Load on the lumbar spine of flight attendants - North Wales Spine ...

Abstract 

International Journal of Industrial Ergonomics 37 (2007) 863–876 

<strong>Load</strong> on the lumbar spine of flight attendants during pushing and 

pulling trolleys aboard aircraft 

Matthias Ja¨ ger a, , Kirsten Sawatzki a , Ulrich Glitsch b , Rolf Ellegast b , 

Hans Ju¨ rgen Ottersbach b , Karlheinz Schaub c , Gerhard Franz d , Alwin Luttmann a 

a Institute for Occupational Physiology at the University of Dortmund, ArdeystraX e 67, 44139 Dortmund, Germany 

b BGIA-Institute for Occupational Safety and Health, Alte HeerstraX e 111, 53757 Sankt Augustin, Germany 

c Institute of Ergonomics, Darmstadt University of Technology, PetersenstraX e 30, 64827 Darmstadt, Germany 

d Institution for Statutory Accident Insurance and Prevention in the Vehicle Operating Trades in Germany, Ottenser HauptstraX e 54, 

22765 Hamburg, Germany 

Received 20 February 2005; received in revised form 11 August 2006; accepted 18 August 2006 

Available online 30 August 2007 

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 (01, 21, 51, 81), 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. 

r 2007 Elsevier B.V. All rights reserved. 

Keywords: Push and pull; Flight attendants; Aircraft trolleys; <strong>Load</strong> on the spine; Handling recommendation 

1. Introduction 

In the context of service activities during short flights of 

commercial aircraft, flight attendants reported frequently 

on increased physical load and musculoskeletal complaints, 

Corresponding author. Tel.: +49 231 1084 267; fax: +49 231 1084 401. 

E-mail address: mjaeger@ifado.de (M. Ja¨ ger). 

0169-8141/$ - see front matter r 2007 Elsevier B.V. All rights reserved. 

doi:10.1016/j.ergon.2007.07.010 

ARTICLE IN PRESS 

www.elsevier.com/locate/ergon 

in particular, with respect to the lower back, which was 

mainly traced back to trolley handling during the ascent 

and descent flight phases. An interdisciplinary experimental 

study was conducted (Glitsch et al., 2004), followed by 

intensified evaluations on spinal-loading details (Sawatzki 

and Ja¨ ger, 2006), as adequate information on low-back 

load was not available and as musculoskeletal load in 

general was assessed hitherto only theoretically on the basis

864 

of container mass, friction, cabin inclination, and other 

task conditions. 

Previous studies were performed to quantify externalload 

indicators such as the forces applied to a transport 

cart, the handle height of the trolleys, moving speed or the 

floor properties while pushing or pulling (e.g. Winkel, 1983; 

Lee et al., 1991; Al-Eisawi et al., 1999; Laursen and 

Schibye, 2002). In other studies, knowledge on lumbar load 

is restricted on handling of carts or two-wheeled containers 

on horizontal surfaces (e.g. Mital et al., 1997; Schibye 

et al., 2001; Hoozemans et al., 2004). Specific reviews on 

pushing and pulling in relation to musculoskeletal 

disorders or ergonomic recommendations for manual 

vehicles are provided in the literature (Hoozemans et al., 

1998; Jung et al., 2005). 

The aim of the study features presented in the paper 

on hand was to quantify lumbar load, to estimate lumbar 

overload risk, to identify disadvantageous task conditions 

and to derive biomechanically substantiated hints for 

work design in order to prevent low-back overload for 

flight attendants. Other parts of the underlying crosssectional 

study deal with obtaining typical task conditions 

such as frequency and performance properties aboard 

aircraft. Adopted postures and exerted pull-or-push forces 

during trolley handling were recorded in comprehensive 

laboratory experiments (Glitsch et al., 2007), the data of 

which served as input measures at subsequent biomechanical 

model calculations for the prediction of several 

lumbar-load indicators. Subjective perception of musculoskeletal 

load and complaints were examined via questionnaires 

at a group of about 600 German flight 

attendants. Owing to guarantee a representative subsample 

of 25 flight attendants serving as subjects in the 

previously mentioned laboratory experiments, compilations 

of German airlines were examined with regard to 

biometric data of about 2,300 German flight attendants, 

and, according to the same aim, the physical strength was 

estimated via measurements on the individual forceproduction 

capability at about 500 persons (Schaub 

et al., 2007). 

2. Methods 

2.1. Experimental overview 

The quantification of the mechanical load on the lumbar 

spine of flight attendants while moving transport carts on 

inclined surfaces indispensably presumes knowledge of two 

information aspects, posture adopted and forces exerted by 

the person under study. Data gathering of these influences 

on lumbar load is essentially based on the laboratory 

experiments described in detail by Glitsch et al. (2007). As 

a sketchy insight in the experimental methodology, typical 

situations during the four basic tasks, i.e. pushing or 

pulling containers of different size, so-called full-size 

trolleys (FST) or half-size trolleys (HST), respectively, are 

demonstrated in Fig. 1. Professional flight attendants 


M. Jäger et al. / International Journal of Industrial Ergonomics 37 (2007) 863–876 

served as subjects for a couple of tasks simulating various 

conditions aboard aircraft. During performing the experimental 

procedures, the subjects wore a specific measuring 

system (‘‘CUELA’’: for further details, cf. Ellegast and 

Kupfer, 2000) containing several goniometers and inclinometers 

in order to enable continuous ambulatory recording 

of postural data, such as the flexion angle between 

forearm and upper arm or the forward bending of the 

trunk. The trolleys were equipped with several force 

sensors so that the action forces transferred via both hands 

could be registered with respect to amplitude, spatial 

direction, point of application, and temporal behaviour. 

The trolleys were pushed or pulled, in an upward 

direction, on a ramp of a length of approximately 12 m; 

this distance was not covered by a single push-or-pull 

action, but divided into three consecutive handling 

manoeuvres of few steps and inserted 5-s rest phases in 

an upright posture. In analogy to real occupational life, 

each manoeuvre was accompanied by an initial brake 

release and a final brake toggling. The ramp gradient was 

adjusted between 01, i.e. horizontal, and 81 reflecting the 

common range of aircraft pitches in the respective flight 

phase while providing meals and drinks. Intermediate 

gradients were 21 and 51. 

The weight of the trolleys has been varied in the 

experiments between unloaded and fully laden. Due to 

the different tare weights and capacities of HST and 

FST, the total mass ranged between 30 kg (HST) or 40 kg 

(FST) in case of empty containers and reached up to 60 kg 

(HST) or 90 kg (FST) for completely loaded trolleys, 

respectively. Forty-five and 65 kg were chosen as intermediate 

conditions. 

In the laboratory experiments, 25 voluntary and healthy 

flight attendants participated. According to the high 

proportion of women in Germany working as a flight 

attendant in relation to men, 22 female and 3 male subjects 

took part in the measurements. The variety and complexity 

of the experimental procedures caused separate days for 

each subject. All persons performed the same battery of 

tasks, if being able. 

The variation of the mentioned task parameters totally 

resulted in 48 different experimental configurations, i.e. 

two handling modes, two trolley types, three trolley 

masses, four floor gradients were applied. Considering 

the sample of 25 subjects and three manoeuvres per trial, in 

total, 3,600 actions of a length of 3–10 s were recorded. 

Invalid trials, for example, due to insufficient muscular 

capacity or unsuitable footwear to perform a high-loading 

task like handling a heavy trolley on an 81 inclined surface, 

let diminish the total number to 3,410 of usable periods. 

2.2. Data recording 

The sample rate of all signals was set to 50 Hz. In 

consequence, the diverse indicators of kinematics or 

kinetics provided in the following were stored for every 

20 ms, corresponding time courses were generated by

FST 

full- 

size 

trolley 

HST 

half- 

size 

connecting adjacent points. In order to enable succeeding 

comparison of various tasks with respect to resulting 

lumbar load, time courses were ‘‘low-pass filtered’’ by a 

200-ms moving average, i.e. mean values at every 20 ms 

were calculated for 10 consecutive points. 

2.2.1. Posture 

Manifold information on the posture of a flight 

attendant was registered while performing the push-or-pull 

manoeuvres in the laboratory. The applied CUELA system 

enabled the recording of 26 postural indicators over time. 

The positions of the legs were described by four measures, 

eight indicators were related to the trunk and head, and 14 

parameters were concerned to the shoulders, arms and 

hands. These indicators mainly represent ‘‘relative angles’’ 

between adjacent body segments to describe the graduation 

of joint flexion or, only in the case of trunk inclination 

against gravity, ‘‘absolute angles’’. Enabling data usage for 

the intended subsequent lumbar-load prediction via the 

biomechanical analysis tool ‘‘THE DORTMUNDER’’ (Ja¨ ger 

et al., 2001), conversion into an inertial co-ordinate system 

was necessary. 

2.2.2. Action forces at trolley and hands 

The forces applied at the trolley during pushing or 

pulling were recorded via sensor-equipped bars fixed to the 

trolley. The bars were positioned individually for each trial 

according to the preferred grasping manner stated by the 


M. Jäger et al. / International Journal of Industrial Ergonomics 37 (2007) 863–876 865 

trolley 

pushing pulling 

Fig. 1. Typical situations in the laboratory for posture and force recording during trolley handling. 

respective attendant: two bars vertically at the lateral edges 

of the trolley, because the person commonly varies the 

grasp height, or one bar horizontally at the upper trolley 

edge if the attendant preferred grasping at the top. At the 

handles, three-axial force sensors were inserted at both 

ends so that the longitudinal, vertical and transversal 

components could be recorded. The longitudinal component 

represents the motion-directed push-or-pull force, the 

vertical components shows the person’s leaning upon the 

trolley or, inversely directed, a lifting force, and the 

transversal force component indicates the force pointing 

to lateral. In maximum, 10 force-related signals were 

continuously registered. Recording of only 10 out of 12 

signals is based on the fact that at each handle the force 

pointing to the bar’s length axis is not measured twice, but 

only once. 

At one bar, the sum of the two force signals for an 

identical direction lead to the resultant force component at 

the respective hand. The distribution of the forces, 

recorded by the two sensors at the same bar, allowed the 

local determination of the point of force application. This 

indicator enabled the verification of the grasp-point 

localization predicted by the postural measurements via 

gonio- and inclinometers at the body. For the following 

biomechanical lumbar-load predictions, the three force 

components for both hands were used as input data after 

angle conversion due to the trolley’s oblique orientation 

while moving on an inclined surface.

866 

2.3. Indicators of lumbar load 

Computerized calculations for quantifying measures of 

lumbar load were performed which were based on the 

recorded data on posture and exerted hand forces, both 

varying in the course of a push-or-pull action, as described 

above. Individual stature and body mass, ranging between 

the 5th and 95th percentiles of the sample ‘‘German flight 

attendants’’, were considered (cf. Schaub et al., 2007). 

Several mechanical indicators of lumbar load, i.e. the 

bending and torsional moments of force or the compressive 

and shear forces at the lowest intervertebral disc of 

the spine, were predicted applying a previously developed 

‘‘biomechanical model’’. As common in comparable 

ergonomic investigations, the lumbosacral disc ‘‘L5–S1’’— 

the transition between the 5th lumbar and the 1st sacral 

vertebrae, the latter representing the upper part of the 

sacrum—was chosen as the reference point due to its 

relatively high disease prevalence and biomechanical overexertion 

risk. The indirect method of biomechanical 

modelling was applied, since direct determination via 

invasive measurement of mechanical indicators of lumbar 

load such as the intradiscal pressure (e.g. Nachemson and 

Elfstro¨ m, 1970; Wilke et al., 1999) cannot be performed in 

ergonomic investigations for ethical reasons. 

2.3.1. Biomechanical modelling 

The basic approach, the underlying procedures and 

details on the modellings of the skeletal and muscular 

structures, of intra-abdominal-pressure efficacy and of 

inertia effects are described formerly (cf. Ja¨ ger et al., 1991, 

2001); a few aspects provided in the following may give a 

sketchy insight. 

A spatial dynamic multi-segmental biomechanical model 

(‘‘THE DORTMUNDER’’) was used for quantifying the lumbar 

load during trolley handling. The human skeletal structure 

in this analysis tool is represented by 30 rigid body 

segments, 14 of which are located within the trunk 

according to the location of the intervertebral discs 

between pelvis and shoulder-joint height (T3–T4); in the 

superior joint, a neck–head segment is connected. Individual 

postures are replicated via angle variation in up to 26 

joints, which particularly enables the imitation of realistic 

spinal curvatures via sagittal and lateral flexion as well as 

twisting. Foot, lower and upper legs, shoulder, upper arm 

and forearm as well as hand are included in the model 

bilaterally. 

The muscular structure in the lower trunk region which, 

in particular, is spread over the lumbar discs, is replicated 

by the effect of 14 muscles or muscle cords in total: the 

Longissimus Thoracis and Iliocostalis Lumborum as 

relevant cords of the Erector Spinae muscle group at the 

back, and the Rectus abdominis as well as the medial and 

lateral parts of both the External and Internal Obliques at 

the frontal side. Their functional effects correspond to nine 

‘‘muscle equivalents’’ or ‘‘resultant force vectors’’ in 

anatomically justified distances. The mathematical problem 



of redundant muscle force distribution is solved via a linear 

optimization technique. 

The effect of trunk stabilization according to intraabdominal 

pressure is considered in the model by referring 

to the measurements of Morris et al. (1961) and the 

consecutive evaluations of Chaffin (1969). For purposes of 

validation, for example, specific electromyographical measurements 

were performed, the underlying top-down 

principle in THE DORTMUNDER was compared to 

corresponding bottom-up application, and, where possible, 

results of modelling were verified by findings from 

measurements of lumbar intradiscal pressure (Nachemson, 

1966; Andersson et al., 1977; Wilke et al., 1999). 

The model was applied ‘‘quasi-statically’’, i.e. the action 

forces during trolley handling included the inertial effects, 

however, acceleration of body segments’ masses remained 

unconsidered in this study. A sample of 468 out of 3,410 

usable actions was analysed with regard to the prediction 

of several mechanical indicators of lumbar load. Selection 

was performed arbitrarily in principle, but under the 

restrictions to receive data for each of the 48 different task 

configurations in total and to reject trials involving 

uncommon handling performance with respect to posture 

(e.g. twisted), force exertion (e.g. single-handed) or, in 

some cases, gliding foot. 

2.3.2. Evaluation criteria 

The mechanical load on the lumbar spine during trolley 

handling is described on the basis of force and moment of 

force acting at the lumbosacral disc. For both indicators, 

classification approaches provided in the literature are 

applied, as customary in ergonomics and occupational 

health in the assessment of activities involving lumbar load. 

Based on total values for the vectorial quantity ‘‘moment 

of force’’, Tichauer (1978) provides moment categories with 

relevance to the selection and training of working persons or 

to the adherence of rest brakes. This classification is based on 

decades of experience of load analyses in ergonomic and 

biomechanical studies with a special emphasis on muscle 

physiology and lumbar-load model calculations. The limit 

values 40, 85 and 135 N m serve for defining the respective 

classes. According to Tichauer’s specifications, a criterion of 

85 N m was chosen for the evaluation of moment values 

resulting for flight attendants while trolley handling. The 

properties ‘‘good body structure’’ and ‘‘some training’’ were 

attributed to that group of working persons, whereas 

‘‘selective recruitment of labour’’ regarding musculoskeletal 

or cardiopulmonary performances, ‘‘careful training’’ and 

‘‘attention to rest pauses’’ were estimated as too severe 

conditions. An incorrect, too insensible categorization would 

be carried out, if flight attendants—according to the 3rd 

category of Tichauer—were described as ‘‘untrained’’ or 

‘‘irrespective of body build’’. In total, the 85-N m criterion 

was applied to the sagittal–moment component, since this 

direction clearly dominates the total moment in the analysed 

spectrum of tasks, i.e. pushing or pulling on a straight way 

(Glitsch et al., 2004).

Evaluation of the reaction forces acting at the lumbosacral 

disc is focussed on disc compression, as valid 

comparable criteria regarding the other components, i.e. 

sagittal and lateral shear, are more or less not available (cf. 

Mital et al., 1997; Ja¨ ger, 2001). The disc-compression 

criterion applied in this paper is derived from the so-called 

DORTMUND RECOMMENDATIONS, which represent age-andgender-specific 

limits during occupational work (Ja¨ ger and 

Luttmann, 1997). The provided values are based on 

numerous measurements on the load-bearing capacity of 

autopsy material dissected from human lumbar spines, 

subsequent gender-specific regression analyses over age 

and, in order to avoid overestimation of individual’s spinal 

load-bearing capacity, a decrement insertion as a safety 

margin. 

The recommended limits range between 2.3 kN for males 

as from an age of 60 years and 6.0 kN for 20-year-old male 

adults or, in case of females, between 1.8 and 4.4 kN for 

older or younger persons, respectively. Considering the 

huge majority of women, on the one hand, and the age 

distribution of German flight attendants (cf. Schaub et al., 

2007), in accordance with the 95th percentile a value of 

2.5 kN was ultimately chosen as the criterion for evaluating 

disc compression during trolley manoeuvres. 

This approach of comparing predicted disc compression and 

the mechanical strength follows the idea of the well-known 

5° 

80 


FST 

fullsize 

trolley 

0 

0 1 2 3 4 5 6 7 

65 kg -80 

upward + / downward - 

leftward + / rightward - 

HST 

halfsize 

trolley 

60 kg 

80 

‘‘Work Practices Guide for Manual Lifting’’ (NIOSH, 1981; 

Waters et al., 1993), the application of which, however, seems 

inadequate for evaluating pushing and pulling activities. 

Furthermore, the NIOSH criterion is only weakly supported 

by both its epidemiological and biomechanical sources, and 

the underlying data base regarding mechanical-strength tests 

is smaller by a factor of approximately30incomparisonto 

the DORTMUND RECOMMENDATIONS (Ja¨ ger and Luttmann, 

1999). 

3. Results 

3.1. Typical temporal behaviour 

3.1.1. Action forces at trolley and hands 

Fig. 2 shows typical time-course sections of about 6–8 s 

for the action forces at the hands recorded at the 

laboratory experiments for exemplary manoeuvres. The 

examples represent pushing (left) or pulling (right) of FST 

(above) or HST (below) of similar mass (65 kg vs. 60 kg) on 

a51 inclined surface, performed by the same subject. With 

respect to the four basic tasks in Fig. 2, each diagram 

includes six curves according to bi-lateral registrations of 

the longitudinal, vertical and lateral directions. 

As the diagrams show, all action–force time courses are 

characterized by a ‘‘rough’’, unsteady behaviour: most of 

action forces at the hands in N 


forward + / backward - 



5 s 

leftward + 

rightward - 

0 

0 1 2 3 4 5 6 7 8 

-80 


8 

80 



0 

0 1 2 3 4 5 6 7 8 

-80 

80 



0 

0 1 2 3 4 5 


6 7 8 

-80 


time in s 

Fig. 2. Typical time courses for action forces at the hands during trolley handling, performed by the same subject. Note: continuous lines, right hand; 

broken lines, left hand.

868 

the curves demonstrate a steep increase after a 1-s 

preparation phase, when an adequate posture was adopted, 

the trolley was prepositioned and the muscular tension for 

the subsequent force exertion in order to set the trolley in 

motion were terminated. During the main activity of 

pushing or pulling, the curves show a more or less 

horizontal tendency including step-induced changes. In 

the later phases, a weaker decrease during retardation 

caused by friction and gravity can be observed. In addition, 

the upper-left diagram clearly shows the reaction on 

toggling the brake via a foot motion by a local maximum 

at the time 6–7 s in the courses for the vertical hand-force 

component: a 40-N force pointing downwards, i.e. showing 

a negative value, is changed to a maximum value of about 

50 N in upward direction in this phase. In a first attempt, 

the corresponding curves for the left and right hands show 

similar results for identical task conditions; larger differences 

are mainly attributed to unequal tasks or differing 

components of the action forces, as the examples in Fig. 2 

illustrate. 

Excepting the case of pulling the HST (lower right), 

the highest forces of up to 120 N were gathered for the 

forward–backward component, i.e. the component in the 

direction of motion while pushing or pulling. Considering 

the assumed co-ordinate system, pushing leads to positive 

values and pulling to negative values regarding the 

forward–backward component. In contrast to highest peak 

values for the sagittal force component, the lowest force 

5 ° 

FST 

fullsize 

trolley 

65 kg 

HST 

halfsize 

trolley 

60 kg 

2 

1 


peak, reaching up to 25 N, were found for the lateral 

component, i.e. for the steering actions. Intermediate 

values were recorded for the vertical forces; in the 

respective curves, distinct local maxima in the upward 

directed forces after about a second can be identified which 

is traced back to ‘‘partial lifting’’ in order to overcome 

resting state. 

The force-component pattern in the case of pulling a 

HST obviously differs from the force distribution in the 

other three cases shown in Fig. 2: besides the anyhow high 

forces in pulling direction, high forces in upward direction 

were permanently exerted during the main phase. This 

activity is ascribed to the fact that the small HSTs can be 

tilt by relatively low horizontal forces if applied at the 

upper edge. To prevent tilting while pulling, the persons 

superimpose considerable upward forces to the horizontal 

sagittal force so that the sum of both enables stability. 

With respect to the provided example, the vertical forces 

for ‘‘backdrop lifting’’ even exceed the underlying horizontal 

forces for pulling (approximately 70–120 N vs. 

50–80 N). 

3.1.2. Indicators of lumbar load 

The mechanical load on the lumbar spine of flight 

attendants during moving meal-and-drink containers is 

exemplarily indicated in Fig. 3. In the upper part of the 

diagram, the time courses for the reaction forces acting at 

the lumbosacral disc for handling a FST of a total mass of 


sagittal shear 

0 

0 1 2 3 4 5 6 7 8 

lateral shear 

2 

1 


compression 


reaction forces at L5-S1 in kN 

sagittal 

shear 

0 

0 1 2 3 4 5 

lateral shear 

6 7 8 

0 

0 

0 1 2 3 4 5 6 

lateral shear 

7 8 0 1 2 3 4 5 

lateral shear 

6 7 8 

5 s time in s 

2 

1 

2 

1 





Fig. 3. Typical time courses for predicted reaction forces at the lower spine during trolley handling, performed by the same subject.

65 kg on a 51 inclined floor is drawn, and the corresponding 

curves for moving a 60-kg HST are shown in the lower 

part. On the left-hand side, push-related results are 

marked, whereas pull-related lumbar load is provided on 

the right-hand side. In each of the diagrams, the temporal 

behaviour of the components of the reaction force in three 

orthogonal disc-related directions are shown: the axial 

compression as well as sagittal and lateral shear. In total, 

the L5–S1 reaction–force time courses in Fig. 3 correspond 

to the curves in Fig. 2 for the action–forces applied at the 

hands during pushing or pulling the identical containers by 

the same person. 

As demonstrated in Fig. 3, disc compression shows to 

the highest force values in comparison to the two shearforce 

components. The sagittal shear force was throughout 

higher than the lateral component in all four cases. The 

compressive-force curves show a pronounced maximum 

after the initial phase for prepositioning the body and the 

trolley. The compression-related peak values gathered for 

the four cases in Fig. 3 vary between approximately 1.7 and 

2.7 kN, both of which are related to pulling manoeuvres. 

Step-induced changes revealing in more or less ‘‘unsteady 

curves’’ are more distinct for pushing than for pulling in 

these examples. The highest disc compression forces during 

the ‘‘main phase of continuous moving’’ resulted for 

pulling the HST, which might be attached to the 

corresponding action force pattern showing strong verticalforce 

exertion throughout pulling a HST (cf. lower-right 

diagram in Fig. 2). 

3.2. Effects of various task conditions on lumbar load 

Replication of real-life task conditions in the investigation 

of lumbar load for flight attendants while trolley 

handling lead to the consideration of 48 ‘‘task configurations’’ 

representing different combinations of various 

container types and masses as well as several floor 

gradients during the pushing or pulling experiments in 

the laboratory. In analogy to the time courses provided in 

Fig. 3, 468 complete manoeuvres were analysed with regard 

to lumbar load. The results of the lumbar-load prediction 

calculations are summarized in Fig. 4 based on the peak 

values of the respective moving-averaged time courses. 

In the upper part in Fig. 4, effects of various task 

conditions are demonstrated with respect to lumbosacral 

compressive forces (F c), whereas the lower part shows the 

corresponding relations by means of the indicator ‘‘sagittal 

moment of force’’ (Ms). Both parts are organized in 

analogy to Figs. 2 and 3: the two diagrams above are 

related to FSTs and the two lower ones to half-size 

containers; on the left-hand side, the effects of pushing are 

visualized and pulling-related results on the right-hand 

side. Each of the eight diagrams in total shows the 

dependency of the respective lumbar-load indicator, i.e. 

compression or sagittal moment, vs. trolley mass for 

various floor gradients. The symbols and bars represent 

mean and standard deviation values for the respective task 



configuration. For purposes of clearness, in Fig. 4, the 

underlying number of analysed manoeuvres per configuration 

(n) is included in the lower part in Fig. 5 (range of n: 

3–17, median: 9). In spite of the low numbers of 

measurements for 3 of 48 configurations (n: 3 or 4) and 

in spite of the reserve of mere statistics, the respective 

standard deviation values are nevertheless provided to 

enable easy comparability in Fig. 4. 

The diagram in the upper-left corner in Fig. 4 

demonstrates the effects of various container weight and 

floor inclination on lumbosacral-disc compressive force 

during pushing FSTs. As the regression lines illustrate, 

lumbar load clearly increases with both increasing mass 

and increasing gradient, and the line’s slope is more 

pronounced for steeper inclination than for a horizontal 

surface. That means, the higher the mass and/or the higher 

the gradient, the higher the resultant lumbar-disc compression. 

These effects—related to disc compression and 

FSTs—can also be identified in the corresponding moment 

regressions over trolley mass (cf. lower part in Fig. 4, 

upper-left diagram) and, but not as distinct as for pushing 

FSTs, in analogous cases of pushing HSTs (cf. lower-left 

diagrams). 

The results for lumbar load received from the measurements 

during pulling FSTs or HSTs are not as evident 

as for pushing so that the regression lines in the respective 

diagrams may intersect among one another (cf. the 

four diagrams in the right part in Fig. 4 vs. the four left 

diagrams). On the one hand, the regressions show an 

inclination vs. trolley mass, however, lumbar load does not 

increase with floor steepness, on the other hand. The latter 

effect is particularly evident for pulling HSTs so that, for 

example, pulling an empty HST on a horizontal surface 

leads on average to higher values of lumbar load than 

pulling it on an 81 inclined floor. 

Regardless of the specific effects of trolley mass and floor 

gradient on lumbar load, overall comparison for the four 

basic tasks shows highest values for pushing full-size and 

pulling HSTs, whereas pulling FSTs and pushing HSTs 

resulted in lower values for both disc compression and 

moment. These results include the particular feature that 

pulling the smaller HSTs lead to higher lumbar load 

than pulling the larger full-size containers, although the 

laden FSTs were heavier than the laden HSTs on average 

(see also Figs. 2 and 3). Fig. 4 clearly illustrates 

furthermore that the influence of gradient variation is 

highest for pushing FSTs and lowest for pulling those large 

containers. 

4. Discussion 

4.1. Evaluation of lumbar load 

Lumbar load with respect to biomechanical overload for 

flight attendants during trolley handling is evaluated in 

detail by application of two pairs of criteria, the results of 

which are subsequently summarized to illustrate the main

870 

FST 

fullsize 

trolley 

HST 

halfsize 

trolley 

FST 

fullsize 

trolley 

HST 

halfsize 

trolley 

effects. The definitions of the criteria were derived 

following the premises of plausibility and common sense. 

4.1.1. Evaluation criteria 

As described in Section 2, the results for both lumbar-load 

indicators—compressive force (Fc) and sagittal moment (Ms) 

at the lumbosacral disc—are compared to the corresponding 



4 

3 

2 

1 

0 

4 

3 

2 

1 

0 

200 

150 

100 

50 

0 

200 

150 

100 

50 

0 

compressive force on L5-S1 (Fc) in kN 


0 

40 kg 65 kg 90 kg 40 kg 65 kg 90 kg 

0 

30 kg 45 kg 60 kg 

30 kg 

4 

3 

2 

1 

4 

3 

2 

1 

8 ° 

5 ° 

2 ° 

0 ° 

45 kg 

60 kg 


40 kg 65 kg 90 kg 

sagittal moment at L5-S1 (Ms) in Nm 

200 

150 

100 

0 

30 kg 45 kg 60 kg 30 kg 45 kg 60 kg 

50 

0 

200 

150 

100 

50 

8 ° 

5 ° 

2 ° 

0 ° 

recommended lumbar-load limits (LLL), i.e. 2.5 kN or 

85 N m, respectively. In addition, potential exceeding a limit 

by a single person or several subjects for a certain task 

configuration is rated via two further criteria, which illustrate 

the ‘‘frequency’’ or the ‘‘intensity’’ of target overshooting by 

the three categories ‘‘acceptable’’, ‘‘occasionally critical’’ or 

‘‘critical’’ lumbar load. That means for each of the 48 task 

8 ° 

5 ° 

2 ° 

0 ° 

40 kg 65 kg 90 kg 

Fig. 4. Predicted lumbar load, represented by two indicators (upper/lower part), during pushing and pulling of trolleys considering various weights and 

different inclinations (numbers of analysed manoeuvres per task configuration: see Fig. 5, lower part). 

8 ° 

5 ° 

2 ° 

0 °

configurations that both the so-called frequency criterion 

(Cf) and the so-called amplitude criterion (Ca) are applied on 

the value ranges for both lumbar-load indicators (Cf[Fc], 

Cf[Ms], Ca[Fc], Ca[Ms]). 

The lowest category of the frequency criterion (‘‘acceptable’’) 

is fulfilled for an examined sub-sample of the size 

‘‘n’’, if the number of manoeuvres ‘‘n + ’’—combined with 

higher compressive force or sagittal moment than the 

respective lumbar-load limit—is, in maximum, 1; or, in 

other words, the respective lumbar-load limit is never 

exceeded (n + ¼ 0) or one time (n + ¼ 1). According to 

these cases, the manoeuvres were performed by all or 

almost all subjects in such a way that the resulting lumbarload 

values did not exceed the recommended limits for 

work design. By contrast, the highest Cf category 

(‘‘critical’’) is valid when more than half of all manoeuvres 

leads to lumbar load above the respective limit (n/2on + ), 

assuming an identical task configuration. Limit exceeding 

occurring two times up to the half of all manoeuvres 

(2pn + pn/2) would lead to the intermediate category 

(‘‘occasionally critical’’). 

In summary, the categories of the frequency criterion C f 

were defined as follows: 

lumbar load according to Cf ‘‘acceptable’’ nþp1; lumbar load according to Cf ‘‘occasionally critical’’ 2pnþpn=2; lumbar load according to Cf ‘‘critical’’ n=2onþ : 

If the value ‘‘mean plus standard deviation’’ (m+S.D.) 

for a certain task configuration is lower than the 

recommended lumbar-load limit (m+S.D.oLLL), the 

‘‘acceptable’’ category of the amplitude criterion is valid. 

Such a group of data implies that lumbar load was 

preponderantly lower than the respective limit and that the 

intensity of a potential limit exceeding was not high enough 

to predominate the main result. The ‘‘critical’’ Ca category 

is fulfilled in cases, if the mean value exceeds the fixed limit 

for lumbar load (LLLom). That means that the amplitudes 

of lumbar load during trolley handling under the 

respective circumstances were on average higher than the 

corresponding recommendations for work design. Assuming 

lumbar load of intermediate intensity (mpLLLp 

m+S.D.), i.e. lumbar load was partly higher than the 

respective limit to a considerable, but non-predominant 

extent, a categorization ‘‘occasionally critical’’ resulted for 

this task configuration. This implies that the main part of 

sample’s lumbar load falls below the recommended limit 

for work design. 

In summary, the following specifications were stipulated 

for the categories of the amplitude criterion Ca: 

lumbar load according to Ca ‘‘acceptable’’ m þ S:D:oLLL; 

lumbar load according to Ca ‘‘occasionally critical’’ mpLLLpm þ S:D:; 

lumbar load according to Ca ‘‘critical’’ LLLom: 

Application of the frequency and amplitude criteria on 

the results for disc compression or sagittal moment (Cf[Fc], 



Cf[Ms], Ca[Fc], Ca[Ms]) of totally 468 manoeuvres, grouped 

for 48 task configurations, is demonstrated in the upper 

part in Fig. 5. According to the four basic tasks—pushing 

or pulling FST or HST—and to the four floor gradients 

and three loading states, Fig. 5 shows 192 cells in total, 

resulting from the detailed evaluations (four criteria times 

48 configurations). This evaluation induced various results 

for the four basic tasks, as the different patterns show: the 

white cells in the lower-left diagram indicate that pushing a 

small container leads to ‘‘acceptable’’ lumbar load for all 

task conditions, i.e. irrespective of trolley loading, surface 

inclination and individual performance. For pulling a HST 

(lower-right diagram), however, dark cells dominate which 

corresponds to ‘‘critical’’ lumbar load for the respective 

task configuration. The uppermost diagrams, representing 

the evaluation of moving the large containers in both 

handling modes, indicate ‘‘occasionally critical’’ lumbar 

load for a couple of task configurations, in particular, for 

heavy trolleys moved on relatively steep surfaces. 

4.1.2. Summarization 

The quadruple results of the detailed evaluation for each 

of the 48 task configurations (cf. upper part in Fig. 5) were 

summarized in order to clarify systematic behaviour and to 

enable the derivation of justified work-design measures 

(cf. lower part in Fig. 5). 

In the case of task conditions combined with prevailing 

acceptable lumbar load, the corresponding work was 

assessed being ‘‘uncritical’’ or ‘‘acceptable’’ so that no 

redesign seems necessary. This lumbar-load category is to 

be assumed if none of the two pairs of criteria (Cf[Fc], 

Cf[Ms] andCa[Fc], Ca[Ms]) is exceeded or if, at most, one of 

the four leads to an ‘‘occasionally critical’’ load evaluation. 

The latter aspect implies, besides three acceptable share 

evaluations, that either at best one of all manoeuvres 

performed by several flight attendants under the respective 

task condition resulted in an overshooting of one of the 

recommended lumbar-load limits for disc compressive 

force or sagittal moment of force (Cf: n + p1). Or the 

intermediate category for the amplitude criterion (Ca: 

mpLLLpm+S.D.) is fulfilled regarding one of the two 

load indicators (Fc, Ms), i.e. the main part of sample’s 

lumbar load falls below the respective recommendation for 

disc compression or moment. 

In contrast to acceptable lumbar load, the summarization 

procedure leads to an overall assessment ‘‘critical’’ if, 

at least, one of the four share estimations resulted in the 

categorization ‘‘critical’’. This summarization rule implies 

that the other detailed evaluations are ignored due to the 

highly assumed impact of one critical share-estimation: 

either most of the manoeuvres yielded to exceeding one of 

the lumbar-load limits (Cf: n/2on + ), or the mean value for 

disc compression or moment excelled the respective limit 

(C a: LLLom). Measures of work design are urgently 

recommended. 

Finally, the rules for an intermediate categorization after 

summarizing the detailed evaluations are described: none

872 

FST 

fullsize 

trolley 



FST 

fullsize 

trolley 

HST 

halfsize 

trolley 

HST 

halfsize 

trolley 

8 ° 

5 ° 

2 ° 

0 ° 

8 ° 

5 ° 

2 ° 

0 ° 


Fc: compressive force Ms: sagittal moment 

8 ° 

5 ° 

2 ° 

0 ° 

8 ° 

5 ° 

2 ° 

0 ° 

40 kg 65 kg 90 kg 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 

Fc Ms Fc Ms Fc Ms 

30 kg 45 kg 60 kg 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 


summarization 


40 kg 65 kg 90 kg 

9 

12 

30 kg 45 kg 60 kg 

29 

8 12 13 33 

6 10 14 30 

n = 13 10 17 40 

N = 36 44 52 132 

9 10 15 34 

13 7 13 33 

8 7 15 30 

n = 4 10 12 26 

N = 34 34 55 123 

detailed evaluation 

8 

8 ° 

5 ° 

2 ° 

0 ° 

8 ° 

5 ° 

2 ° 

0 ° 

8 ° 

5 ° 

2 ° 

0 ° 

8 ° 

5 ° 

2 ° 

0 ° 

40 kg 

65 kg 90 kg 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 


30 kg 45 kg 60 kg 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 

Cf 

Ca 


40 kg 65 k g 90 k g 

10 10 3 23 

9 11 9 29 

10 12 10 32 

n = 6 10 10 26 

N = 35 43 32 110 

30 kg 45 kg 60 kg 

9 5 

4 9 

7 5 

23 

25 

27 

n = 7 9 12 28 

N = 27 28 48 103 

Fig. 5. Evaluation of lumbar load for studied task configurations. Note: lumbar load acceptable (white), occasionally critical (grey), critical (dark). Upper 

part: detailed evaluation for both load indicators (Fc, Ms) and both ratings (Cf, Ca). Lower part: resultant assessment by summarizing the above shareevaluations. 

Numbers (n, N) indicate the sample sizes for the diverse experimental configurations. 

9 

12 

15 

Cf: frequency criterion 

Ca: amplitude criterion

of the share estimations is critical, and two up to four 

occasionally critical evaluations are present implying the 

complementary categories being acceptable. Measures of 

work design should be considered and are recommended 

‘‘from case to case’’. 

In total, the following rules were applied in the 

summarization procedure: 

Overall lumbar 

load 

Cf[Fc], Cf[Ms], Ca[Fc], Ca[Ms] 

‘‘acceptable’’ 4 ‘‘acceptable’’ 

or 3 ‘‘acceptable’’, 1 ‘‘occasionally 

‘‘occasionally 

critical’’ 


‘‘critical’’ X1 ‘‘critical’’ 

2 ‘‘acceptable’’, 2 ‘‘occasionally 


or 1 ‘‘acceptable’’, 3 ‘‘occasionally 


or 4 ‘‘occasionally critical’’ 

Application of the summarization rules on the detailed 

evaluations regarding the 48 task configurations is illustrated 

in the lower part in Fig. 5. Moving HSTs yields to very clear 

assessments, even if controversial for the two handling 

modes: pushing is combined with acceptable lumbar load, 

pulling with critical load, irrespective of the graduations of 

floor inclination and trolley loading or irrespective of 

individual performance. Pushing FSTs were assessed to be 

occasionally critical or critical for three configurations each. 

Pulling FSTs is less critically assessed: once critical and four 

times occasionally critical. In the case of FST moving, the 

category ‘‘critical’’ is valid, if at all, for moving heavy or 

heaviest containers on steep or steepest surfaces. 

4.2. Biomechanically justified work design 

The manifold results for lumbar load were previously 

analysed with respect to the various task conditions and 

their graduations. The diverse evaluation approaches 

discovered, in particular, biomechanical overload for 

pulling HSTs as well as for a few other configurations 

representing heavy trolley loading or considerably inclined 

surfaces. However, having the individual results in view, it 

is evident that performance was not strictly combined with 

high lumbar-load values and that some subjects were 

obviously able to move the trolley in an advantageous 

manner. Besides individual performance characteristics, 

the actual trolley design may be improved to support 

ergonomic handling. 

4.2.1. Handling technique 

In order to derive biomechanically justified hints and 

ergonomically acceptable handling techniques, pairs of 

manoeuvres resulting in extreme disc compression, either 

minimum or maximum values, were selected for identifying 

relevant differences in individual performances; such 



comparisons were performed regarding the high-loading 

task configurations (medium/heavy, 51/81) for both trolley 

types (HST, FST) and handling modes (pushing, pulling). 

A typical example of paired comparisons is shown in 

Fig. 6, providing the time courses of the action forces 

applied at the hands in the upper part and the analogous 

curves of the disc-related reaction forces below. On the lefthand 

side, the results of the manoeuvre combined with the 

lowest disc-compression peak value are demonstrated, 

whereas the right-hand side corresponds to the highest 

peak of the same sub-sample ‘‘pulling a 60-kg HST on a 51 

inclined surface’’. The compression curves illustrate that 

the resulting lumbar load may vary to a very considerable 

extent due to individual technique: related to the example 

in Fig. 6, compression ranges between nearly 2 and 5.5 kN. 

The corresponding hand–force curves show a similar 

behaviour: low forces in the left, much higher ones in the 

right. This aspect may be attributed to the underlying 

postures, which can significantly be referred to the grasp 

points at the trolley. As sketched in the top line in 

Fig. 6, grasp localization differed noticeably. A low grasp 

position (see left-hand part of Fig. 6) helps to keep stable 

movement of the relatively ‘‘shaky’’ HST, whereas grasping 

at the top edge (see right) corresponds to a long vertical 

lever arm. This would yield to easily tilting, which is, 

however, avoided by the subject by supplementary upwarddirected 

action forces, as mentioned in the context of 

Figs. 2 and 3. 

Application of this methodology of paired comparison 

to all of the 16 selected sub-samples—representing each 

lumbar-load values for manoeuvres performed by several 

flight attendants in various task configurations—lead to the 

following systematic results without any contradiction: 

pulling a half-size container yields in lower disc compression 

for grasping at a low position, whereas all other tasks 

(HST pushing, FST pushing/pulling) are combined with 

low compression values in case of grasp points at the top 

edge. These effects can be traced back in pushing activities 

to the possibility to lean the body on the container and, 

thereby, to reduce the back loading induced by body 

weight. During pulling a full-size container, the HSTspecific 

upward-directed action forces, applied to avoid 

tilting, are unnecessary according to the FST’s length 

supporting stability. Furthermore, lower grasping would 

force disadvantageous posture with more pronounced 

trunk inclination or knee flexion. 

4.2.2. Trolley properties 

The hand forces applied to the trolley were measured in 

the laboratory experiments via specifically established bars, 

which were fixed to the containers. In real life, however, 

such handgrips supporting adequate handling do commonly 

not exist (cf. Glitsch et al., 2007). Besides simple, 

rigid bars, solid frontal pull-out trays could also be 

mounted so that, in particular, the effective base area of 

the short HST is virtually enlarged in moving direction 

and, thus, tilting tendency while pulling is diminished.

874 

HST 

60 kg 

pulling 

5 ° 

F hands 

in N 

F L5-S1 

in kN 

Furthermore, the roller conception may be reconsidered 

with respect to easy manoeuvring and maintain good 

quality of wheeling, as enhanced friction (e.g. scruffy axle 

bearing) requires intensified force exertion for the flight 

attendants and, in consequence, yield to higher lumbar 

load. Regarding extreme flight conditions, i.e. moving 

heavy containers on a steep floor, provision of motordriven 

trolleys may be examined. 

4.3. Criticism of the methods 

The provided investigation into low-back load of flight 

attendants during moving meal-and-drink containers on an 

inclined floor comprises comprehensive measurements of 

posture and exerted forces as well as subsequent complex 

biomechanical model calculations and diverse evaluations 

with respect to lumbar overload. Nevertheless, a couple of 

critical aspects can be discussed in order to illustrate the 

limitations of the study on hand. These items of criticism 

can be attached to the focus of the study, to the category of 

applied instruments and data recording and to the 

interpretation of the results. 

Analysing the load on the lumbar spine during trolley 

handling implies that other activities remained unconsidered 


200 

200 


100 



100 

leftward + / 

rightward - 

0 

0 

0 2 4 6 8 10 0 2 4 6 8 10 

-100 

-200 

6 

5 

4 

3 

2 

1 

0 


min. disc compression max. disc compression 


-100 

-200 

right hand left hand right hand left hand 


grasp at bars 


. 

lateral shear 

0 2 4 6 8 10 

5 s 

manoeuvres resulting in extreme lumbar load 

grasp at bar 

6 

5 

4 

3 

time in s 

forward + / 

backward - 


2 


1 

lateral 

0 

0 2 

. 

4 6 

shear 

8 10 

Fig. 6. Exemplary comparison of manoeuvres resulting in the lowest (diagrams left) or the highest disc compression (diagrams right) for an identical 

experimental configuration (HST, 60 kg, pulling, 51). Bars in the headline indicate grasp positions (black squares) and bar orientation (vertical vs. 

horizontal). Upper part: action forces at both hands. Lower part: corresponding reaction forces at the lumbosacral disc. 

(cf. Schaub et al., 2007) and that other body regions or 

organs were not proved regarding potential overload. This 

approach is based on the first fact that the complaints of 

female flight attendants about excessive physical workload 

encouraged the corresponding German Institution for 

Statutory Accident Insurance and Prevention to initiate 

the study and to select the main aims (cf. Glitsch et al., 

2007). The second reason is represented by the actual 

recordings of the subjective perception of flight attendants 

via questionnaires. The respective results show the highest 

values for both complaints and physical load related to the 

lower back (cf. Schaub et al., 2007) so that focussing on 

lumbar load seems to be justified. 

Another aspect of criticism is related to the applied tools 

for obtaining data on posture, hand–forces and lumbarload 

prediction. As a first example, the CUELA measuring 

system represents a comprehensive tool for ambulatory 

recording of totally 26 postural indicators over time, four 

of which describe the sagittal flexion angles of knee and hip 

joints, on the one hand; that means lateral and medial 

rotation of the thighs remained unconsidered, on the other 

hand. Estimating rotation’s effects on trolley handling as 

performed in the laboratory experiments illustrates that the 

main direction of motion and force exertion is pointed

forward or backward. In consequence, predicted values for 

compressive force and sagittal moment at L5–S1 adequately 

reflect these predominant factors and are not considerably 

influenced by inaccuracies caused by neglected thigh rotations. 

The second example concerns the replication of the 

anatomical structures in the biomechanical model, THE 

DORTMUNDER. Regarding the skeletal modelling, standardized 

percentages for the dimensions of body segments were 

implemented (e.g. Dempster, 1955; Drillis and Contini, 1966; 

White and Panjabi, 1978), since the individual proportions of 

the subjects participating in the laboratory study were not 

obtained due to the time consuming procedures for the 

‘‘main’’ measurements on posture and action forces during 

trolley handling manoeuvres. Considering the typical anthropometry 

of flight attendants avoiding overweight, however, 

effects of body weight and, in particular, its distribution 

according to individual proportions seem negligible in 

relation to exerted forces. Further details of assumptions 

and restrictions of both tools, CUELA and THE DORTMUNDER, 

are provided in the respective descriptions (Ellegast and 

Kupfer, 2000; Ja¨ ger et al., 2001). 

Besides the features of a model, its application in the 

provided study may lead to further discussions. As 

mentioned in Section 2, THE DORTMUNDER was used 

quasi-statically so that inertial effects of body-mass 

acceleration on lumbar load were neglected. Since the 

trolleys are predominantly moved by performing consecutive 

steps, i.e. by movements of the legs, and since the 

upper-body segments show relatively slow, translational 

motions during the pushing-or-pulling periods including 

only little rotation of trunk and arm segments, the resultant 

inertial effects on lumbar load were considered negligible in 

relation to exerted forces. 

The evaluation of lumbar load is based on a sub-sample 

of 468 handling activities, although raw data on more than 

3,000 manoeuvres were obtained in the course of the 

laboratory experiments. However, inspection and verification 

of the manifold data sets for posture and hand-forces 

as well as the model calculations for complete manoeuvres, 

covering each about 200 up to 500 separate situations and 

corresponding lumbar-load predictions, represent very 

time-consuming procedures. In consequence, restriction 

on a sub-sample was necessary to keep the investigation’s 

duration in tolerably reasonable times. Even if about 

15,000 situations are after all represented in the total data 

pool, nevertheless, load evaluation for some task configurations 

is based on a small number of manoeuvres only. 

The evaluations for similar task configurations show 

analogous estimations, as the corresponding results for 

neighbouring white-to-dark coloured cells in Fig. 5 

illustrate. This may indicate that the respective data pool 

for a discussed ‘‘small-number’’ task configuration was 

representative or, at least, not misleading. 

The various trolley handling tasks were assessed with 

respect to potential lumbar overload by means of four 

criteria in total, which refer to the level and distribution of 

both disc compressive-force and sagittal-moment values for 



a certain data pool obtained for identical task conditions 

each. Comparison of corresponding share evaluations 

show that application of the moment criterion results in 

higher overload-risk categories than applying the disccompression 

criterion for some task configurations, 

whereas inverse effects were not received (cf. Fig. 5, upper 

part: dark/grey Ms cells more frequent than dark/grey Fc 

cells). This may be traced back to the different backgrounds 

of moment classification and compression-related 

recommendations. The latter criteria focus on the loadbearing 

capacity of spinal structures only, and the former 

criteria additionally include attributes of the physical 

capacity and the training status of working persons. 

Therefore, the share evaluations based on the moment 

criterion should not be disregarded in order to strive for 

appropriate protection, even if the compression criterion 

may show a minor overload risk for the same task. In total, 

the detailed evaluation approach applied in this paper 

illustrates the advantage of a stepwise procedure, starting 

with the ‘‘bottle-neck attempt’’ of focussing on skeletal 

lumbar load and expending via the supplementary inclusion 

of other physiological risk criteria. 

The previous evaluating procedures focussed on the 

effects of objective working conditions and of individuals 

execution techniques on the resulting lumbar load during 

trolley handling in order to derive biomechanically justified 

measures of work design. Preferring technical control, 

anthropometric characteristics remained therefore unconsidered. 

Even if not provided in detail here, respective 

analyses were performed with regard to the influences of 

stature, body weight and the ‘‘body mass index’’ on lumbar 

load (Sawatzki and Ja¨ ger, 2006). Roughly described, 

slightly smaller values for compressive forces and moments 

of force at the lumbosacral disc were found for persons of 

low body height or weight. The only exception is pulling of 

unladen FSTs if executed by tall or heavy subjects; then, 

these lumbar-load indicators show relatively low values. In 

these cases, however, distinct trunk inclination or kyphotic 

curvature was particularly observed for tall persons; this 

aspect may be interpreted as a result of the existing trolley 

dimensions and design, which hinder grasping at an 

adequate vertical position. 

5. Concluding remarks 

The load on the lumbar spine of flight attendants during 

pushing and pulling trolleys aboard aircraft was analysed by 

means of laboratory experiments—in order to obtain 

appropriate data on posture and exerted forces—and by 

subsequent biomechanical model calculations. Several lumbar-load 

indicators were quantified for different task conditions 

regarding handling mode and floor gradient as well as 

trolley type and mass, varying each in common ranges. 

To estimate biomechanical overload risk for the lumbar 

spine, comparison of predicted lumbar-load values with 

recommended limits provided in the literature indicates 

specific patterns regarding the four ‘‘basic tasks’’, i.e. push

876 

or pull FST or HST, respectively. Moving the small 

containers (HST) shows clear, but contradictory results 

according to the handling mode: regardless of different 

surface inclinations and trolley loadings, no lumbar overload 

risk was found for pushing, whereas exceeding the 

recommended limit was frequently established for pulling a 

HST. Pushing and pulling of the large containers (FST) 

lead to ‘‘critical’’ lumbar load in cases of superimposition 

of both considerable trolley mass and considerable floor 

gradient. However, even the tasks inducing relevant 

lumbar-overload risk can positively be modified by 

adopting appropriate postures, that means by applying 

an improved handling technique: pulling of HSTs should 

never be performed using grasp positions at the top edge in 

order to reduce the tilt tendency of a HST. For all of the 

three other basic tasks, i.e. pushing the small containers as 

well as pushing and pulling the large containers, grasping 

at the upper edge of the trolley is recommended. 

Besides individual performance characteristics, the construction 

could also be improved, for example, by reconsidering 

the current roller conception or by mounting suitable 

handgrips or bars. A matter of fundamental concern seems 

guaranteeing adequate maintenance, in particular, of the 

rollers to keep friction in reasonable range. 

References 

Al-Eisawi, K.W., Kerk, C.J., Congleton, J.J., Amendola, A.A., Jenkins, 

O.C., Gaines, W., 1999. Factors affecting minimum push and pull 

forces of manual carts. Applied Ergonomics 30, 235–245. 

Andersson, G.B.J., Örtengren, R., Nachemson, A., 1977. Intradiskal 

pressure, intraabdominal pressure and myoelectric back muscle 

activity related to posture and loading. Clinical Orthopaedics and 

Related Research 129, 156–164. 

Chaffin, D.B., 1969. Computerized biomechanical model—development 

of and use in gross body actions. Journal of Biomechanics 2, 429–441. 

Dempster, W.T., 1955. Space requirements of the seated operator. Wright 

Air Development Center, WADC Technical Report No. 55-159, Ohio. 

Drillis, W.T., Contini, R., 1966. Body segment parameters. Office 

of Vocational Rehabilitation, Department Health, Education and 

Welfare, Report No. 1163-03, New York. 

Ellegast, R.P., Kupfer, J., 2000. Portable posture and motion measuring 

system for use in ergonomic field analysis. In: Landau, K. (Ed.), 

Ergonomic Software Tools in Product and Workplace Design. Ergon, 

Stuttgart, pp. 47–54. 

Glitsch, U., Ottersbach, H.J., Ellegast, R., Hermanns, I., Feldges, W., 

Schaub, K., et al., 2004. Untersuchung der Belastung von Flugbegleiterinnen 

und Flugbegleitern beim Schieben und Ziehen von Trolleys in 

Flugzeugen. Hauptverband der gewerblichen Berufsgenossenschaften 

(HVBG) (Ed.), BIA-Report 5/2004. /http://www.hvbg.de/d/bia/pub/ 

rep/rep04/bia0504.htmlS, Sankt Augustin. 

Glitsch, U., Ottersbach, H.J., Ellegast, R., Schaub, K., Jäger, M., Franz, 

G., 2007. Physical workload of flight attendants when pushing and 

pulling trolleys aboard aircraft. International Journal of Industrial 

Ergonomics, in press, doi:10.1016/j.ergon.2007.07.004. 

Hoozemans, M.J.M., van der Beek, A.J., Frings-Dresen, M.H.W., van 

Dijk, J.H., van der Woude, L.H.V., 1998. Pushing and pulling in 

relation to musculoskeletal disorders: a review of risk factors. 

Ergonomics 41, 757–781. 

Hoozemans, M.J.M., Kuijer, P.P.F.M., Kingma, I., van Dieen, J.H., de 

Vries, W.H.K., van der Woude, L.H.V., et al., 2004. Mechanical 

loading of the low back and shoulders during pushing and pulling 

activities. Ergonomics 47, 1–18. 



Jäger, M., 2001. Belastung und Belastbarkeit der Lendenwirbelsa¨ ule im 

Berufsalltag—ein interdisziplinärer Ansatz fu¨ r eine ergonomische 

Arbeitsgestaltung. Fortschritt-Berichte VDI, Reihe 17, No. 208. 

VDI-Verlag, Du¨ sseldorf. 

Jäger, M., Luttmann, A., 1997. Assessment of low-back load during manual 

materials handling. In: Seppa¨ lä, P., Luopajärvi, T., Nyga˚rd, C.-H., Mattila, 

M. (Eds.), Musculoskeletal Disorders, Rehabilitation. Proceedings of the 

13th Triennial Congress International Ergonomics Association, vol. 4. 

Finnish Institute of Occupational Health, Helsinki, pp. 171–173. 

Jäger, M., Luttmann, A., 1999. Critical survey on the biomechanical 

criterion in the NIOSH method for the design and evaluation of 

manual lifting tasks. International Journal of Industrial Ergonomics 

23, 331–337. 

Jäger, M., Luttmann, A., Laurig, W., 1991. Lumbar load during onehanded 

bricklaying. International Journal of Industrial Ergonomics 8, 

261–277. 

Jäger, M., Luttmann, A., Göllner, R., Laurig, W., 2001. The Dortmunder—biomechanical 

model for quantification and assessment of the 

load on the lumbar spine. In: Society of Automotive Engineers (Ed.), 

SAE Digital Human Modeling Conference Proceedings (CD-Rom, 

Paper 201-01-2085, 9pp), Arlington, VA. 

Jung, M.-C., Haight, J.M., Freivalds, A., 2005. Pushing and pulling carts 

and two-wheeled hand trucks. International Journal of Industrial 


Laursen, B., Schibye, B., 2002. The effect of different surfaces on 

biomechanical loading of shoulder and lumbar spine during pushing 

and pulling of two-wheeled containers. Applied Ergonomics 33, 167–174. 

Lee, K.S., Chaffin, D.B., Herrin, G.D., Waikar, A.M., 1991. Effect of 

handle height on lower-back loading in cart pushing and pulling. 

Applied Ergonomics 22, 117–123. 

Mital, A., Nicholson, A.S., Ayoub, M.M., 1997. A Guide to Manual 

Materials Handling. Taylor & Francis, London. 

Morris, J.M., Lucas, D.B., Bresler, B., 1961. Role of the trunk in stability 

of the spine. Journal of Bone and Joint Surgery 43A, 327–351. 

Nachemson, A., 1966. The load on the lumbar disks in different positions 

of the body. Clinical Orthopaedics 45, 107–122. 

Nachemson, A., Elfström, G., 1970. Intravital dynamic pressure 

measurements in lumbar discs. Scandinavian Journal of Rehabilitation 

Medicine (Suppl. 1). 

NIOSH, National Institute for Occupational Safety and Health, 1981. 

Work Practices Guide for Manual Lifting. Department of Health and 

Human Services, Cincinnati, pp. 81–122. 

Sawatzki, K., Jäger, M., 2006. Untersuchungen zur Identifikation von 

Kriterien fu¨ r eine wirbelsäulenschonendere Handhabung von Trolleys in 

Flugzeugen. Institut fu¨ r Arbeitsphysiologie an der Universität Dortmund, 

BG fu¨ r Fahrzeughaltungen (Eds.), Dortmund, Hamburg. /http://www. 

ifado.de/forschung/biomech/Lastenhandhabung/Ergaenzungsstudie.pdfS. 

Schaub, K., Berg, K., Winter, G., Ellegast, R., Glitsch, U., Ottersbach, 

H.J., et al., 2007. Muscular capabilities and workload of flight 

attendants for pushing and pulling trolleys aboard aircraft. International 

Journal of Industrial Ergonomics, this issue, doi:10.1016/ 

j.ergon.2007.07.002. 

Schibye, B., Søgaard, K., Martinsen, D., Klausen, K., 2001. Mechanical 

load on the low-back and shoulders during pushing and pulling of twowheeled 

waste containers compared with lifting and carrying of bags 

and bins. Clinical Biomechanics 16, 549–559. 

Tichauer, E.R., 1978. The Biomechanical Basis of Ergonomics—Anatomy 

Applied to the Design of Work Situations. Wiley, New York. 

Waters, Th.R., Putz-Anderson, V., Garg, A., Fine, L.J., 1993. Revised 

NIOSH equation for the design and evaluation of manual lifting tasks. 


White, A.A., Panjabi, M.M., 1978. Clinical Biomechanics of the Spine. 

Lippincott, Philadelphia. 

Wilke, H.-J., Neef, P., Caimi, M., Hoogland, T., Claes, L.E., 1999. New in 

vivo measurements of pressures in the intervertebral disc in daily life. 

Spine 24, 755–762. 

Winkel, J., 1983. On the manual handling of wide-body carts used by 

cabin attendants in civil aircraft. Applied Ergonomics 14, 162–168.

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