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

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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
ARTICLE IN PRESS
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