Physical workload of flight attendants when pushing and pulling trolleys aboard aircraft

The musculoskeletal loads from moving trolleys aboard aircraft were assessed by observation of trolley handling on planes and by physical workload analyses of pushing and pulling of trolleys in a laboratory set up. Trolley handling by a total of 15 female flight attendants was observed on 10 short- and medium-distance flights in different types of aircraft. About 25 selected flight attendants (22 females; 3 males) of five German airlines took part in the laboratory study, which comprised three-dimensional (3D) measurements of posture and hand forces during pushing and pulling of trolleys in a variety of configurations. From the on-flight observations performed, between 150 and 250 trolley movements can be projected for a work shift. The greatest physical workload is to be expected at the beginning of service: The trolleys are fully laden then, and the cabin floor can still be inclined up to 8°, as the aircraft is still climbing, particularly on short-distance flights. The laboratory investigation revealed that the musculoskeletal workload from pushing and pulling depends essentially on the trolley load and on the gradient of the cabin floor. In addition, the degree of stressing depends significantly on the trolley type, mode of handling and personal dexterity. The up/down force component perpendicular to the direction of motion often achieved considerable amplitudes-in some cases equal to or exceeding the force in the direction of movement. The posture analysis demonstrated that pulling forced the flight attendants to adopt ergonomically unfavourable postures such as pronounced flexion of the back, particularly among female subjects. The highest values for flexion of the back occurred while pulling the half-size trolley. The results demonstrate that female flight attendants are likely to overload themselves if they frequently have to move heavily laden trolleys unaided on an inclined cabin floor.

Relevance to industry

On short distance flights, flight attendants have been complaining increasingly of high physical workload from manoeuvring trolleys. On the basis of the presented data airline companies may improve the trolley handling skills of their flight attendances by practical trainings and may ergonomically optimize the general service procedures aboard aircrafts.     

Muscular capabilities and workload of flight attendants for pushing and pulling trolleys aboard aircraft

Increasingly in the recent years, passengers’ services are extended into the ascent and descent flight phases on short distance flights. Trolleys containing the required meal and beverage items are used for these service operations and pushed or pulled along the aisles of the aircraft. Flight attendants reported about increased musculo-skeletal disorders and had been complaining about high physical workload from handling trolleys. In order to ensure acceptable load levels for pushing or pulling operations of trolleys, the physical capabilities of the collective “flight attendants” had been investigated by means of force measurements at maximum voluntary contraction (MVC) level and associated relevant anthropometrical and biometrical data. CEN and ISO standards as well as international and national German methods were used to derive recommended force limits for pushing/pulling operations with respect to the physical capabilities of the target group “flight attendants”. Comparing these recommended limits with the force requirements per shift under various conditions of trolley handlings (inclination of the floor, type and weight of trolley, mode of handling, frequency of operation) showed that especially for higher floor inclinations and trolley weights, flight attendants work (substantially) above recommended limits. It became also apparent that the handling of half-size trolleys is unexpectedly high demanding due to high vertical force components, caused by the unfavorable location of their center of gravity.

Relevance to industry

On short-distance flights, passengers’ services are performed by means of trolleys from the ascent to the descent flight phases. Flight attendants had been complaining about high physical workload. This study offers recommendations on maximum force limits for the handling of trolleys with respect to the muscular capacities and work situations of flight attendants on short-distance flights.     

Load on the lumbar spine of flight attendants during pushing and pulling trolleys aboard aircraft

Flight attendants report on high physical load and complaints particularly focussing on the lower back. These findings are mainly ascribed to pushing and pulling of trolleys during the ascent and descent flight phases. Within an interdisciplinary experimental study, the load on the lumbar spine of flight attendants during trolley handling aboard aircraft was analysed based on laboratory measurements regarding posture and exerted forces as well as on subsequent biomechanical model calculations. Forces and moments of force at the lumbosacral disc were quantified for 458 manoeuvres performed by 25 flight attendants in total (22 female, 3 male).Lumbar load varies according to handling mode (pushing, pulling), floor gradient (0°, 2°, 5°, 8°), trolley type (half-, full-size trolley), trolley loading (empty, medium, full) and, in addition, according to individual execution technique. For each of the resulting 48 task configurations, lumbar load was evaluated with respect to potential biomechanical overload by applying work-design recommendations for disc compression and moment of force. Irrespective of floor inclination, trolley weight and individual performance, pushing of small trolleys is combined with acceptable lumbar load, pulling with critical load. Pushing or pulling large trolleys occasionally yield to critical lumbar load, in particular, when heavy or heaviest containers are moved on relatively steep or steepest surfaces.To diminish overload risk relevantly, top-edge grasp positions should be avoided for pulling of half-size trolleys, whereas for the other cases, grasping at the upper edge of the trolley is recommended.

Relevance to industry

The provided study illustrates lumbar load of flight attendants during trolley handling aboard aircraft for typical task conditions and individual execution techniques. Specified hints for work design regarding posture and grasp position enable to avoid biomechanical low-back overload for flight attendants. Furthermore, trolley properties may be reconsidered, regular maintenance of rollers should be guaranteed.     

The effect of different surfaces on biomechanical loading of shoulder and lumbar spine during pushing and pulling of two-wheeled containers

Seven waste collectors pushed and pulled a two-wheeled container on three different surfaces: flagstones, paving stones, grass. Net torques at the shoulder joint and the lumbar spine as well as the compression and shear forces in the lumbar spine at the L4/L5 level were calculated for the tilting, initial and sustained phases. The lumbar spine compression force was below 1800N and the shear force was below 200 N in all situations. The shoulder torque when pulling with one hand was up to 80 N m. The container weight affected the magnitude of the push/pull forces and the load on the shoulders but not the load on the lumbar spine. The type of surface affected the magnitude of the push/pull forces during initial and sustained phases, and affected the load on the shoulder in the sustained phase. However, it did not affect the compression in the lumbar spine.     

Lower back muscle forces in pushing and pulling

Abstract

In the investigation of lower back stress, the muscle forces of the erector spinae and the rectus abdominis are often calculated using the two-dimensional biomechanical model. These muscle forces are used to estimate the compressive forces at L5/S1 disc This paper presents a study of the muscle forces predicted by a two-dimensional biomechanical model during pushing and pulling and myoelectric activity from the corresponding muscles. The goal was to investigate whether a simple two muscle torso model would reasonably estimate the muscle actions in pushing and pulling tasks. Six subjects participated in the experiment. EMG (rms) value was used as an indicator of muscle forces. The results show high correlation between the predicted muscle forces and the measured root-mean-square EMG values in trunk pushing and pulling (r²=0.93) and hand pushing and pulling (r²=0.96) in an erect posture with hips braced but low in hand pushing and pulling using a free posture (r²=0.37).     

Spatial dependency of shoulder muscle demands in horizontal pushing and pulling

Pushing and pulling account for nearly half of all manual material handling tasks. The purpose of this investigation was to develop a 3-D spatial muscle activity map for the right upper extremity during pushing and pulling tasks. Nineteen males performed 140 ramped directional hand exertions (70 push; 70 pull) at locations along three axes aligned with the anatomical planes. Electromyography (EMG) of 14 sites on the right upper extremity was recorded. Two directional 3-way repeated measures ANOVAs assessed the influence of hand position on EMG. Hand position and exertion direction influenced total and individual muscle demand. During pulling exertions, all three hand location parameters influenced total muscle activity (p < 0.001) and similarly in pushing exertions (p < 0.002), though less pronounced than in pulling. Data were used to create equations to predict the muscle activity of untested hand locations for novel work design scenarios.     

A different approach for the ergonomic evaluation of pushing and pulling in practice

Recent epidemiological studies show that pushing and pulling increase the risks of shoulder complaints and not necessarily of low back complaints. Moreover, the magnitude of the exerted hand forces during pushing and pulling is poorly related to the magnitude of the mechanical loading of the low back and the shoulder. In light of that, this paper combines results of several studies to present an approach for evaluating not only the exerted hand forces, but also the low back and shoulder load during pushing and pulling in practice. The approach specifies, based on scientific evidence, that (1) in order to validly obtain exposure (frequency and duration) to pushing and pulling, 10 workers should be observed during eight periods of 30 min; (2) how the exerted hand forces and the load of the low back and shoulder can be estimated in practice based solemnly on the weight of the object, one-handed or two-handed pushing or pulling, and the height of the handle; and finally, (3) how these outcomes can be evaluated in combination with existing guidelines regarding exerted hand forces, compression forces on the low back and the moments at the shoulder. Two cases will be presented here to illustrate the application of the approach.

Relevance to industry

The presented approach is the first to offer practitioners a fairly simple method for the ergonomic evaluation of pushing and pulling carts and four-wheeled containers in practice, especially as regarding the shoulder load.     

Dynamic biomechanical modelling of symmetric and asymmetric lifting tasks in restricted postures

This article describes investigations of dynamic biomechanical stresses associated with lifting in stooping and kneeling postures. Twelve subjects volunteered to participate in two lifting experiments each having two levels of posture (stooped or kneeling), two levels of lifting height (350 or 700 mm), and three levels of weight (15,20, or 25 kg). One study examined sagitally symmetric lifting, the other examined an asymmetric task. In each study, subjects lifted and lowered a box every 10 s for a period of 2 min in each treatment combination. Electromyography (EMG) of eight trunk muscles was collected during a specified lift. The EMG data, normalized to maximum extension and flexion exertions in each posture, was used to predict compression and shear forces at the L3 level of the lumbar spine. A comparison of symmetric and asymmetric lifting indicated that the average lumbar compression was greater in sagittal plane tasks; however, both anterior-posterior and lateral shear forces acting on the lumbar spine were increased with asymmetric lifts. Analysis of muscle recruitment indicated that the demands of lifting asymmetrically are shifted to ancillary muscles possessing smaller cross-sectional areas, which may be at greater risk of injury during manual materials handling (MMH) tasks. Model estimates indicated increased compression when kneeling, but increased shear forces when stooping. Increasing box weight and lifting height both significantly increased compressive and shear loading on the lumbar spine. A multivariate analysis of variance (MANOVA) indicated complex muscle recruitment schemes—each treatment combination elicited a unique pattern of muscle recruitment. The results of this investigation will help to evaluate safe loads for lifting in these restricted postures.     

A target-based population approach for determining the risk of injury associated with manual pushing and pulling

A new procedure for determining the risk of injury associated with manual pushing and pulling was developed based upon characteristics of the user population (i.e. age, gender and stature) and task requirements (i.e. working height, task frequency and travel distance). The procedure has been integrated into international (ISO, 2004) and European (CEN, 2004) standards for determining recommended force limits for pushing and pulling that can be adapted to suit the user population. These limits consider the muscular strength of the intended target population, as well as the compressive loads on the lumbar spine. Examples are provided to demonstrate variability of the proposed ‘safety’ limits for different task scenarios.

Relevance to industry

The manual handling of physical loads are known risk factors associated with work-related musculoskeletal disorders (WMSD). These disorders are common throughout the industry and may incur considerable costs to both the employer and the employee. The new risk rating procedure enables pushing and pulling tasks to be more closely aligned to the capabilities of the user population and, therefore, has an important role to play in helping to reduce the suffering and costs associated with these disorders.     

The effect of handle height and cart load on the initial hand forces in cart pushing and pulling

The objective of this study was to measure the three-dimensional hand forces people exert to initiate a cart push or pull for two cart loads: 73 and 181 kg, and three handle heights: knuckle, elbow, and shoulder heights. The cart used was equipped with 15.24 cm (6 in) diameter wheels. The floor was covered with carpet tiles. The laboratory-measured hand force exertions were compared to the minimum forces needed to push/pull the cart under the same conditions and to the psychophysical initial push/pull force limits. For pushing and pulling, the measured anterior-posterior hand forces were 2–2.4 times the minimum required forces. For the heavier cart load, lower forces were applied as handle height increased. Pull forces were 7% higher than push forces. The smallest vertical forces were measured at elbow height. Strength capability and gender did not have an effect on the applied forces. The mean strength percentile for the male sample was 64%, while the mean strength percentile for the female sample was 13% as determined from the Adjusted Torso Lift Strength Test and population strength data for this test. The comparison with the psychophysical limits indicated that the tasks were well within the maximum acceptable initial forces for males, but not for females.     

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.     

Biomechanical analysis of the effect of changing patient-handling technique

The objective of the study was to assess the changes in the mechanical load on the low-back when shifting from a self-chosen to a recommended patient-handling technique. Nine female health care workers without formal education in patient-handling carried out 8 different tasks involving moving, turning and lifting situations. By means of a dynamic 3D biomechanical model of the lower part of the body, peak torque, compression and shear forces at the L4/L5 joint were compared using the two different patient-handling techniques. In 5 of the 8 tasks, a significant reduction was observed in spinal loading. Application of the recommended technique decreased the compression value significantly for all tasks with a mean value above 3000 N. For the two tasks with the highest compression values when using the self-chosen technique (4223, 4446 N), the loading was reduced with 36% and 25%, respectively. If the principles behind the recommended technique are implemented and maintained, a decrease in the risk of low-back disorders during patient-handling should thus be expected.     

A comparison of low back kinetic estimates obtained through posture matching, rigid link modeling and an EMG-assisted model

This study examined errors introduced by a posture matching approach (3DMatch) relative to dynamic three-dimensional rigid link and EMG-assisted models. Eighty-eight lifting trials of various combinations of heights (floor, 0.67, 1.2 m), asymmetry (left, right and center) and mass (7.6 and 9.7 kg) were videotaped while spine postures, ground reaction forces, segment orientations and muscle activations were documented and used to estimate joint moments and forces (L5/S1). Posture matching over predicted peak and cumulative extension moment (p < 0.0001 for all variables). There was no difference between peak compression estimates obtained with posture matching or EMG-assisted approaches (p = 0.7987). Posture matching over predicted cumulative (p < 0.0001) compressive loading due to a bias in standing, however, individualized bias correction eliminated the differences. Therefore, posture matching provides a method to analyze industrial lifting exposures that will predict kinetic values similar to those of more sophisticated models, provided necessary corrections are applied.     

Psychophysical basis for maximum pushing and pulling forces: A review and recommendations

The objective of this paper was to perform a comprehensive review of psychophysically determined maximum acceptable pushing and pulling forces. Factors affecting pushing and pulling forces are identified and discussed. Recent studies show a significant decrease (compared to previous studies) in maximum acceptable forces for males but not for females when pushing and pulling on a treadmill. A comparison of pushing and pulling forces measured using a high inertia cart with those measured on a treadmill shows that the pushing and pulling forces using high inertia cart are higher for males but are about the same for females. It is concluded that the recommendations of Snook and Ciriello (1991) for pushing and pulling forces are still valid and provide reasonable recommendations for ergonomics practitioners. Regression equations as a function of handle height, frequency of exertion and pushing/pulling distance are provided to estimate maximum initial and sustained forces for pushing and pulling acceptable to 75% male and female workers.     

Effect of an intervention addressing working technique on the biomechanical load of the neck and shoulders among hairdressers

The purpose of this study was to describe, and analyse the effect of an intervention on, the biomechanical workload in the neck and shoulder region of female hairdressers. Arm elevation was measured by inclinometers and muscular load of m. trapezius by electromyography. The intervention comprised working technique recommendations, e.g. to work with less elevated arms and more relaxed muscles. The subjects were randomised between two different intensity levels of the intervention, one with written information only and the other with additional personal follow-up. The effect of the intervention was evaluated after 1-2 months. The hairdressers worked with their arms elevated 60 degrees or more for approximately 13% of the total working time and 16% during the specific hairdressing tasks. The intervention group including personal follow-up instructions had a reduction in workload from 4.0% to 2.5% of hairdressing time with highly elevated right upper arm, i.e. above 90 degrees . No effect was detected on muscular load or neck and shoulder symptoms after the intervention.     

The evaluation of a practical biomechanical model estimating lumbar moments in occupational activities

To estimate the mechanical load on the low back in manual materials handling, the Static Strength Prediction Model (SSPM, University of Michigan) is widely used in the occupational field. It requires (for practical reasons) only a small number of input variables (five body segment angles, standing height, total body mass, external load on the hands) on which basis the moment at the lumbo-sacral intervertebral joint (beside other parameters) is computed. The dynamic character of the activities is ignored in the calculations. To evaluate the validity of the SSPM in various situations, lumbar moments in lifting/lowering activities at different lifting techniques and speeds obtained by the SSPM, were compared with those obtained by a more comprehensive dynamic model (DM). An analysis of variance showed significant effects (p = 0.001) of the biomechanical model applied and the lifting speed used on the peak lumbar moment values. No effects of lifting technique were found. The differences in results from the SSPM and DM were dependent on the lifting speed: the SSPM peak lumbar moments were on average 9% (not significant), 21% (significant atp = 0.005) and 42% (p = 0.0001) smaller compared to the DM moments in the slow (mean velocity in a complete lifting/lowering cycle, 0.2 m s^?1), normal (0.4 m s^?1) and fast (0.8 m s^?1) speed condition respectively. The results indicate that the static/dynamic difference between the models is a major source for the different lumbar moments, while other differences between the SSPM and DM are of minor importance.     

Development of a tractor operator-operation environment coupled biomechanical model and analysis of lower limb muscle fatigue

For the quantitative analysis and evaluation of tractor pedal operation comfort, this study developed a tractor operator-operation environment coupled biomechanical model in AnyBody Modeling System. First, operator model and operation environment model were generated according to Chinese adult male anthropometric dimensions and Dongfanghong LX804 tractor design parameters. To couple these two models, the connections between operator model's palms, feet, pelvis and operation environment model's steering wheel, joystick, pedals, seat were created. The release scheme of limb joint angle constraints was designed, which allowed limbs to fulfill the kinematic requirement of operating devices. Then, to drive the model, a driver device with a rotation angle range of 0°-42°and a spring with a stiffness of 37.85Nm/rad were added to pedal hinge based on the driving data of pedal force and pedal travel collected by sensors. Subsequently, to validate the model, the surface electromyography signals of lower limb muscles were acquired using the test system of Cometa MiniWave. The average relative error between the lower limb muscle activity calculated from electromyography signals and that computed from the model was 9.2%. Finally, the model was employed to simulate the dynamic process of pedal operation and analyze lower limb fatigue. The results demonstrated that the fatigue exhibited a tendency of first decreasing and then increasing as pedal rotation angle increased, and reached a lower level within the pedal rotation angle range of 8°-17°.     

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.     

Comprehensive manual handling limits for lowering,pushing, pulling and carrying activities

The objective of this study was to develop a set of mathematical models for manual lowering, pushing, pulling and carrying activities that would result in establishing load capacity limits to protect the lower back against occupational low-back disorders. In order to establish safe guidelines, a three-stage process was used. First, psychophysical data was used to generate the models' discounting factors and recommended load capacities. Second, biomechanical analysis was used to refine the recommended load capacities. Third, physiological criteria were used to validate the models' discounting factors. Both task and personal factors were considered in the models' development. When compared to the results from prior psychophysical research for these activities, the developed load capacity values are lower than previously established limits. The results of this study allowed the authors to validate the hypothesis proposed and tested by Karwowski (1983) that states that the combination of physiological and biomechanical stresses should lead to the overall measure of task acceptability or the psychophysical stress. This study also found that some of the discounting factors for the task frequency parameters recommended in the prior psychophysical research should not be used as several of the high frequency factors violated physiological limits.     

Methodological considerations for the calculation of cumulative compression exposure of the lumbar spine: A sensitivity analysis on joint model and time standardization approaches

Cumulative lumbar spine loading has attracted much attention as a factor associated with the development of low back pain. While evidence supports cumulative loading to be a plausible mechanism in explaining several workplace injuries, research establishing a threshold limit value (TLV) for cumulative spine loading has been challenging. The lack of a TLV or even a trend towards harmful cumulative load values may suggest that methodological considerations are greatly influencing the results. This paper examines the impact of different joint models (single muscle equivalent, an electromyography-based third order polynomial, a modified version of the polynomial and a hybrid approach) to determine cumulative spine compression, as well as the importance of time standardization in the calculation of a daily cumulative loading dose. Findings demonstrated that the polynomial predicted cumulative compression values were 43–53% higher than those with all other models tested and the single muscle equivalent predicted loads 18% higher than loads predicted using a modified polynomial. Profound differences between modelling approaches suggest that caution should be taken when selecting a muscle model to determine cumulative spine compressive loading. Time standardized cumulative compression values were found to be 28.3% greater than non-standardized estimates, illustrating the importance of selecting a standard time frame in the calculation of cumulative spine compression.