMed1987

Electromyographic analysis of two techniques for squat lifting.

The purpose of this study was to examine the effects of two different alignments of the lumbar spine and three different loads on electromyographic activity of the erector spinae (ES) and oblique abdominal (OA) muscles during squat lifting. Nineteen healthy subjects (8 men, 11 women) participated in this study. Each subject performed squat lifts both with the lumbar spine aligned in "back-bowed-in" (BBI), or normal, lordosis and with the lumbar spine aligned in "back-bowed-out" (BBO), or relatively less, lordosis. Based on total duration, the lift was divided into two equal phases. Electromyographic activity of each muscle was quantified for each half of the lift and normalized to the total EMG produced by the muscle during a maximal voluntary isometric contraction. A three-way analysis of variance for repeated measures was used to analyze the effects of position of the lumbar spine, timing, and load on the amount of EMG activity during lifting. For all loads, ES muscle activity was greater during the first half of the BBI lift, whereas OA muscle activity was greater during the first half of the lift, regardless of the lifting style (p less than .01). The greater ES and OA muscle activity occurring during the crucial initial period in the BBI lift may provide the best protection for the lumbar spine.

Abdominal Muscles↗
PubMed2003

Weight lifted in strength training predicts bone change in postmenopausal women.

PURPOSE: The aim of this study was to examine the relationship between weight lifted in 1 yr of progressive strength training and change in bone mineral density (BMD) in a group of calcium-replete, postmenopausal women. METHODS: As part of a large clinical trial, 140 calcium-supplemented women, 44-66 yr old, were randomized to a 1-yr progressive strength-training program. Half of the women were using hormone replacement therapy. Three times weekly, subjects completed two sets of six to eight repetitions in eight core exercises at 70-80% of one repetition maximum. BMD was measured at baseline and 1 yr. RESULTS: In multiple linear regression, the increase in femur trochanter (FT) BMD was positively related to total weight lifted (0.001 g.cm (-2)) for a SD of weight lifted, P< 0.01) after adjusting for age, baseline factors, HRT status, weight change, cohort, and fitness center. The weighted squats showed the strongest (0.002 g.cm(-2)) for a SD of weight lifted, P< 0.001), whereas the back extension exhibited the weakest (0.0005 g.cm(-2)) for a SD of weight lifted, P< 0.26) association with change in FT BMD. The amount of weight lifted in the weighted march exercise was significantly related to total body BMD (0.0006 g.cm(-2)) for a SD of weight lifted, P< 0.01). The associations between weight lifted and BMD for the femur neck or lumbar spine were not significant. CONCLUSION: Evidence of a linear relationship between BMD change and total and exercise-specific weight lifted in a 1-yr strength-training program reinforces the positive association between this type of exercise and BMD in postmenopausal women.

Absorptiometry, Photon↗
PubMed1998

An assessment of complex spinal loads during dynamic lifting tasks.

STUDY DESIGN: An electromyogram-assisted free-dynamic lifting model was used to quantify the patterns of complex spinal loads in subjects performing various lifting tasks. OBJECTIVES: To assess in vivo the three-dimensional complex spinal loading patterns associated with high and low risk lifting conditions that matched those observed in industrial settings. SUMMARY OF BACKGROUND DATA: Combined loading on the spine has been implicated as a major risk factor in occupational low back disorders. However, there is a void in the literature regarding the role of these simultaneously occurring complex spinal loads during manual lifting. METHODS: Eleven male subjects performed symmetric and asymmetric lifting tasks with varying speed and weight. Reactive forces and moments at L5-S1 were determined through the use of electrogoniometers and a force plate. An electromyogram-assisted model provided the continuous patterns of three-dimensional spinal loads under these complex lifting tasks. RESULTS: The results showed that complex dynamic motions similar to those observed in risky industrial tasks generated substantial levels of combined compressive and shear loads. In addition, higher loading rates were observed under these conditions. Unlike loading magnitudes, loading rate was a better indicator of dynamic loading because it incorporated both the duration and magnitude of net muscle forces contributing to total spinal loading during the lifting conditions. CONCLUSIONS: Quantification of spinal combined motions and loading in vivo has not been undertaken. This study provided a unified assessment of the effects of combined or coupled motions and moments in the internal loading of the spine. Dynamic lifting conditions similar to those observed in risky industrial situations generated unique complex patterns of spinal loading, which have been implicated to pose a higher risk to the spinal structure. The higher predicted loading and loading rate during asymmetric lifting conditions can be avoided by appropriate ergonomic workplace modifications.

Adult↗
PubMed1999

Effect of lifting belts on trunk muscle activation during a suddenly applied load.

The National Institute for Occupational Safety and Health suggests there is insufficient biomechanical or epidemiological evidence to recommend the use of back belts in industry. From a biomechanical perspective, previous work suggests that lifting belts stiffen the torso, particularly in the frontal and transverse planes. To determine whether lifting belts stiffen the torso and alter the trunk muscle response during a sudden loading event, we tested the hypotheses that (a) lifting belts alter peak muscle activity recorded with electromyography (EMG) during sudden loading and (b) lifting belts have a larger impact on trunk muscle response when sudden loads are applied asymmetric to the torso's midsagittal plane. A sudden load was delivered to 10 men and 10 women without history of low back disorder via a cable attached to a thoracic harness; motion was restricted to the lumbar spine. Results indicate that gender was not a significant factor in this study. The lifting belt reduced the peak normalized EMG of the erector spinae muscles on average by 3% during asymmetric loading, though peak normalized EMG was increased by 2% during symmetric loading. Lifting belts have been shown to slightly reduce peak erector spinae activity during asymmetric sudden loading events in a constrained paradigm; however, the effects of lifting belts are too small to provide effective protection of workers. Actual or potential applications include the assessment of lifting belts as protective devices in workers based on the effects of lifting belts on the trunk muscle activity.

Adult↗
PubMed1989

Effects of a belt on intra-abdominal pressure during weight lifting.

Intra-abdominal pressure (IAP) has been widely hypothesized to reduce potentially injurious compressive forces on spinal discs during lifting. To investigate the effects of a standard lifting belt on IAP and lifting mechanics, IAP and vertical ground reaction force (GRF) were monitored by computer using a catheter transducer and force platform while nine subjects aged 28.2 +/- 6.6 yr dead-lifted a barbell both with and without a lifting belt at 90% of maximum. Both IAP and GRF rose sharply from the time force was first exerted on the bar until shortly after it left the floor, after which GRF usually plateaued while IAP either plateaued or declined. IAP rose significantly (P less than 0.05) earlier with than without the belt. When the belt was worn, IAP rose significantly earlier than did GRF. Both with and without the belt, IAP ended its initial surge significantly earlier than did GRF. Variables significantly greater with than without a belt included peak IAP, area under the IAP vs time curve from start of initial IAP surge to lift-off, peak rate of IAP increase after the end of its initial surge, and average IAP from lift-off to life completion. In contrast, average rate of IAP increase during its initial surge was significantly lower with the belt. Correlations are presented which provide additional information about relationships among the variables. Results suggest that the use of a lifting belt increases IAP, which may reduce disc compressive force and improve lifting safety.

Abdomen↗
PubMedDate not supplied

Tolerability to prolonged lifting tasks. A validation of the recommended limits.

Prolonged physical exertion is subjectively regulated by the perception of effort. This preliminary study was conducted to validate the use of subjective perceptions of effort in assessing objectively tolerable workloads for prolonged lifting tasks. Ten healthy male subjects tested their maximal lifting capacity (MLC) on a lift dynamometer (LidoLift, Loredan Biomed., West Sacramento, CA) and underwent incremental and 30-minute endurance lifting tests. Cardiorespiratory parameters were monitored with an oxygen uptake analyzer, mechanical parameters were calculated using a computerized dynamometer. Ratings of perceived exertion were given on Borg's 10-point scale. Physiological responses to repetitive lifting were matched with subjective perceptions. A single-variable statistical regression for power functions was performed to obtain the individual "iso-perception" curves as functions of the mechanical work exerted. We found that the "iso-perception" curve corresponding to a "moderate" perception of effort may represent the individual "tolerance threshold" for prolonged lifting tasks, since physiological responses at this level of intensity did not change significantly and the respiratory exchange ratio was less than one. The individually tolerable weight for lifting tasks lasting 30 min has been expressed as a percentage of the isoinertial MLC value and compared with the currently recommended limits for prolonged lifting tasks (Italian legislation D.L. 626/94). On the basis of our preliminary results a "tolerance threshold" of 20% MLC has been proposed for prolonged lifting tasks.

Adult↗