Does reduced hamstring flexibility affect trunk and pelvic movement strategies
during manual handling?
Rodrigo Luiz Carregaro, Helenice Jane Cote Gil Coury*
Department of Physical Therapy, Laboratory of Preventive Physical Therapy and Ergonomics, Federal University of Sa ˜o Carlos (UFSCar), Via Washington Luiz, Km 235,
CEP 13565-905, Sa ˜o Carlos, SP, Brazil
a r t i c l e i n f o
Received 29 May 2007
Received in revised form 9 April 2008
Accepted 14 May 2008
Available online 21 July 2008
Low back pain
a b s t r a c t
Objective: To evaluate the influence of reduced hamstring flexibility on trunk and pelvic movement
strategies adopted by healthy males during manual handling tasks.
Methods: Seventeen subjects performed a sagittally symmetrical handling task involving a 15 kg box, and
hamstring flexibility was measured by means of the Straight Leg Raise Test. The task was filmed with
a 2D acquisition system at a sampling rate of 50 frames/s. The images were digitized and a MatLab?
routine was implemented to analyze the trunk and pelvis movement patterns. Kinematic data from trunk
movements were plotted against the data from pelvic movements in order to provide coordination
Results: Subjects with reduced flexibility presented higher trunk movement amplitudes and a restriction
on pelvis movements during handling tasks. Movement coordination was also influenced by the reduced
Conclusion: The results suggest that reduced hamstring flexibility is related to increased trunk angles,
which can overload the spine during manual materials handling.
Relevance to industry: Hamstring shortness can influence pelvic dynamics and, consequently, affects
trunk movements adopted by subjects during occupational activities. As movement restrictions can
reduce the capacity to obtain appropriate postural responses, this should be accounted for in order to
provide better comprehension on how to prevent low back injuries in the occupational setting.
? 2008 Elsevier B.V. All rights reserved.
The multifactorial nature of low back pain has long been rec-
ognized (Burdorf and Sorock, 1997; Granata and Marras, 1999;
Manchikanti, 2000; Marras, 2000; Leboeuf-Yde, 2004). Different
work factors have been associated with the genesis of occupational
disorders, such as heavy work (Marras, 2000), manual materials
handling (Kuiper et al.,1999), lack of physical activity (Manchikanti,
2000; Stevenson et al., 2001), inadequate postures (Burdorf and
Sorock, 1997), changes in movement coordination (Granata and
Sanford, 2000) and specific personal characteristics such as ham-
string flexibility (Feldman et al., 2001; Sjo ¨lie, 2004).
Measurements of hamstring flexibility were used by Grenier
et al. (2003) for evaluating histories of low back pain among in-
dustrial workers. These authors suggested indicators for the
relationship between reduced flexibility and the development of
low back pain. Hamstring shortness was also associated with low
back pain according to Feldman et al. (2001) and with poor hip
mobility in adolescents according to Sjo ¨lie (2004).
According to Norris (2000), changes in muscle length occur in
a non-uniform way throughout the body segments. Although
simple, a useful description of this mechanisms is that stabilizer
muscles, or postural muscles, tend to sag, whereas mobilizer
muscles, or task muscles, tend to tighten. Thus, the hamstrings, an
important mobilizer of the pelvis, can become tightened com-
monly. To compensate this, the adjacent segment (spine) presents
relative higher flexibility (White and Sahrmann, 1994). Thus, if the
hamstrings are shortened, the pelvic tilting is limited and the more
lax spinal tissues will be stressed (Norris, 2000). Also, as the
hamstrings can alter the force transmission between the lower
limbs and trunk, and sustain excessive erector spine electromyo-
graphic activity during dynamic activities (Kroll and Raya, 1997),
the hamstring shortness will affect lumbar and hip functions
(Hamill and Knutzen, 1995; Shin et al., 2004). These presumptions
lead to the hypothesis that hamstring shortness can affect trunk
and pelvic dynamics during manual material handling.
Considering that lifting/lowering activities impose extra loads
upon the spine, the comprehension of the movement strategies
* Corresponding author. Tel.: þ55 16 3351 8634.
E-mail address: firstname.lastname@example.org (H.J.C. Gil Coury).
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International Journal of Industrial Ergonomics 39 (2009) 115–120
adopted by workers presenting hamstring shortness can provide
knowledge for improving rehabilitationprograms and safer manual
techniques. Naturally, it is important to recognize that, despite
decades of investigations, the prevention of occupational low back
pain still remains a challenge with exercise programs being only
a small part of it. Even so, the understanding of muscle character-
istics and movement strategies adopted during handling can help
to improve preventive and rehabilitation programs for risk exposed
Although several studies have compared healthy subjects and
those with low back pain symptoms, with the aim of discriminating
their dynamic characteristics during free trunk movements (Kang
et al., 1995; McGregor et al., 1995; Lee and Wong, 2002; Wong and
Lee, 2004) and during manual materials handling (Ferguson et al.,
2004; Wrigley et al., 2005), no study with the aim of understanding
the influence of reduced hamstring flexibility on the movement
strategies adopted by subjects during manual handling activities
Thus, the purpose of this study was to evaluate the influence of
hamstring flexibility on the trunk and pelvic movement strategies
adopted by male workers while lowering and lifting a box. It is
hypothesized that the hamstring muscles exert an influence on
pelvic and trunk dynamics while performing manual handling ac-
tivities. In the present study, Stergiou’s definition of ‘‘strategy’’ was
adopted as follows: a neuromusculoskeletal solution adopted for
performing a motor task, which results in a specific movement
pattern (Stergiou, 2004).
Seventeen healthy male were recruited for the study. They were
manual handling workers in the stocking sectors of local super-
markets, with at least six months of occupational experience.
Subjects constituted a convenience sample as there was the need
for controlling the subjects’ height and previous experience on
handling. The inclusion criteria were (1) age between 18 and 35
years and (2) height between 1.65 and 1.75 m. Subjects were ex-
cluded if they presented (1) equilibrium disorders (positive Rom-
berg test), (2) histories of orthopedic problems, such as fractures,
surgery and pain in the low back and lower limbs over the past six
months, (3) postural asymmetries and (4) diagnosis of in-
tervertebral disk herniation.
Personal data were collected from the subjects. The selected
individuals were familiarized with the experimental setting, in-
formed about the objectives and procedures of the study, and
signed an informed consent. The project was approved by the Re-
search Ethics Committee of the University (Proc. No. 059/04).
Hamstring flexibility was measured in all subjects by means of
the Straight Leg Raise Test, based on Gajdosik et al. (1994). This test
provides an indirect measurement of hamstring shortness, based
on hip range of motion (Gajdosik et al.,1993) and was considered to
be avalidclinical measurement for this purpose (Gajdosik,2001). In
this test, the angle of the leg was measured in relation to a hori-
zontal line. Subjects presenting angles greater than or equal to 65?
were classified as having normal flexibility, while individuals pre-
senting angles less than 65?were classified as having reduced
flexibility. In this study, flexibility was accepted as the capacity to
move a joint through its available range of motion (ROM), without
producing excessive myotendinous stress (Alter, 1996). Details
about the procedures and measurement reliability can be found
elsewhere (Carregaro et al., 2007). After this test, the individuals
were divided into two groups: (1) reduced flexibility: 10 subjects
with mean age of 23.3?2.9 years, mean height of 1.68?0.03 m,
mean weight of 64.5?10.4 kg and mean leg elevation of 55?5?;
and (2) normal flexibility: seven subjects with mean age of
25.4? 4.5 years, mean height of 1.69?0.04 m, mean weight of
66.8?6.8 kg and mean leg elevation of 73?7?. Both age and time
of experience in handling were not statistically different between
A JVC digital camera (GR-DV 1800) was used to record the
manualmaterials handlingat an acquisition rateof 50 frames/s. The
camera was placed perpendicularly to the subjects’ sagittal plane
(on the right side), at a distance of 3.8 m. Reflective anatomical
landmarks were attached to the skin at the following bone refer-
ences: seventh vertebra spinous process (C7), anteriorsuperior iliac
spine (ASIS) and greater trochanter (GT). From the anatomical
landmarks, the following angles were measured: trunk flexion (To:
the angle between the line joining C7 to ASIS and the extrapolation
of the line joining ASIS to GT) and pelvis inclination (Po: the angle
between the line joining ASIS to GT and the horizontal line), based
on Whistance et al. (1995). The shelf surfaces were fixed, and
reproduced the mean heights of fixed shelves used in the stocking
sectors analyzed (see Fig. 1).
Sagittally symmetrical manual materials handling between
different heights was simulated. The lowering task was from an
intermediate surface (height of 100 cm) to a lower surface (height
of 59 cm). The lifting task was from the lower surface back to the
Fig. 1. Manual handling. Angles of trunk flexion (To) and pelvic inclination (Po). Han-
dling surfaces: intermediate (Int: height of 100 cm) and lower (Low: height of 59 cm)
(C7: seventh spinal process, ASIS: anterior superior iliac spine and GT: greater
R.L. Carregaro, H.J.C. Gil Coury / International Journal of Industrial Ergonomics 39 (2009) 115–120116
intermediate surface (Fig. 1). Each handling task was performed
once, with a 15 kg box (300?300?180 mm). The handling
sequence was randomized between the subjects.
The subjects were instructed about the handling sequence and
were told to perform the task in the way that they chose to do it.
However, they were also instructed to avoid excessive trunk axial
rotation, as Kingma et al. (1998) affirms that controlling axial ro-
tation is essential in 2D analysis to minimize bias. No restrictions
were placed on lower limb movements, and no guidance was given.
2.4. Manual handling analysis
The beginning and end of the task were determined visually. For
this, the images at the instants when the subjects first touched and
finally released the box were selected, respectively. The manual
handling images were edited and digitized by means of the Ariel-
Apas?software, and the resulting kinematic data were analyzed
using a MatLab?(version 6.5, MathWorks Inc., Natick, MA, USA)
routine that was specially designed for this study. The reference
position for the kinematic data was established as the posture at
the instant when the subjects got hold of the box on the in-
termediate surface. From the reference position, the trunk and pelvic
movements were conventionalized as flexion (?) and extension (þ).
The raw data were digitally filtered with a second-order Butterworth
filter, with a cutoff frequency of 4 Hz, which was determined by re-
sidual analysis (Winter, 1990). The data were interpolated to 101
points and the time base was normalized (% of total time) in order to
provide comparable movement patterns between groups.
2.5. Trunk and pelvis coordination analysis
Kinematic data from trunk movements were plotted against the
data from pelvic movements, thus producing angle–angle plots
(Lee and Wong, 2002). This analysis was applied in order to de-
scribe the relationship between trunk and pelvis, and to provide
a comparison of the movement behavior between the flexibility
groups during the lowering and lifting tasks.
2.6. Postural adjustment analysis
Significant changes in angular amplitude of the trunk and pelvis
during a period of time were defined as the ‘‘postural adjustment’’
adopted by the subjects while performing the manual handling
tasks. After the digitalization, images were converted into move-
ment patterns. Considering the real time duration of the task, the
kinematic data were windowed in consecutive windows of 25
points (0.25 s) in order to identify the first postural adjustment.
Time was normalized in % of real time after the windowed pro-
cedure. Then, the mean and standard deviation of each window
were calculated. For flexion movements, postural adjustments
were deemed to occur when the mean amplitude of a current
window was lower than the mean value minus 1.96 standard de-
viations of the previous window and higher than the mean value of
the subsequent window. For extension movements, postural
adjustments were deemed to occur when the mean value of a cur-
rent window was higher than the mean value plus 1.96 standard
deviations of the previous window and lower than the mean value
of the subsequent window (Noe ´, 2006).
2.7. Statistical analysis
The Statistical Package for the Social Sciences (SPSS) version 10.0
was used for the statistical analysis. Data that did not present any
normality assumptions, as found by the Shapiro–Wilks test, were
logarithmically transformed in order to be able to use inferential
statistics. All data were analyzed in relation to their means and
standard deviations, and the significance level was set at 5%
(P<0.05). An independent t-test was used to identify significant
differences between the reduced and normal flexibilitygroups with
regard to: (1) trunk and pelvic range of motion at the moment
when the box was deposited, (2) total range of movement adopted
during the manual handling tasks and (3) the instant when the
postural adjustment occurred.
Table 1 shows the range of movement presented during box
lowering and lifting. No significant differences between the groups
were identified during the lowering task, for either the trunk
(P¼0.13) or the pelvic (P¼0.28) amplitudes. Also, during this task,
the subjects with reduced flexibility (RF) presented lower pelvic
amplitudes and higher trunk amplitudes (mean differences of 9.7?
and 11.9?, respectively) than did the normal flexibility (NF) group.
During the lifting task, RF subjects presented significantly higher
trunk amplitudes (P¼0.006). There was no significant difference in
pelvic amplitudes between the groups during the lifting task (mean
difference of 7.5?, P¼0.2). High variability was identified for the
different conditions, particularly for the pelvis angles.
There were no significant differences between the groups dur-
ing the lowering task (P¼0.3 and 0.1, respectively, for trunk and
pelvic adjustments; Fig. 2A and B) and during the lifting task
(P¼0.5 and 0.9; Fig. 2C and D). Nonetheless, it could be seen that
the subjects with reduced flexibility adjusted their pelvis position
earlier during the lowering task than did the subjects with normal
flexibility (Fig. 2A and B). Both groups adjusted first the trunk and
then the pelvis, when lowering the load. The NF group presented
a longer time interval between making the trunk and pelvic ad-
justments than that observed for the RF group. The differences in
the lifting task were not pronounced.
In a general manner, Fig. 2 visually confirms the mean data
presented in Table 1, namely that subjects with reduced flexibility
presented higher trunk amplitudes during lowering and lifting
tasks. Also, subjects with reduced flexibility tended to already
adopt a flexed posture with some pelvic extension at the beginning
of the lowering (between 20 and 40%) and to maintain this pattern
until 80–90% of the task had been completed. In general, higher
variability in trunk movements was shown by the RF group than by
the NF group, for both the lowering and the lifting task. The op-
posite tendency was shown by the RF group for pelvis inclination,
particularly for the lowering task.
Fig. 3 visually presents the mean trunk flexion values plotted
against pelvic inclination for both groups of subjects. It can be seen
that the RF group tended to adopt retroverted pelvic amplitudes
and higher trunk flexion amplitudes. On the other hand, the sub-
jects with normal flexibility tended to show higher anteroverted
pelvic amplitudes and lower trunk amplitudes during the handling
tasks. Furthermore, the reduced flexibility group presented a pelvic
range of movement of approximately 7?(see x axis – vales ranged
from ?1?to 6?), while the subjects with normal flexibility had
a range of movement of 13.5?(see x axis – values ranged from ?10?
Total range of motion (maximum range minus minimum range) by each group
during lowering and lifting tasks (mean?standard deviation, values in degrees).
Values are in degrees; RF: reduced flexibility; NF: normal flexibility; * significant
difference between groups (P<0.05).
R.L. Carregaro, H.J.C. Gil Coury / International Journal of Industrial Ergonomics 39 (2009) 115–120117
The subjects with reduced flexibility (RF) presented higher
trunk amplitudes during the handling tasks, and this could indicate
that they were compensating for their pelvic restriction. Other
biomechanical, kinesiological and individual factors can also affect
pelvic restriction, however, other studies (Feldman et al., 2001;
Grenier et al., 2003; Sjo ¨lie, 2004) have also raised the hypothesis
that restriction of pelvic movement is related to hamstring short-
ness and could be considered to be predisposing factor for low back
Fig. 3. Mean trunk flexion values plotted against pelvic inclination for the normal and reduced flexibility groups during lowering and lifting tasks (arrows show the movement
direction in relation to the beginning and end of the task). RF: reduced flexibility group and NF: normal flexibility group.
Fig. 2. Movement patterns for trunk (A and C) and pelvis (B and D) during box lowering (A and B) and lifting (C and D) for groups presenting normal flexibility (NF) and reduced
flexibility (RF). Gray and black vertical lines represent the instants when the subjects adopted the first postural adjustment. Curve values in degrees; SD: standard deviation; ROM:
range of motion.
R.L. Carregaro, H.J.C. Gil Coury / International Journal of Industrial Ergonomics 39 (2009) 115–120118
pain. The present findings from the RF group also showed that they
had lower variabilityand loweramplitudes for their pelvicpatterns,
which corroborate the possible relation between pelvic restriction
and hamstring shortness. Despite that, the causality between these
variables has not been addressed in the present study.
Anteroversion of the pelvis presented by the NF group during
the handling tasks seems to contribute for the maintenance of the
physiological lumbar lordosis during handling. On the contrary, the
subjects with reduced flexibility presented a retroverted pattern.
This retroversion might be associated with some risk factors, such
as limitations on lumbar spine range of motion and its rectification.
In fact, it has been recognized that, during trunk flexion, the rec-
tified position of the lumbar spine presents larger shear forces
(Potvin et al., 1991) and larger contributions from passive compo-
nents (Arjmand and Shirazi-Adl, 2005).
Descriptive data presented on the relation between trunk and
pelvic movement patterns showed that the trunk and pelvic ad-
justments during the handling tasks occurred earlier in the RF
groupthan in the NF group.These findings might suggest an altered
movement pattern. Esola et al. (1996), analyzing subjects with
a history of low back pain, have observed that subjects tended to
use earlier and higher amplitudes of lumbar spine movement
during forward bending tasks. They also suggested that this earlier
lumbar motion had important clinical implications, as it placed
tensile stress on posterior elements of the spine. In fact, such im-
plications are important, as a poor stability of the spine resulting
from strained ligaments could increase the musculoskeletal load
(Sjo ¨lie and Ljunggren, 2001). The earlier lumbar adjustments
identified by Esola et al. (1996) and in the present study may be
relatedtosimilar movementstrategies,however, lowbackpainwas
not investigated in the present study.
Even considering the fact that the manual handling performed
in this study was sagittally symmetrical, the use of a 2D acquisition
system imposed a technical difficulty in acquiring kinematic data
on the lower limbs. In order to keep the simulated handling more
realistic, no lower limb restrictions were imposed on the partici-
pants. As a consequence, it was not possible to evaluate the in-
fluence of hamstring flexibility on knee dynamics. Thus, we suggest
that future studies evaluating the influence of hamstring flexibility
during manual materials handling should also record the knee
joints and use a 3D acquisition system for this purpose.
Shin et al. (2004) presented interesting results regarding the
influence of flexibility on different trunk positions. It seems that
hamstring flexibility had effects on the electromyographic activity
of the trunk muscles and altered the spine flexion–relaxation re-
sponse. In this respect, future studies should consider evaluating
hamstring electromyography in order to determine possible in-
teractions between reduced flexibility and muscle activity during
manual materials handling. In addition to a kinematic 3D analysis,
these measurements could help to elucidate the influence of ham-
string flexibility on spine overload during occupational activities.
According to Sedwick and Gormley (1998), it is important to
recognize the presence of variability in tasks and workers’ in-
dividuality. In this respect, the current study reinforces the idea
that training for manual materials handling operations should not
be prescribed in a standard manner, but instead, should teach
subjects to consider their individual limitations and to identify
risky situations. It is also worth to mention the need for the iden-
tification of several other possible risks occurring in the occupa-
tional setting for more effective prevention of low back disorders.
Furthermore, the biopsychosocial model of illness, applied in the
context of low back pain (Weiner, 2008), should be taken into
account for a more comprehensive approach to the issue.
Evaluation of physical characteristics such as hamstring flexi-
bility enables an understanding of alternative movement strategies
adopted by healthy males during manual handling tasks, in
response to reduced flexibility. In this sense, the limitation of ajoint
(for instance, a restrained hip in consequence of hamstring short-
ness) could reduce the capacity to obtain an appropriate postural
response during dynamic occupational activities. The present
results have indicated that lower hamstring flexibility could in-
fluence pelvic dynamics and, consequently, alter the movement
patterns and trunk amplitudes adopted by subjects during occu-
pational handling tasks.
Subjects with reduced hamstring flexibility presented higher
trunk amplitudes during handling tasks than did subjects with
normal flexibility. The results also suggest that reduced hamstring
and ligament overload at the spine during manual handling tasks.
This study was supported by CAPES and CNPq. The authors
thank Dr. Jose ´ Angelo Barela (UNESP, SP) and Dr. Ana Maria Barela
for allowing the use of sources from their lab for the image analysis
presented in this study.
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