Lowering Tasks Research Articles

Pulling force in lateral lifting and lowering

This work investigated maximal voluntary lateral hand pulling force in 18 healthy, habitually active men. Measurements were made in standing at different static angles of lateral trunk flexion, as well as at different constant lifting and lowering velocities. Movement was constrained to the frontal plane, velocity was controlled by an isokinetic dynamometer, pulling force was measured with a strain gauge and overall lateral angular displacement of the trunk by an electrogoniometer. Mean peak pulling force values ranged from 478 to 658 N (static), 291 to 528 N (lifting), and 801 to 911 N (lowering), respectively. The static pulling forces were the highest in flexed positions to the loaded side (10 and 20 trunk angles). In lifting, peak and position-specific pulling force decreased with increasing velocity. Peak lifting force occurred in a flexed trunk position of 7 to 9 to the loaded side. In lowering, pulling forces were significantly higher than during lifting at corresponding velocities and showed less changes with velocity. Peak lowering force occurred at a trunk angle of- 7 to- 11, that is towards the unloaded side. In conclusion, maximal voluntary pulling force in the frontal plane was found to be task dependent. Lowering was accompanied by higher forces and a different velocity and position dependency than lifting which, in addition to the fact that the trunk muscles act predominantly eccentrically during the lowering task, may impose an increased risk of injury.

Evaluation of spinal loading during lowering and lifting

Objective. To estimate the three-dimensional spinal loads during various lifting and lowering tasks. Design. The in vivo measurements of the trunk dynamics, moments, and myoelectric activity were used as inputs into an electromyographic-assisted model used to predict the three-dimensional spinal loads. Background. Previous studies of eccentric motions have investigated muscle activity, trunk strength, and trunk moments. A void in the body of knowledge exists in that none of these studies investigated spinal loading. Methods. Ten subjects lifted (40 ° of flexion to 0 °) and lowered (0 ° of flexion to 40 °) boxes while positioned in a structure that restrained the pelvis and hips. The tasks were performed under isokinetic trunk velocities of 5, 10, 20, 40, and 80 deg s −1 while holding a box with weights of 9.1, 18.2, and 27.3 kg. Results. Lowering strength was found to be 56% greater than lifting strength. The lowering tasks produced significantly higher compression forces but lower anterior-posterior shear forces than the lifting tasks. The differences in the spinal loads produced by the two lifting tasks were attributed to differences in coactivity and unequal lifting moments (i.e. holding the box farther away from the body). Conclusions. The nature of the spinal loads that occur during lowering and lifting were significantly different. The difference in spinal loads may be explained by different lifting styles.

The effect of complex dynamic lifting and lowering characteristics on trunk muscles recruitment

A better understanding of how the neuromuscular spinal system behaves during lifting and lowering could provide more insight about potential causes of occupational low back disorders (LBDs), and could help in the prevention and rehabilitation process of these disorders. The purpose of this study was to quantify trunk muscle activities under various whole-body free-dynamic symmetric and asymmetric complex lifting and lowering tasks. Eleven male subjects with no prior history of LBDs participated in the study. Electromyographic activities of ten trunk muscles were monitored while subjects either symmetrically or asymmetrically lifted and lowered a box under three different speeds and three weights. The results showed that all ten muscles were responsive to various experimental conditions with the erector spinae and internal oblique muscles showing the greatest response. Substantial electromyographic activities were observed in muscles that were on the contralateral side of the load. Lowering conditions yielded consistently lower muscular activities than their corresponding lifting conditions. These results show that it is essential to consider multiple trunk muscles in modeling efforts of quantifying spinal loading, as well as for back rehabilitation research purposes.

Maximum acceptable weight of asymmetrical lifting and lowering of postal sacks

The asymmetrical lifting of postal sacks without handles was simulated. Type-2 and Type-3 postal sacks (those typically used by the U.S. Postal Service) were loaded and unloaded from and to different cart and conveyor levels. An adjustable table was used to simulate the different conveyor levels. There were six combinations of lift for each of twenty participants (ten male and ten female). A modified version of the psychophysical methodology was used to determine the maximum acceptable weight of lift. A significant difference was found between the weights lifted across cart heights. Specifically, the mean load lifted over the 96.5 cm (38.0 in) cart height was 15.337 kg (33.74 lb) and was significantly greater than the average load lifted across the 20.40 cm (8.0 in) and the 104.20 cm (41.0 in cart heights. However, this difference is not practically significant different (mean difference = 1.44 kg). There was no significant difference ( p > 0.05). This lifted across table heights. A significant interaction occurred between cart height and conveyor height ( p < 0.05). This interaction indicated that as the vertical distance between the cart height and the conveyor height increased, the acceptable load handling capabilities of the participants decreased. The mean MAWL for Type-2 postal sacks (14.5 kg, 31.91 lb) was similar to the mean weight lifted at the postal distribution center (16.4 kg, 36.0 lg). The mean MAWL for Type-3 sacks (14.5 kg, 31.9 lbs) was less than half of the mean weight lifted at the postal distribution center (24.6 kg, 54.1 lb). The results of this study have direct implication regarding the design of postal operations, the types of lifting and lowering tasks that should and should not be performed, as well as more practical weight limitations than are previously employed in these types of operations.

The Effect of Lifting vs. Lowering on Spinal Loading

In industry, workers perform tasks requiring both lifting and lowering. During concentric lifting, the muscles are shortening as the force is being generated. Conversely, the muscle lengthens while generating force during eccentric lowering. While research on various lifting tasks is extensive, there has been limited research performed to evaluate the lowering tasks. Most of the research that does exist on lowering has investigated muscle activity and trunk strength. None of these studies have investigated spinal loading. The current study estimated the effects of lifting and lowering on spinal loads and predicted moments imposed on the spine. Ten subjects performed both eccentric and concentric lifts under sagittally symmetric conditions. The tasks were performed under isokinetic trunk velocities of 5, 10, 20, 40, and 80 deg/s while holding a box with weights of 9.1, 18.2, and 27.3 kg. Spinal loads and predicted moments in three dimensional space were estimated by an EMG-assisted model which has been adjusted to incorporate the artifacts of eccentric lifting. Eccentric strength was found to be 56 percent greater than during concentric lifting. The lowering tasks produced significantly higher compression forces but lower anterior-posterior shear forces than the concentric lifting tasks. The differences in the spinal loads between the two lifting tasks were attributed to the internal muscle forces and unequal moments resulting from differences in the lifting path of the box. Thus, the differences between the lifting tasks resulted from different lifting styles associated with eccentric and concentric movements

Effects of body posture, weight and frequency on time-dependent muscle strengths during dynamic materials handling tasks

We examined the effects of body posture, weight and frequency on time-dependent muscle strengths during dynamic materials handling tasks. Maximum voluntary isometric strengths (MVIS) of nine healthy males were evaluated for symmetric and asymmetric postures, respectively, and their time-dependent muscle strengths were measured after performing 2 hours of lifting and lowering tasks with varying conditions. The percentage decrease in normalized MVIS after performing each task was then reported. The mean MVIS across the subjects for the asymmetric posture of 90° lateral plane to the right was significantly lower than that for the symmetric posture. The percentage decrease in MVIS after performing the asymmetric tasks was found to be significantly greater than that for the symmetric tasks. A correction factor of 34.1% is recommended to modify the sagittally symmetric MVIS data when they are utilized in the asymmetric posture of 90°. Furthermore, the MVIS data should be adjusted by 13.4% and 24.2% for durations of 2 hours for symmetric and asymmetric tasks, respectively.

Load Acceleration and Footstep Strategies in Asymmetrical Lifting and Lowering.

Accelerated execution effects for lifting and lowering a 12-kg box using two footstep strategies associated with experienced workers were studied. Eight healthy male participants performed a normal and an accelerated execution of a lifting task and a lowering task, using a minimal feet displacement strategy (oblique-step) and a strategy with a step (crossed-step). It was hypothesized that the accelerated executions, as compared to the normal executions, would have a different effect on L5/S1 resultant moment, body posture, and other kinematic variables. A tridimensional dynamic rigid body model was used to compute L5/S1 resultant moments. Results showed that the accelerated condition did not reduce body asymmetry of posture, but it reduced the length of the path of the global center of gravity and the duration of the supporting phase of the box, and it did not significantly affect L5/S1 maximal resultant moments for lifting but increased them for lowering. These results indicate that the net work production for accelerated strategies might be smaller, which may represent an economy of energy. Furthermore, the results showed that the use of an accelerated strategy for lowering should be avoided.

The effect of back belts on lumbar muscle fatigue.

An experiment was conducted to investigate the effect of wearing a weight lifting belt on the endurance and fatigue characteristics of the extensor muscles of the spine. To evaluate the effectiveness of back belts in preserving the endurance characteristics of the spinal musculature. Previous studies have investigated the use of back belts in increasing intra-abdominal pressure and thus increasing the stabilization of the spine. Other studies have looked at the association of low back disability and wearing back belts. No study has examined the relationship between wearing back belts and measures of spinal muscle fatigue and endurance. Thirteen male industrial workers performed a lifting and lowering task from the floor to a 76.2 cm height at 4.3 min-1 2 days a week for 4 weeks. The load was psychophysically determined and averaged 28.1 kg for a total of 28.9 metric tons moved in 4 hours. Subjects lifted for 1, 2, 3, and 4 hours, respectively, for the first 4 days of the experiment. These were considered training days. During the last 4 days, subjects lifted for 4 hours per day; 2 days with a back belt, and 2 days without a back belt. Maximum isokinetic endurance of the extensors was measured for 50 repetitions (5 sets of 10 repetitions) at the end of 4 hours of lifting. Median frequencies of the electromyographic signal from six locations over the back extensors were measured for 30 seconds at 80% of maximum isometric voluntary contraction after 4 hours of lifting. There were no significant differences in maximum isokinetic endurance, or in the slope of median frequency, between lifting with a back belt and lifting without a back belt. Similarly, a modified Borg scale and a postexperiment survey question were unable to distinguish between wearing a back belt and not wearing a back belt. There were no significant differences in maximum isokinetic endurance and electromyographic spectral parameters of the back extensor muscles as a result of wearing a back belt during heavy lifting and lowering tasks.

Physical Fatigue in High and Very High Frequency Manual Materials Handling: Perceived Exertion and Physiological Indicators

This paper presents the results of a preliminary laboratory study undertaken to determine the perceived exertion and physiological responses of highly trained and experienced workers to high (up to 16 repetitions/min) and very high frequency (above 16 repetitions/min) manual lifting, lowering, and carrying/turning tasks. The results indicate that workers engaged in such highly repetitive and physically demanding tasks may operate at psychophysical workloads that may clearly be considered physically fatiguing and unacceptable according to the current physiological design criteria. In this study subjects performing lifting and lowering tasks, on the average, operated at 57% and 52% of their uphill treadmill aerobic capacity, respectively. For carrying and turning tasks, the average metabolic energy expenditure rate corresponded to 43% of subjects' aerobic capacity. The overall heart rates of the study subjects were 155 beats per minute (bpm) for lifting, 144 bpm for lowering, and 142 bpm for carrying and turning. These physiological responses, when compared with recommended physiological design criteria, are excessively high. The ratings of perceived exertion (RPE) for the shoulder, back, and whole body were highest for lifting (range, 10.20-15.50) and least for carrying and turning (range, 10.30-13.40; carrying and turning activities also included RPE of arms). Generally workers perceived the associated physical exertions as acceptable.

Joint moments and muscle activity in the lower extremities and lower back in lifting and lowering tasks

The mechanical loading on the body during the act of lifting has been estimated frequently. The opposite act of lowering has received much less attention. The aim of the present study was to compare the mechanical loading of the musculoskeletal system in lifting and lowering. Eight subjects repetitively lifted and lowered a load, using two different techniques (a leg and a back technique). The ankle, knee, hip and lumboscral joint moments were estimated and the myoelectrical (EMG) activity of seven (leg and back) muscles was recorded. The differences between the lifting and lowering phase for the leg technique were similar to those observed when the back technique was applied. The joint moment curves in lifting showed a high level of agreement with the (time-reversed) moment curves in lowering. Peak moments in lowering were only slightly lower than in lifting (peak lumbar moments were 5.4% lower). These small differences were related to different acceleration profiles at the centre of gravity of the body/load complex. The EMG activity was considerably lower in lowering than in lifting. The mean EMG in lowering (average for seven muscles) was only about 69% of the EMG in lifting. This was attributed to the different types of muscle actions involved in lifting (mainly concentric) and lowering (mainly eccentric). Furthermore, the EMG results suggest that similar inter-muscular coordination is involved in lowering and lifting. The results give rise to the assumption that in lifting and lowering similar muscle forces are produced to meet the (nearly) equal joint moments, but in lowering these forces are distributed over a smaller cross-sectional area of active muscle, which might imply a higher risk of injury.

A psychophysiological study of high and very high frequency manual materials handling: Part I - Lifting and lowering

This paper describes the first part of a two-part study undertaken to determine the psychophysical and physiological responses of male workers to short duration (2 hours), high (up to 16 times per minute) and very high (above 16 times per minute) frequency manual handling tasks. Manual lifting and lowering tasks were studied in the first part of the study. The handling frequencies investigated were: 14, 16, 18, 20, and 22 per minute. Ten highly trained males participated in the study. Their metabolic energy expenditure rate, heart rate, and ratings of perceived exertion (RPE) of the shoulders, back, and whole body at the maximum acceptable weight of lift/lower were determined. How the physiological responses changed with the working duration was also investigated. The results indicated that heart rate and oxygen uptake remained steady with the working duration. Although the maximum acceptable weight declined significantly with frequency, the sample population chose a consistent work rate (approximately 145 kg-m/min, on the average). Other responses, however, were not affected significantly by frequency. Also, on the average, subjects performing manual lifting tasks operated at approximately 60% of their lifting aerobic capacity (equivalent to approximately 57% of their graded treadmill aerobic capacity). Subjects performing lowering tasks operated at 55% of their lifting aerobic capacity, on the average (equivalent to approximately 52% of their graded treadmill aerobic capacity). These findings are substantially different from those observed in previous studies for 8-hour work shifts and lower frequencies and indicate that individuals performing high and very high frequency manual lifting or lowering tasks are subjected to very high physical and physiological burden.

The influence of dynamic factors on triaxial net muscular moments at the [formula omitted] joint during asymmetrical lifting and lowering

Asymmetrical lifting and lowering are predominant activities in the workplace. Mechanical causes are suggested for many back injuries and the dynamic conditions within which spine loading occurs are related to spine loading increase. More data on tridimensional biomechanical lumbar spine loading during asymmetrical lifting and lowering are needed. A tridimensional dynamic multisegment model was developed to compute spinal loading for asymmetrical box-handling situations. The tridimensional positions of the anatomical markers were generated by a direct linear transformation algorithm adapted for the processing of data from two real and two virtual views (mirrors). Two force platforms measured the external forces. Five male subjects performed three variations (slow, fast and accelerated) of asymmetric lifting and two variations (slow and fast) of asymmetric lowering. The torsional, extension/flexion and lateral bending net muscular moments at the L5 S1 joint were computed and peak values selected for statistical analysis. For the lifting task, the fast and accelerated conditions showed significant increases over the slow condition for torsion, extension/flexion and lateral-bending moments. The accelerated condition also showed significant increases over the fast condition for extension. A comparison between lifting and lowering tasks showed equivalent loadings for torsion and extension. The moments were compared to average maximal values measured on equivalent male subject populations by isokinetic dynamometry. This showed torsional and extension values of 30 and 83% of the maximal possible subject capacity, respectively. These results demonstrated that dynamic factors do influence the load on the spine and highlighted the influence of both lifting and lowering on the loading of the spine. This suggested that for a more complete analysis of asymmetrical handling, the maximal velocity and acceleration produced during lifting should be included.

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age = 36.9 yrs +/- 4.5 SD) participated in a study examining psychophysically acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted head-room conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60 cm). All tasks were 10 min in duration and were performed under a 1.22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11.3% lower when kneeling as compared to stooping. Subjects selected 3.5% more weight in asymmetric tasks, and lifted 5.0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3.5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8.2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.

Muscular mechanical energy expenditure as a process for detecting potential risks in manual materials handling

The problem of injuries in manual materials handling remains a big concern in industrialized countries. It has become imperative in occupational biomechanics to extend the analyses to all pertinent factors involved in working tasks and to adopt an experimental approach leading to the understanding of the relative demands imposed simultaneously on all body joints. The evaluation of joint muscular work and the processes of energy generation, absorption and transfer appears promising as a tool in the detection of risk factors in working tasks. The present study consisted of evaluating two tasks (lifting and lowering) performed at five different heights (from 15 to 185 cm) with five different loads (from 3.3 to 22.0 kg). The subjects were eight experienced workers from a food product warehouse. Cinematography techniques and two AMTI force platforms were used to collect the data. Dynamic and planar segmental analyses were performed to calculate the net muscular moments at the joints, and work was calculated from the integration of muscular power. Factorial analyses of variance with repeated measures were performed on the dependent variables to evaluate the main effects of tasks, loads, and heights (for lifting and for lowering) and the interactions. The results revealed the adoption of different movement strategies in the handling of heavier loads. In the first, a larger emphasis of energy transfer and movement economy; in the second, a reduction in the relative contribution of the shoulders to the detriment of an increased participation of the lower back and hips was found. The comparison between lifting and lowering tasks indicated that lifting was only slightly more demanding than lowering for maximum muscular moments (about 15%) but much more so for mechanical work (about 40%); however, the nature of the efforts in eccentric contractions suggests that the lowering of heavy loads may be risky. Finally, the results revealed the deviation of height of handling from the waist level to be a significant factor. Handling at lower heights was considerably more demanding but the work was shared by several joints, mainly by the hips and lower back (about 70%); on the other hand, in handling above the waist, the work efforts were concentrated on the upper limbs (about 80%). In most cases, the participation of lower limbs was minimal and some movement strategies are suggested for future research.

The effects of the reach and level of lifting/lowering tasks on metabolic cost in symmetric and asymmetric planes

The energy consumption in the workspace envelope around operators was studied for lifting and lowering tasks. The entire working space was bisected into two identical halves. Within one, 81 target locations were selected. Six male young adults (mean age 27.3 years and mean weight 73.8 kg) stoop lifted and lowered 2.5, 5.0, and 10.0 kg loads from floor to their respective knee, hip, and shoulder heights in mid-sagittal, 30° lateral, and 60° lateral planes at half, three-quarters, and full reach distances. The steady state oxygen uptake was measured for quiet standing and the 81 activities. The energy expenditure and inspiratory ventilation volume was subjected to analysis of variance and post hoc analysis. The ANOVA revealed a significant effect of the task reach distance, level of lift and the magnitude of weight ( p < 0.001). The plane of activity had no significant effect on metabolic cost. The increased reach of the task required 11–41% more energy and the increased load required 28–100% more energy. A high multiple correlation ( r = 0.86, p < 0.001) was achieved for the energy cost of lifting/lowering.

Physiological guidelines for the design of manual lifting and lowering tasks: the state of the art.

The goal of many researchers and practitioners of occupational health and safety has been to design manual materials handling (MMH) tasks so as to reduce the frequency and severity of overexertion injuries usually associated with these types of tasks. Physiological limits with respect to the manual lifting and lowering aspects of MMH have been reviewed and evaluated. The information provided by different researchers has been presented in a concise manner that is easily accessed by designers and practitioners of MMH. Recommendations for future research in determining physiological limits of individuals engaged in manual lifting and lowering tasks and other aspects of MMH activities have been provided.

Physiological Guidelines for the Design of Manual Lifting and Lowering Tasks: The State of the Art

The goal of many researchers and practitioners of occupational health and safety has been to design manual materials handling (MMH) tasks so as to reduce the frequency and severity of overexertion injuries usually associated with these types of tasks. Physiological limits with respect to the manual lifting and lowering aspects of MMH have been reviewed and evaluated. The information provided by different researchers has been presented in a concise manner that is easily accessed by designers and practitioners of MMH. Recommendations for future research in determining physiological limits of individuals engaged in manual lifting and lowering tasks and other aspects of MMH activities have been provided.

Visuomotor tracking performance in schizophrenia: relationship with psychopathological subtyping.

30 schizophrenic outpatients (RDC) under neuroleptic maintenance treatment completed a visuomotor tracking task with four degrees of difficulty. The mean efficiency of performance was measured in bit per second from the difference between the target signal and the tracking signal. Clinical assessment was accomplished with the BPRS, CGI, and GAS. Besides generally poorer tracking performance in schizophrenics compared with healthy volunteers the main finding was a relationship between tracking performance and psychopathological subtyping. Negative symptoms were related to a generally lowered task performance, irrespective of task difficulty. However, this effect disappeared by controlling for illness duration. On the other hand, there was a syndrome-specific interaction effect with task difficulty: Schizophrenics with positive symptoms performed poorly, especially in the most difficult task condition. Generally, there was no significant relationship between daily neuroleptic dose and tracking performance. Results are discussed with respect to a differential deficit in attention in schizophrenic subgroups.

A procedure for designing/evaluating manual materials handling tasks

A large percentage of back injuries experienced by industrial workers is the result of performing manual materials handling tasks (MMH). Therefore, manual materials handling jobs should be designed to eliminate, or to minimize, worker risk. Based on the information available in the literature, a set of MMH capacity models has been developed to accommodate: (1) various types of tasks, such as lifting, lowering, carrying, pushing, and pulling, and (2) important MMH task parameters, such as frequency of handling, height/distance of handling, box sizes, and presence/absence of handles. The models can also be adjusted for work (shift) duration, body twist, and different population percentiles. Following the development of these models, a comprehensive job design/redesign procedure was developed. A ‘risk potential’ index was also constructed to evaluate the acceptance/rejection of each task element. The procedure is demonstrated with the help of two examples.

A psychophysical study of the effect of task variables on lifting and lowering tasks: Asfour, S.S., Ayoub, M.M., and Genaidy, A.M.Journal of Human Ergology, 1984, 13.1, 3–14

A psychophysical study of the effect of task variables on lifting and lowering tasks: Asfour, S.S., Ayoub, M.M., and Genaidy, A.M.Journal of Human Ergology, 1984, 13.1, 3–14