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An empirical studyof preferred settings
for lumbar support on
adjustable office chairs
NICK COLEMAN , BRYNLEY P. HULL & GLENAELLITT
Published online: 10 Nov 2010.

To cite this article: NICK COLEMAN , BRYNLEY P. HULL & GLENA ELLITT (1998)
An empirical study of preferred settings for lumbar support on adjustable officechairs, Ergonomics, 41:4, 401-419, DOI: 10.1080/001401398186900
To link to this article: http://dx.doi.org/10.1080/001401398186900

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E RGO N OM ICS , 1998, VOL . 41, NO . 4, 401 ± 419

An empirical study of preferred settings for lumbar support on
adjustable o ce chairs
N ICK C O LEM AN ² *, B RY N LEY P. H U LL ³ and G LENA E L LITT ²² Human Factors and Ergonomics Unit and ³ Epidemiology Unit, Worksafe
Australia, National Occupational Health and Safety Commission, GPO Box 58,
Sydney, NSW 2001, Australia

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Keywords: Lumbar support; Postural comfort; O ce chairs.
The preferred settings for lumbar support height and depth of 43 male and 80
female o ce workers were investigated. All subjects were equipped with identicalmodern o ce chairs with foam-padded backrests adjustable in both height anddepth. Measurements of lumbar support settings were recorded in the workplace,outside of working hours, on four diŒerent occasions, over a 5 week period.
Preferred lumbar support height and depth settings extended to both extremes of
the adjustment range. The mean preferred height setting was 190 mm above thecompressed seat surface. The mean depth setting (horizontal distance from frontof seat to lumbar support point) was 387 mm. A regression model examining theeŒects of standing height, Body Mass Index (BMI) and gender on mean preferred
lumbar support height showed a signi® cant relationship between preferred heightand BM I. Higher lumbar supports were chosen by subjects with greater BMIs.
Gender and standing height were not associated with preferred lumbar support
height settings. Preferred lumbar support depth was not signi® cantly associatedwith standing height, gender or BM I. Older subjects were more likely to readjust
their lumbar support from a disrupted position than younger subjects, indicatingthat older users are more sensitive to the position of their lumbar support.
Subjects who reported recent back pain or discomfort that they believed to be
associated with their chair or o ce work were found to set their lumbar support
signi® cantly closer to the front of the seat, probably to ensure greater support for
their back. Based on the evidence that a high proportion of users do makeadjustments to the height and depth of their lumbar support, and the ® nding thatdiŒerent groups of users, with diŒerent physical characteristics, adjust theposition of their lumbar support in distinct and predictable ways, the researchersconclude that o ce chairs with traditional padded ® xed-height lumbar supports
are unlikely to provide a comfortable or appropriate seat for the wide range ofpotential users.

1. Introduction
W hile there is wide agreem ent am ong experts that proper lumbar support is one of
the fundam ental requirements of an o ce chair, the most appropriate location for alumbar support has not been established (Andersson et al. 1979 , Stevenson 1991 ,M cDowell and Straker 1993 ) and the ergonom ics literature and standards are a mazeof con¯ icting recom mendations and requirements (Pheasant 1990). Some researchers(Keegan and Nebraska 1953, Keegan 1962 , Branton 1966 ) recomm end placem ent of
the support over the lower lumbar region, other research indicates that a higher
support is preferable (Sauter and Arndt 1984 , Eklund and Corlett 1987). Floyd and*Author for correspondence.
0014± 0139 / 98 $12 × 00

1998 T aylor & Francis L td

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402

N. Colem an et al.

Roberts (1958) suggest that a lumbar support is probably best positioned within thelimits of the second to the ® fth lumbar vertebrae (L2 to L5). U nfortunately, theanthropometric data for these landm arks are inadequate (Pheasant 1990 ) and very
few studies provide designers of o ce chairs with useful and reliable dim ensions forhow high a lumbar support should be above the seat. The height above the seat of
the foremost point of the lumbar support area, an d whether it needs to be adjustable,
is a m atter of contention am ong chair designers (Stevenson 1991).
The uncertainty about the optimum position, the lack of anthropometric data forthe relevant landmarks (Pheasant 1990), variation in sedentary work tasks (Corlett
1989), and the observation that diŒerent people will select diŒerent heights when
adjustm ent is availa ble and they have been trained to use it (Stevenson 1991), have led
to ergonomists generally favouring adjustable lumbar supports (Burandt andGrandjean 1963, Branton 1984 , Zacharkow 1988 , Pheasant 1990 , Andersson et al.
1991, Cha n et al. 1991, Stevenson 1991). However, the uncertainty about the
optimum position and the lack of direct research addressing lumbar support heightadjustability have provided standards setting organizations around the world with noclear justi® cation to exclude o ce chairs with ® xed height lumbar supports.
Consequently, the draft CEN Standard (CEN 1994 , pr EN 1335 ) and the AustralianStandard for the design of height adjustable swivel chairs (Standards Australia 1997 )continue to provide for o ce chairs with either ® xed or adjustable height lumbar
supports.
The present study investigates user preferences for lum bar support and addresses
some of the issues associated with lumbar support height, adjustability and user
comfort.
The speci® c aims of this study were:(1) to investigate the relationships between preferred position of lum bar supportand stature, gender, body mass index, training in o ce ergonomics and backpain prevalence;(2) to investigate whether o ce workers make use of lumbar support
adjustment facilities; and(3) to determine preferred settings for the height and depth of lum bar support
on which to base recomm endations for furniture manufacturers and theStandards Association of Australia.
2. M ethods
2.1. Subjects
The subjects in the study were 123 governm ent o ce workers employed by theAustralian National Occupational H ealth and Safety Commission (NOH SC ). Of the
123 subjects, 80 were female and 43 were m ale. Subjects ranged from senior
executives to junior administrative staŒ. The physical characteristics of subjects weresimilar to what would be expected of the Australian white collar workforce (table 1).
2.2. Chairs and tasks
All subjects were equipped with identical o ce chairs. The chairs had an appropriate
design and shape of lumbar support and the full range of seat and backrest
adjustability recomm ended by W orksafe Australia (1991). All subjects had their own
PC and during their working day mixed screen-based tasks with more traditionalo ce work.

Preferred chair settings for lumbar support
Table 1.

Age
HeightWeightDownloaded by [University of York] at 11:03 08 October 2014

BM I

403

Subject characteristics.

Males (n = 43)

Fem ales (n = 80)

All subjects (n = 123)

Mean = 36 × 8 years
Range: 19 ± 64 years
Mean = 1760 mm
r = 58 mm
Mean = 80 × 7 kg
r = 14 × 2 kg
Mean = 25 × 89
r = 3× 99

Mean = 36 × 6 years
Range: 20 ± 60 years
Mean = 1640 mm
r = 73 mm
Mean = 67 × 3 kg
r = 14× 4 kg
Mean = 25 × 16
r = 5 × 34

Mean = 36 × 7 years
Range: 19 ± 64 years
Mean = 1682 mm
r = 91 mm
Mean = 72 × 0 kg
r = 15 × 7 kg
Mean = 25 × 42
r = 4 × 91

2.3. Experimental design
The ® rst stage of the study involved systematic measurement of the current settings
for lumbar support height and depth on all standard chairs. This measurement set isreferred to as T1 (for `Test 1’ ). M easurem ents were recorded outside working hours
without prior explanation given to staŒ. Chairs were coded and labelledappropriately and chair locations were marked on ¯ oorplans.
Imm ediately following the ® rst set of measurements, all staŒ received a letter(placed on their chair) inviting them to take part in the study by making appropriate
adjustm ents to their backrests. The letter asked staŒto read the two pages shown in® gure 1 and ensure that their lumbar support was set to a comfortable position. Somegeneral information on VDU workstation set-up was also provided. The letter
informed staŒhow to make the adjustments and explained why, in the interests of
their heath, they should do so. They were asked to tick a box on a label stuck to theback of their chair once they were satis® ed that the position of their lumbar support
was appropriate. They were also asked to tick a box indicating whether they were thesole user of the chair. This, in addition to the ¯ oorplans, enabled the identi® cation of
those chairs that were used prim arily by one person.
Three days after receiving the letter and after receiving a reminder on thethird day, measurements of lumbar support height and depth were repeated on all
chairs to determine the changes that had been made (T2). This provided the ® rst
set of preferred settings for lumbar support height and depth. Having made themeasurements the lumbar support of each chair was adjusted to its lowest andmost forward position (the `disrupted’ position), which was considered to be an
awkward setting for the majority of users and therefore encouraging readjustment. In a few cases, subjects had chosen the lowest most forward position of thebackrest as their preferred setting. In these cases, the backrest was set to thehighest most forward position. A note was ® xed to the chairs thanking staŒ fortheir co-operation and advising them that they might need to readjust their
lumbar support following the m easurements made by the researchers. Four or ® ve
days later the measurem ents were repeated a third time (T3), providing a second
set of data for preferred settings.
Subjects’ height and body mass were measured at their workstations using
portable scales and a stadiometer. Their age and gender were recorded and theirbody mass index was calculated. Subjects were also asked a few short questions
regarding their history of back pain and any current symptoms, their knowledge anduse of chair adjustment features, and whether they had had training in o ceergonom ics.

Figure 1.

Photo-reduced pages of adjustment information supplied to subjects as part of the initial letter.

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404
N. Colem an et al.

Preferred chair settings for lumbar support

405

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A fourth set of measurements (T4) was obtained for all chairs 4 weeks later
providing a third set of data for preferred settings. Data were analysed using the SAScomputer programme (SAS Institute 1987).
2.4. M easurement techniques
Figure 2 shows an approximate pro® le of the chairs used in the study. The backrests
were small and designed only to provide lumbar support. The lum bar support point
was taken to be in line with the pivotal centre of the backrest. This corresponded(appropriately) with the most prominent point of the lumbar support area. Lumbar
support height and lumbar support depth were measured with the device shown on
the chair (illustrated m ore clearly in ® gure 3). Lumbar support height was taken as
the vertical distance from the seat surface (underside of the wooden base) to thelumbar support point. Lumbar support depth was de® ned as the horizontal distance,on the centreline of the seat’ s width, from the front of the seat to the lum bar support

Figure 2.

Approximate pro® le of chairs used in the study. The purpose-built measuring
device is shown in place on the chair.

N. Colem an et al.

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Figure 3.

Photograph of chair and standard measuring equipment.

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Preferred chair settings for lumbar support407

point. For speed, standardization, and ease of m easurement, the lum bar support
point on each chair was located by hooking a metal strip (`A’ ) over the backrest of
the chair. The strip was shaped to follow the lumbar curve of the chairs and had asmall hole drilled at the lumbar support point. The needle (`B’ ) of the verticallymounted anthropometer was raised to the height of the hole and the whole device
was slid over the seat surface until the point of the needle just touched the fabric of
the backrest through the hole in the m etal strip. The lumbar support height was readoŒthe counter on the anthropom eter. W ith the needle of the anthropometer still inplace, the T-bar (`C’ ) was moved along a groove in the wooden base until it came incontact with the front of the seat. The position of the T-bar on a ruler ® xed to theupper surface of the wooden base indicated the lumbar support depth. Test
measurements showed that lumbar support height, lumbar support depth and seatheight were repeatable 6 5m m.
Lumbar support heights were measured without allowing for cushion compression. Ten chairs were randomly chosen from the test sample and lumbar support
height was measured under com pression using the standard set of dummy buttocks
described in BS5940 : part 1 (British Standards Institution 1980). M ean cushion
compression values were determined for use when interpreting results.
The chairs used in the study had some de¯ exion in the backrest column so thatwhen users pushed back against the backrest the eŒective lum bar support depth
increased. This movement varied depending on such factors as the age and conditionof the chair; the upper body weight of the user, the user’ s sitting posture, and theangular position of the backrest. Standard measurement techniques are not available
for the m easurement of increased backrest rake under compression. For the
purposes of this study, however, observations of sitting behaviours and backrest
movements for ten subjects on ten diŒerent chairs were used to determine anapproxim ate range for increased lum bar support depth under compression.
3. Results
Of approximately 250 employees at NOHSC, 203 were equipped with the standard
study chair. All 203 chairs were originally measured and labelled (T1). After 3 ± 4
working days (T2), 123 employees had chosen to participate in the study and hadticked the box to indicate that their backrest was set to a comfortable position.

Table 2.

Measured lumbar support height and depth settings. Values in bold type provide a
better idea of the settings actually used by subjects.

Mean height
Minimum setting
Maximum setting
Mean height (allowing for cushion
compression during use)
Mean depth
Minimum setting
Maximum setting
Mean depth (allowing for increased
backrest rake and cushion
compression during use)

T1 (mm)T2 (mm)T3 (mm)T4 (mm)160 × 38
110
231
194

161 × 77
110
225
196

149 × 61
112
221
184

150 × 50
112
231
185

360 × 72
312
487
391

360 × 14
313
479
390

350 × 06
302
459
380

353 × 24
314
458
383

N. Colem an et al.

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M easurem ent set T3 showed that 1 week after the lumbar supports were set to themost forward and lowest or highest position, both the depth and height of thelumbar support had been readjusted on only 43% of the chairs, the depth alone had
been readjusted on 15% of the chairs, and the height alone had been readjusted on
7% of the chairs. A total of 35% of lumbar supports had not been adjusted andremained in the disrupted position. Four weeks later, m easurement set T4 showedthat 23% of the chairs still remained unadjusted. Of the 65% of chairs that had been
readjusted by T3, 53% had been subject to further readjustment.
Table 2 shows the measured lumbar support height and depth settings for eachmeasurement set. The bold values for lum bar support height include an additional 34
mm for cushion compression. The mean value of 34 mm was partly due to com pressionof the seat cushion, an d partly due to the wooden base of the measuring device
spanning dips in the seat pan where the buttocks would normally sit. The bold values
for lum bar support depth include an additional 30 mm for increased backrest rake andcushion com pression during use. This provides a better idea of the m ean depth actuallyused by subjects. M easurem ents showed that, when in use, the backrest column

Figure 4.

Distribution of preferred lumbar support height settings.

Figure 5.

Distribution of preferred lumbar support depth settings.

Preferred chair settings for lumbar support

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a

b

c

Figure 6.

Reported frequency of: (a) seat height adjustments; (b) backrest heightadjustments; (c) backrest depth adjustments.

409

410

N. Colem an et al.

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reclined an average of 23 mm (values ranged from 15 to 42 mm ). An extra 7 mm has
been added to the 23 mm to allow for com pression of the lumbar support cushioning.
3.1. M ean settings
The m easurement sets T2, T3 and T4 represent three separate measures of preferredsettings for lumbar support. However, since T3 and T4 were not independent (nointervention between them) they cannot both be included in the calculation of mean
preferred settings. A high proportion of subjects failed to readjust their backrest fromthe disrupted position by T3. This test was performed 4 ± 5 working days after lumbar
supports were moved to the disrupted position. Since they were not m onitored,
holidays, sick leave and external work activities might explain a signi® cant proportionof those who failed to readjust. M easurem ents recorded during T2 provide data basedon informed stated preferences, and measurements recorded during T4 provide
empirical data on the lumbar support settings that subjects used for 4 weeks (oradjusted to in that tim e). Therefore, measurement sets T2 and T4 were taken as themost reliable estimates of mean preferred lumbar support settings.
R [( T 2 1 T4 ) 2 ]Derived from data sets T2 and T4 () the mean preferred lumbar supportnheight setting of the experimental population was calculated to be 190 mm above thecom pressed seat surface. The mean preferred lumbar support depth, including 30 mm
for increased backrest rake and cushion compression during use, was calculated to be
387 mm. Figures 4 and 5 show distributions of the m ean preferred lumbar support
height and depth settings of subjects. For both lumbar support height and depth, thefull range of availa ble adjustment was used.
3.2. Anthropometric survey and questionnair e
A total of 97% of subjects reported knowing how to adjust the height of their seatprior to receiving the original letter (shown in ® gu re 1). Seventy-six per cent said thatthey knew how to adjust the height of their backrest and 76% said that they knew
how to adjust the seat / backrest depth. Of the subjects who reported having had
previous training in chair adjustment, 100% knew how to adjust their seat height,
85% knew how to adjust the height of their backrest and 85% knew how to adjust
the backrest angle (`lum bar support depth’ ) prior to receiving the letter.
Figures 6a ± c show reported data on frequency of chair adjustment prior to theresearch. The charts distinguish between those subjects who said that they had beenpreviously trained in how to set up their chair and those subjects who said that they
had not. Seat height adjustment was used far more regularly than backrest height or
depth adjustment. W hereas only 7% of subjects reported never using seat heightadjustm ent, 28% reported never using backrest height ad justm ent and 29% reported
never using backrest depth adjustment. The majority of subjects reported only `very
rarely’ making adjustments to their chair, particularly backrest height. M any
subjects quali® ed this response with statements such as `Once I’ ve set it so that its
right for me I leave it there’ or `I only readjust it if someone else has been using mychair and changed it’ .
Chi-square tests showed that subjects who reported having had training in how
to set up their chair did not adjust it any more frequently than subjects who reported
having had no training. Of the 123 subjects, 38 × 5% of subjects reported having backpain, aching or discomfort within the last 6 m onths which they attributed to theirchair or o ce work. Of those subjects, 41% considered their back pain / discomfort
severe enough to seek professional advice.

Preferred chair settings for lumbar support
Table 3.

BM I
StatureGender411

Results of individual regression models examining the eŒects of standing height,
BM I and gender on lumbar support heights (LSH) recorded at T2, T3 and T4.
LSH at T2

LSH at T3

LSH at T4

Mean preferredLSHn.s. (p = 0 × 10)
n.s.
n.s.

p < 0 × 005
n.s.
n.s.

p < 0 × 001
n.s.
n.s.

p < 0 × 005
n.s.
n.s.

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3.3. Analysis
Each of the following statistical tests were preceded by standard diagnostics toensure that there were no major violations of the underlying assumptions.
3.3.1. Lumbar support height: In order to investigate whether subjects had speci® careas of preferred lum bar support within the availa ble height a random eŒects model
was used to estimate the components of variance at T2 and T4.
A relatively small variance within subjects compared to the variance between
subjects would have indicated that the m ajority of participants had speci® c height
preferences for lumbar support within the wider range of height adjustment
available. This was shown not to be the case. A total of 65% of the variance was
explained by within-subject diŒerences. None the less, the analysis showed highly
signi® cant diŒerences between subjects.
Spearman’ s correlation analysis showed that preferred lumbar support height
settings at T2 and T4 were signi® cantly related (p < 0 × 0001), indicating that whilesome subjects consistently preferred a higher lumbar support, others consistently
preferred a lower lumbar support.
A regression analysis was used to investigate whether the diŒerences in preferred
lumbar support height settings between subjects could be explained by diŒerences inphysical characteristics. A model, examining the eŒects of standing height, BM I and
gender on mean preferred lumbar support heights, showed a signi® cant positive
relationship between mean preferred lum bar support height and BM I (t 3 ,11 3 = 3 × 16;
p < 0 × 005). The gender and standing height of subjects did not signi® cantly in¯ uencemean preferred lum bar support height settings. Even though signi® cant, variationsin BM I explained only 8% of the variance in lumbar support height settings,
indicating that other unknown factors in¯ uence preferred lumbar support height
settings along with BM I.
Similar tests were carried out separately on the lumbar support height data frommeasurement sets T2, T3 and T4 (table 3). In each case, standing height and gender
showed no association with lum bar support height settings. BM I showed asigni® cant association with lumbar support height settings at T3 and T4, but was
not signi® cantly associated with settings at T2.
3.3.2. Lumbar support depth: A regression model examining the eŒects of standingheight, BM I and gender on preferred lumbar support depths showed no signi® cantrelationships (F (3 ,1 1 3) = 2 × 01; p = 0 × 116).
3.3.3. Adjustment characteristics: t-tests and Chi-square tests were used toinvestigate the characteristics of subjects displaying diŒerent ad justm ent strategies.
The 28 subjects who did not readjust their backrest from the disrupted position by412

N. Colem an et al.

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T4 were signi® cantly younger than subjects who did readjust (p < 0 × 05). Of these 28
subjects, 26 had their backrests disrupted to the most forward and lowest position,and two had them disrupted to the most forward and highest position. The lumbar
support height settings measured at T2 for the 26 subjects were signi® cantly lower
than those of other subjects (p < 0 × 05). Readjustment from the disrupted position was
not signi® cantly associated with reported back pain history or reported priortraining in o ce ergonomics.
Of the 80 subjects who readjusted their lumbar support by T3, 53% made further
readjustments by T4. The subjects who made further readjustments did not report
any more or less back pain than other subjects, were no older, and had had no moretraining in chair adjustment than the subjects who made a single readjustment fromthe disrupted position.
3.3.4. Back pain: A t-test was used to investigate the eŒects of recent back pain /discomfort on mean preferred lumbar support height settings. Subjects who
answered `yes’ to the question. `In the last 6 months, have you had any back pain,
aching or discomfort which you think might be related to your chair or o ce work?’
were found to set their lumbar support signi® cantly lower and further forward thansubjects who answered `no’ . Recent back pain was therefore built into the regression
model with BM I, stature an d gender to m ore accurately determ ine its aŒect on mean
preferred lumbar support height and mean preferred lumbar support depth. Thisre® ned model showed that recent back pain / discom fort did not signi® cantly aŒect
lumbar support height settings after adjusting for the eŒects of BM I, stature andgender. However, recent back pain was shown to be signi® cantly associated withdepth settings (p < 0 × 05) with suŒerers preferring their lum bar support signi® cantly
closer to the front of the seat.
4. Discussion
4.1. Preferred lumbar suppo rt height settings
The present research provides some evidence to support the inclusion of adjustable
lumbar support height in o ce chairs. The most important ® nding is that BM I wasstrongly associated with preferred lumbar support height settings whereas stature
was not. In the study population, BM I is more likely to represent an index of obesity
than muscular developm ent. This indicates that more obese people, regardless ofheight, prefer sitting on an o ce chair with a higher lumbar support and that
slimm er people prefer sitting on an o ce chair with a lower lumbar support. For
several reasons, this is a very important ® nding.
The ® rst is that given the variation in body sizes of the Australian multicultural
white collar workforce, a single ® xed height lumbar support is likely to result inincreased discomfort, or reduced com fort, for a high proportion of users compared
to a lumbar support that is appropriately adjusted for individual BM Is. The second
reason is that this ® nding provides the ® rst research-based justi® cation for the
inclusion of lumbar support height adjustment in o ce chairs. The third is that it isvery often assum ed that it is the very tall and very short people who may not be fully
accommodated at a ® xed height backrest (Lueder 1994 , CEN 1994 ) rather than theplump or the slim.
The association of preferred lumbar support height with BM I has several
possible explanations. For more obese people with more weight around the buttocks,
it is likely that a higher lumbar support may be necessary to provide adequateDownloaded by [University of York] at 11:03 08 October 2014

Preferred chair settings for lumbar support

413

clearance for the extra padding around the buttocks. It is also possible that the extra
fat tissue under the buttocks may raise the sitter so that their lum bar spine iseŒectively higher above the compressed seat ± requiring a higher lumbar support
height. A lot of fat around the buttocks and the lower back m ay also reduce thesitter’ s sensitivity to the position of their lumbar support. The extra padding could
prevent the lumbar support from ® tting snugly into the sm all of the back, therefore
reducing its eŒectiveness. This may lead to larger users not fully appreciating thebene® ts of lumbar support and preferring to set it higher for use as a generalbackrest. Finally, it is possible that bulkier people do not require the sam e degree ortype of support when sitting as do slimmer people. The extra body tissue may help to
support the sitting posture.
Several studies (Grandjean et al. 1969 , Fernand and Fox 1985 , Bodguk andTwomey 1987 ) have highlighted anatomical and physiological diŒerences between
males and females, which could result in signi® cant diŒerences in preferred lumbar
support heights. No diŒerences were observed in the preferred lumbar support
heights of males an d females in this study.
In discussing the issue of ® xed versus adjustable height lumbar supports it would
be inappropriate not to mention the research by Andersson et al. (1979), which hasprovided the basis for many arguments in favour of the ® xed height option. Theirradiological study revealed that the shape of the lumbar curves in 10 young healthy
males were not signi® cantly aŒected by variations in the height of lum bar support
from L1 to L5. This ® nding could be interpreted as m eaning that the height of alumbar support need not be exact and can be positioned anyw here within the L1 to
L5 range. However, like many clinical studies, one of the major limitations of thisresearch is that it focuses entirely on one function of lumbar support (maintaining
lumbar lordosis) and ignores the others (stabilizing the pelvis, minimizing themuscular eŒort required to support the trunk and relieving the low er spine of someof the upper body weight). This limitation was recognized by Andersson who
continued to recommend adjustable height lum bar supports (Andersson et al. 1991).
Sitting comfort and user preference is commonly used and widely regarded as one of
the best overall indicators of good seats and healthy sitting postures (Burandt andGrandjean 1963 , Branton 1969, Kroemer and Robinette 1969 , Shackel et al. 1969,
Kroemer 1971, 1994). Accordingly, the present study investigated the preferredsettings and adjustment behaviours of o ce workers trying to achieve the most
comfortable lumbar support in their usual o ce environm ent.
4.2. Do people use adjustm ents?
The establishment of a relationship between preferred lum bar support height settings
and the physical characteristics of individuals does not necessarily imply that heightadjustable lumbar supports are necessary. Research indicates that many users,
particularly those who have not had speci® c training, fail to make use of the chairadjustm ents provided (W ebb et al. 1984 , Shute and Starr 1984 , Lueder 1994). On thispremise, there remains a strong argument for a well-positioned ® xed height lumbar
support that provides the best compromise for the full range of potential users.
However, from a review of the literature, Lueder (1994) concludes that people
consider adjustability important and will use controls frequently if they are easy to
use and circumstances are good.
The majority of subjects in this study did not make adjustments to the height anddepth of their lumbar support. Prior to receiving the information on how and why toDownloaded by [University of York] at 11:03 08 October 2014

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N. Colem an et al.

make adjustments, only 29% of subjects reported never using backrest heightadjustm ent and 28% reported never using backrest angle for depth adjustm ent.
W hile some subjects appeared to prefer a set position for lumbar support, others
preferred to make more regular adjustments to its position.
A high proportion of subjects continued to adjust both the height and depth of their
lumbar support after the time when they believed the research had ended and their
settings were no longer being monitored. Of the subjects who readjusted their lumbar
support to a m ore appropriate position by T3, 53% had readjusted it again by T4, 4
weeks later. Some 39% of the subjects readjusted the height of the lumbar support and
45% readjusted the depth. These subjects were either not happy with their initial choiceof lumbar support height / depth, or they preferred to make more regular adjustments
to its position because of task diŒerences or the need to support diŒerent postures. For
whatever reason, a ® xed height lum bar support would clearly have interfered with thepreferred adjustment behaviours of a considerable proportion of users.
In contrast, another distinct group of users appeared not to be concerned about
the height of their lumbar support. By the measurement set T3 (4 ± 5 days after all
backrests had been set to the most forward an d lowest position) 35% of subjects had
failed to readjust their backrests. Since work activities and absenteeism were notmonitored during this period, it is unclear if this is a true representation of thenumber of subjects who were not concerned about the position of their lumbar
support. Even by T4, when all subjects should have had am ple opportunity toreadjust if desired, 23% of subjects still had not done so. This group was signi® cantly
younger than the rest of the subjects, suggesting that older users may be moresensitive to the position of their lumbar support. This supports the observations of
Keegan and Nebraska (1953) and Branton (cited in Corlett 1989) that younger
people are able to subject their lumbar spines to considerably more stress and strain
than older people without experiencing discomfort, and it adds weight to theargument of Keegan and Nebraska (1953) who emphasize the importance of a wellpositioned lumbar support to minimize sitting discomfort for users with degeneration of the intervertebral discs. Changes in mobility and degeneration of the lumbar
vertebrae and intervertebral discs with age is well documented (Bodguk and Twomey
1987 , Floyd and Roberts 1958 , Keegan 1962, K roemer and Robinette 1969 , M cCall
1992). The sensitivity of older people to the height of their lumbar support should
not be disregarded given the ageing workforce.
4.3. Com fort ranges
Several ® ndings of this research suggest that, rather than having speci® c lumbar
support height preferences, people may have `comfort ranges’ for lumbar support
height settings. It is possible that only when the lumbar support is positioned outsideof this comfort range do people perceive a reduction in com fort (or the onset of
discomfort) and decide to readjust. Three separate ® ndings support this theory:(1) The subjects who did not readjust when their lumbar support was m oved toits lowest and most forward position were the people who selected lower
lumbar supports as their preference for T2. It seems likely that in its lowest
position the lumbar support was still within the com fort range of thesesubjects.
(2) The components of variance analysis indicate that people do not have smalland speci® c regions of personal preference for lumbar support height.

415

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Preferred chair settings for lumbar support

Figure 7.

Representation of possible lumbar support height measurements for threehypothetical subjects at T2 and T4.

However, other testing clearly highlighted system atic diŒerences between
subjects.
(3) W hile BM I showed a highly signi® cant association with lumbar support
height settings at T4 (p < 0 × 001), it was not signi® cantly associated withsettings at T2 (p = 0 × 10). The concept of comfort ranges may go some way
towards explaining this. Since backrest heights started oŒwidely distributed
across the availa ble range, lumbar support height settings at T2 could havefallen anyw here within each individual’ s comfort range. The measured
lumbar support height at T2 could therefore have been tow ards the top of anindividual’ s comfort range, towards the bottom of their comfort range, or416

N. Colem an et al.
somewhere in the middle. Possible measurements for three hypotheticalsubjects at T2 are represented by dots ( ) in ® gure 7. The vast majority ofbackrests were set to the lowest position before subjects readjusted for T4.
Presumably, since subjects had to adjust their lumbar support upwards, themajority of settings for T4 are towards the bottom end of most individuals’
comfort ranges (see the hypothetical settings represented by crosses ( ´ ) in
® gure 7). The respective positions of these settings, while being lower, would
provide a m ore comparative representation of each subject’ s mean preferredsetting, of which the best estimate is associated with BM I (p < 0 × 005). On
average lumbar support heights measured at T4 were shown to besigni® cantly lower than lumbar support heights m easured at T2 by 12 mm .

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If the concept of individual comfort ranges is pursued, this study indicates thatthe centrepoint of an individual’ s comfort range above the seat (or their `mean
preferred setting’ ) is partly a function of the individual’ s body mass index. It could
also be argued that the size of an individual’ s comfort range is to some extent
determined by their age, with younger people generally being more tolerant of awider range of lum bar support heights.
4.4. EŒects of back pain
The adjustment patterns of subjects who had experienced long-term back pain did
not diŒer from other subjects. However, subjects who experienced back pain, achingor discomfort in the last 6 months, which they thought might be related to their chairor o ce work, were found to set their lumbar support signi® cantly closer to the frontof the seat than subjects who had not. The most likely explanation for this is thatpeople with back pain adjust their lumbar support further forward so as to ensure
maximum support for the back.
4.5. Lumbar support depth
There were no other associations between subject characteristics and preferred lumbar
support depth. Initially it appears surprising that the depths chosen by subjects wereentirely independent of stature. H owever, various other studies report a similar lack ofassociation between upper leg (buttock to popliteal) length and the preferred distancefrom the front of the seat to the backrest (Le Carpentier 1969 , de Groot and Vellinga1984). There are several possible explanations as to why taller users may not set their
lumbar support further back from the front of the seat. First, while the seats of thestandard chairs used in this study were essentially ¯ at and not excessively dipped or
shaped, the seat provided a de® nite target area for the buttocks. Placem ent of the
buttocks further back on the seat would alm ost certainly result in a less even
distribution of pressure over the buttocks and upper thighs. Second, sitters frequently
like to change their posture (Branton 1969 ) and regular postural changes when sitting
are often recommended (W inkel and Oxenburgh cited in Lueder et al. 1994). The moreof the thighs that are supported by the seat, the more di cult it is to change posture.
Consequently, many taller users m ay choose not to set their lumbar support further
back in order to take advantage of the extra seat depth. Another explanation could bethat subjects set their seats higher than is generally recom mended as a result of the ® xed
height desks at which they worked. Higher seats encourage users to sit further forward.
The lumbar support depth measurem ents recorded in this study indicate that
subjects most commonly prefer short lum bar support depths, preferring the backrestPreferred chair settings for lumbar support

417

closer to the front of the seat. It is possible that many subjects would have set their
lumbar support even closer to the front of the seat if the option had been availa ble tothem.
4.6. Design guidelines
The following recomm endations can be made concerning the design of chairs withlumbar supports adjustable in both height and depth.

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The ® ndings of this study indicate that many current recommendations forlumbar support height adjustability may be too high (DIN 1987, Pheasant1990 , W orksafe Australia 1991). The present results suggest that, for the
majority of users to be able to achieve their preferred lumbar support height
settings, the lumbar support point should adjust from 150 mm to 250 mmabove the compressed seat. Certainly the results indicate that, for a lumbar
pad with sim ilar shape and contouring to the test chairs, the centrepoint of
the adjustment range should be no higher than 200 mm above thecompressed seat surface.
(2) To encourage adjustm ent, controls must be easy to use. This study foundthat lum bar support depth was more frequently adjusted than lumbar
support height. This may be at least partly due to the relative ease of use of
the adjustment controls. M any other studies have linked the appropriate useof adjustments with their ease of operation (Hozeski 1986, Lueder 1994 ,DainoŒcited in Lueder 1994).
(3) Lumbar support height ad justment probably does not need to becontinuous. Given that users have com fort ranges for lum bar support
height, the provision of four or ® ve discrete options spread across the total
range is likely to be just as suitable as a continuous system.
4.7. Limitations
Design issues associated with the manufacture of ergonomic chairs for contem poraryo ce tasks are very complex. Despite increased aw areness of ergonomics andrecommended sitting postures, people continue to spontaneously adopt postures thatare considered undesirable. M any studies show that people do not necessarily preferchairs that correspond to their anthropometric dimensions and frequently fail toadjust chairs accordingly (Burandt and Grandjean 1963, LeCarpentier 1969 , Shackel
et al. 1969, deGroot an d Vellinga 1984 , Lueder 1994). W hile this study has
demonstrated that people do adjust their chairs, and that there is a strong
association between preferred lumbar support height and body mass index, the factthat BM I still only explains 8% of the variance shows that there remains a number ofother unexplained variables that aŒect how high a person likes their lumbar support.
These may include variations in sedentary work tasks and temporal factors.
The results of this research can only be interpreted in term s of traditional paddedo ce chairs. The indication that ® xed height lumbar supports are unlikely to provide
a comfortable or appropriate seat for the wide range of potential users may not
apply to other designs that make use of diŒerent materials and mechanisms.
5. Conclusion
Based on the evidence that a high proportion of users do make adjustm ents to theheight and depth of their lumbar support, and the ® nding that diŒerent groups of

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N. Colem an et al.

users, with diŒerent physical characteristics, adjust the position of their lumbar
support in distinct and predictable ways the researchers conclude that chairs witheasy-to-use lumbar support height adjustment must be recommended for contemporary o ce work.
Acknowledgements
The authors would like to acknowledge the valuable advice and assistance given by
Dr M ike Stevenson and Dr John Brotherhood.

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