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Ryan, C. G. et. al. (2011) 'Sitting patterns at work: objective measurement of
adherence to current recommendations', Ergonomics, 54 (6), pp.531-538.
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http://dx.doi.org/10.1080/00140139.2011.570458
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1
Title
Sitting patterns at work: objective measurement of adherence to current
recommendations.
Running title
Sitting patterns at work.
Authors names
Cormac G Ryan
1
, P Margaret Grant, Philippa M Dall, Malcolm H Granat.
Affiliation
School of Health, Glasgow Caledonian University, Scotland, UK, G4 0BA.
1
Corresponding Author: Dr. Cormac Ryan Ph.D. telephone (0044) (0)1642 384916; email:
c.ryan@tees.ac.uk
2
Abstract
Long uninterrupted sedentary periods, independent of total sedentary time, are risk
factors for poor health. There is little objective data relating to workplace sedentary
behavior and adherence to current recommendations. The sitting behaviour of office
workers (n=83) was quantified objectively using body-worn accelerometers
(activPAL™) over a working week. Adherence to three different recommendations
(maximum length of a sitting event of: 20minutes, 30minutes and 55minutes) were
assessed. Participants were seated at work for 5.3±1.0hours/day (Mean±1SD),
equivalent to 66±12% of the working day, accrued in 27±7events/day individual
sitting events. Dependent on the recommendation applied, 5-20% of sitting events and
25-67% of time was accumulated in sitting events longer than current guidelines. No
participants met the 20 or 30minutes recommendations on every working day but
seven (8%) participants met the 55minutes recommendation. In conclusion, office
workers spend a considerable period of their day sitting, accumulated in uninterrupted
sitting events longer than current recommendations.
Key words
Sedentary; sitting; behaviour; adherence; activPAL™
Statement of relevance
Emerging evidence suggests prolonged sitting has negative health effects. In this
study of office-workers 25-67% of time sitting was accumulated in events longer than
minimum recommended durations. Adverse sitting behaviour is prevalent in the office
making it an appropriate setting to target the reduction of this behaviour.
3
1. Introduction
Moderate to vigorous physical activity (MVPA) can have a beneficial effect on many
health conditions such as cardiovascular disease, type II diabetes and obesity (Pate et
al. 1995; Haskell et al. 2007). Very specific MVPA guidelines for adults exist,
recommending 30 minutes of moderate intensity activity on most days of the week to
be accumulated in bouts of 10 minutes or more (Haskell et al. 2007). It has been
argued that many modern day occupations require too little MVPA and that strategies
should be put in place to increase physical workloads in the workplace (Straker and
Mathiassen 2009).
Sedentary behaviour can be defined as time spent sitting (Biddle 2007;
Katzmarzyk et al. 2009; Owen et al. 2009) or sitting/supine (Chastin and Granat
2010; Jans et al. 2007). Recently, it has been shown that sedentary behaviour is a risk
factor for many health conditions often independent of MVPA (Healy et al. 2008a;
Katzmarzyk et al. 2009). Additionally, there is preliminary evidence that it is not just
the total sedentary time which is relevant but the manner in which it is accumulated;
longer sedentary events being associated with undesirable health markers (e.g. a large
waist circumference) compared to shorter sedentary events (Healy et al. 2008b; Healy
et al. 2011). Despite this, there are no official national guidelines for sedentary
behaviour. The recommendations that do exist are few in number, vary in their
advice, and appear to be based upon expert consensus rather than robust scientific
evidence (Atlas and Deyo 2001; Chartered Society of Physiotherapy 2005; Owen et
al. 2009).
Many occupations are computer-based, and this results in predominantly
seated behaviour at work (Hill and Peters 1998; Smith et al. 1999). Data from a range
of industrialised countries, including Sweden, U.S.A, Australia and New Zealand,
suggests that increased sedentariness at work is an international phenomenon (Straker
and Mathiassen 2009). While the biomechanical aspects of seating and sitting have
been subject to extensive research (Corlett 2006; Page et al. 2009), behavioural
aspects of sitting at work have not received the same level of attention. McCrady and
Levine (2009) identified that workers in the USA were sedentary for approximately
two hours more on working days compared to leisure days. Workers were classified
as having jobs that were either “entirely sedentary” (chair bound most of the day) or
“semi-sedentary” (intermittently standing and chair-bound but without substantial
4
walking or physical labour) (McCrady and Levine 2009). A recent report on the
sitting behaviour of office-based workers in Australia found employees were sitting
for 77% of their time at work (Thorpe et al. 2008). Thus the work place is a setting
where sedentary behaviour is highly prevalent, and this presents an important location
where strategies to reduce sedentary behaviour should be introduced (Hamilton et al.
2008; McCrady and Levine 2009). However, without clear evidence based guidelines
targeted strategies are difficult to design and implement.
A literature search identified three different recommendations which specified
maximum sitting time; 20 minutes (Chartered Society of Physiotherapy 2005), 30
minutes (Atlas and Deyo 2001), and a five minute break every hour (Owen et al.
2009). The 20 minute recommendation was taken from the Chartered Society for
Physiotherapy, Fit-for-work initiative (Chartered Society of Physiotherapy 2005) and
the 30 minute recommendation was based upon information given to individuals with
acute low back pain (Atlas and Deyo 2001). The development of both of these
recommendations was rooted in musculoskeletal medicine. In contrast, the five
minute breaks every hour recommendation, was developed with a focus on metabolic
health, and was based upon the potential clinical implications of normative
objectively measured sitting data (Owen et al. 2009). However, all three of these
recommendations appear to be based upon authors’ professional judgment rather than
robust scientific rationale.
A first step towards developing more evidence based guidelines should be to
collect objective normative data of sitting behaviour in the work place and assess
adherence to current recommendations. Whilst recent research has objectively
quantified total sitting time at work (Thorpe et al. 2008; McCrady and Levine 2009),
this data has been collected using accelerometer counts as a proxy for sitting times
rather than using devices that directly measure sitting. Additionally, there has been no
published data on sitting patterns such as the length of individual sitting events. Such
information may help develop an understanding of what type of sitting
recommendations may be practical to achieve and guide future interventions to reduce
sedentary behaviour. The aim of this study was to objectively quantify patterns of
sitting behaviour in an office setting and to assess adherence to current sitting
recommendations
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2. Materials and methods
2.1 Design
In this observational study, which is a reanalysis of data collected for another study,
the sitting behaviour of office-based employees during working hours over a one-
week period was recorded using activity monitoring. The total sitting time
accumulated and the patterns of sitting behaviour were quantified and compared to
current sitting recommendations within the literature.
2.2 Participants
Participants for this study were selected from a database of free-living physical
activity profiles of healthy adults. Participants were recruited onto the data-base using
recruitment emails circulated to staff and postgraduate students of Glasgow
Caledonian University. Participants were included on the data base if they were aged
≥18 years, lived in the community, had no mobility problems and were not expecting
to experience any unusual activity in the monitoring week (e.g. on vacation).
Participants from the database were selected if they worked in an office-based
occupation, classified as entirely sedentary (chair bound most of the day) or semi-
sedentary (intermittently standing and chair-bound but without substantial walking or
physical labour) as defined by McCrady and Levine (2009). For individuals that did
not provide clear indication of which days were working and non-working, weekdays
were considered to be working days. Any individual who worked part-time but did
not indicate which days they worked were excluded from the data set. Participants
were also excluded from the data set if the number of working days recorded was less
than three days. Ethical approval was received from the Glasgow Caledonian School
of Health and Social Care research and ethics committee. All participants provided
written informed consent.
2.3 Procedure
Sedentary activity was measured over a seven day period between October 2007 and
October 2009 in Glasgow, Scotland. A time frame of 9:00am to 5:00pm on working
days was selected to represent time at work. This time frame was selected to represent
the usual working hours of Glasgow Caledonian University staff. Sitting events which
6
crossed this time boundary were also included if more than half of that event was
within the 9:00-5:00pm time frame.
2.4 Physical activity monitor
Physical activity was measured using the activPAL™ physical activity
monitor. The activPAL™ is an accelerometer based device which is worn on the
thigh. The monitor produces a signal which is related to the inclination and movement
of the thigh. From this signal it can directly identify time spent in the postures of
sitting/lying, standing and walking on a second by second basis. The monitor has been
shown to be a valid (>99% sensitivity and specificity) and reliable (ICC >0.99)
measure of sitting posture (Grant et al. 2006). The activPAL™ is small and
unobtrusive requiring little input from the wearer. These issues of accuracy and low
burden are important when measuring exposure to risk factors in an office
environment (Van Eerd et al. 2009).
2.5 Data analysis
Three sitting activity outcome measures were calculated for the whole group and for
occupational subgroups; 1) the total number of sitting events/day 2) the total times
sitting/day and 3) the mean of the longest sitting periods for each participant.
Adherence to sedentary recommendations was then assessed. Adherence to three
separate recommendations were used in this study; a maximum sitting time of 20
minutes (Chartered Society of Physiotherapy, 2005), a maximum sitting time of 30
minutes (Atlas and Deyo, 2001), and a five minute break every hour (Owen et al.
2009). The latter recommendation was operationalised as a maximum sitting time of
55 minutes.
The activPAL™ software (version: 5.9.1.1) classified the acceleration signal
into sit/lie, stand and walk. In-house purpose built software (written in visual basic for
applications, to run in excel), was used to present data by event and to select data
between 9 and 5pm on work days. Visual inspection of the day was used to identify
workdays and check whether the first and last periods should be included. A number
of different outcome measures were calculated from the sitting data. For the whole
sample, total sitting time, total number of events and total time and number of events
longer than 20 minutes, 30 minutes and 55 minutes were derived. An event is defined
7
as a single uninterrupted sitting period. These were calculated from cumulative
frequency graphs of sitting activity as a proportion of number of events and total time.
For each participant, the longest sitting event was reported. In addition, the number of
sitting events greater than 20, 30, and 55 minutes in each day was calculated. From
this, the number of days in which the sitting recommendations were met for each
individual was identified. Individuals were deemed to have met the guidelines if they
met the criteria for each working day assessed.
Different subgroups of office-based worker, based on self-reported job
description, e.g. lecturer, technician were identified. Differences between subgroups
for basic demographics and the key sitting outcome measures were compared using a
one-way ANOVA with the Statistical Package SPSS (Version 18.0).
3. Results
From a physical activity database of 121 individuals, data from 83 participants were
included in this study. The remaining 38 participants were excluded as; they were not
office-based, there was insufficient information to allow classification as an office-
based employee or to identify their work days, or there were less than three working
days recorded. Of the 83 participants included, four occupational subgroups were
identified; 27 lecturers, 27 researchers (desk-based), 7 technicians and 22
administrators. One way ANOVA revealed significant differences between
occupational subgroups for age (lecturers were statistically older than researchers and
administrators) and BMI (no significant post-hoc differences); there were no
statistically significant differences in descriptive characteristics between the
subgroups. Participant characteristics are shown in Table 1. Data were available over
five working days for the majority of participants (n=60). The minimum number of
working days recorded was three (n=6) and the maximum was six (n=1).
Insert Table 1 here
3.1 Sitting time
For the group as a whole, 66±12% [range 31-90%] (mean±1SD [range]) of time at
work was spent sitting. The total time spent sitting by participants during 388 working
8
days was 2,042hours (5.3±1.0 hours/working day [range 2.5-7.2]), which was
achieved in a total of 9,918 (27±7 events/working day [range 13-48]) individual
sitting events. The mean of the longest sitting event of each participant was 98±34
minutes [range 43- 201]. There was no statistically significant difference between the
four occupational subgroups for total sitting time or the number of sitting events,
though there was a trend for the technicians to spend less time sitting and accumulate
more sitting events (Figure 1). There was a statistically significant difference between
the occupational subgroups for the mean longest sitting period (p<0.01). The
technicians’ mean longest sitting period was shorter than for the researchers (Figure
1).
Insert Figure 1 here
3.2 20 minutes recommendation
Figures 2 and 3 show a cumulative frequency graph of the duration of sitting as a
proportion to the cumulative number of sitting events (figure 2) and the cumulative
sitting time (figure 3) standardised to the number of working days. The horizontal
lines identify how sitting behaviour relates to the 20, 30 and 55 minute sitting
duration recommendations.
Of the total sitting time, 20% of events and 67% of time was in single duration sitting
events that lasted longer than 20minutes (figure 2 & 3; Table 2). The most sitting
events taken by a participant which were longer than the recommended duration of 20
minutes in a single working day was 11 (from a maximum possible of 23 events).
Five (6%) participants met the recommendation on at least one of the days observed
and none of the participants met the recommendation for sitting in periods of no
longer than 20 minutes for every working day assessed.
Insert Table 2 here
Insert figures 2 and 3 here
3.3 30 minutes recommendation
9
Of the total sitting time, 12% of events and 52% of time was in single duration sitting
events that lasted longer than 30 minutes (figure 2 & 3; table 2). The most sitting
events taken by a participant which were longer than the recommended duration of
30minutes in a single working day was 7 (from a maximum possible of 15 events).
Fifteen (18%) participants met the recommendation on at least one of the days
observed. None of the participants met the recommendation for sitting in periods of
no longer than 30 minutes for every working day assessed.
3.4 55 minutes recommendation
Of the total sitting time, 5% of events and 25% of time was in single duration sitting
events that lasted longer than 55 minutes (figure 2 & 3; table 2). In a single working
day, the maximum number of seated events recorded which were longer than 55
minutes was four (out of a maximum of seven possible sitting events). Sixty-one
(73%) of participants met the recommendation on at least one of the days observed.
Seven (8%) of the participants met the recommendations for sitting in periods of no
longer than 55 minutes for every working day assessed. It is worth noting that a
greater percentage of technicians (43% [n=3]) achieved the 55 minute
recommendations on all working days compared to the other occupation categories.
However, small subgroup numbers prevent more in-depth statistical analysis.
4. Discussion
This study adds to the small amount of objective data available which reports the total
time spent sitting in an office-based environment. Additionally, this is the first study
to objectively quantify the sitting patterns of office-based individuals in the work
place environment, and it is the first to investigate adherence to current subjective
recommendations on sitting behaviour. Total sitting time was approximately 66% of
the total time spent working, of which 5-20% of events, and 25-67% of time was in
single duration events that lasted longer than the recommended minimum duration,
depending upon which recommendations were applied. None of the participants met
the recommendation for sitting in events of less than 20 and 30 minutes duration on
every day of the week. But 7 (8%) of participants did meet the 55minutes
recommendations on every day of the week and 61 (73%) on at least one day a week.
10
The reasons for such poor adherence to recommendations are unclear. Current
recommendations are not well publicised. As such, it is difficult for individuals to
comply with recommendations of which they are likely unaware. It may be that
recommendations are not well advertised because there exists little or no consensus
on what is appropriate. Current recommendations for sitting appear to be based on
expert consensus rather than strong scientific evidence (Atlas and Deyo 2001;
Chartered Society of Physiotherapy 2005; Owen et al. 2009). There is a need for more
robust basic data to be collected to facilitate the development of comprehensive
sedentary behaviour guidelines (Healy et al. 2008b). Previous research on other health
behaviours has identified the importance of using clear messages to facilitate uptake
of effective behaviour change strategies (Pechmann and Reibling 2000). Similarly,
clearer recommendations on sitting duration would likely increase adherence to sitting
guidelines.
Poor adherence may also be the result of current recommendations being
unachievable in today’s workplace and future guidelines need to be sensitive to this.
If a health goal is to be motivating it should be achievable so that the individual can
experience some success which can be used as a platform to encourage further
behavioural change (Klein et al. 2004), otherwise it may have a negative or
demotivating effect resulting in even poorer adherence. This provides some support
for the use of the 55 minute recommendation as they are clearly achievable. They
were the only current recommendations where any participants achieved the
recommendations every working day assessed and considerably more participants
achieved the recommendations on at least one day (73%) compared to the other
recommendations used in this study. However, simply because the recommendation is
more achievable should not be the only reason for adopting a certain sitting
recommendation at work. More research is required to quantify the appropriate length
of sitting periods for health and wellbeing before firm recommendations are made.
The data presented here could be used to develop future recommendations.
For example, depending on the recommendation applied, the mean number of events
lasting longer than recommended ranged from 1-5 events per day. This is a relatively
small number of events which need to be targeted. Such targeting could involve
simple workplace restructuring to interrupt these longer sitting events e.g. placing
printers away from the PC. The National Institute for Health and Clinical Excellence
11
(NICE) highlights how architects, designers and facility managers should engage with
such simple workplace environment ogranisation to maximize physical activity e.g.
ensuring staircases are well signposted and appropriately positioned to make them
more attractive to use (NICE 2008). However, the evidence to support such strategies
is lacking (Dugdill et al. 2008). There is a need for future research to investigate if
adverse sitting behaviour could be reduced in the workplace using simple
environmental interventions.
There have been a number of articles which have objectively assessed
adherence to MVPA guidelines, and only a small percentage (<5%) of individuals met
current American College of Sports Medicine physical activity guidelines (Troiano et
al. 2008; Chastin et al. 2009). The current study is the first to specifically investigate
adherence to sedentary recommendations. The results of this study suggest a similar
low level of adherence (0-8%) highlighting the need to address adherence issues for
this behaviour.
A small number of studies have attempted to objectively quantify free-living
sedentary behaviour (Levine et al. 2005; Thorpe et al. 2008; Matthews et al. 2008;
McCrady and Levine 2009). Matthews et al. (2008) identified that Americans spend
54.9% (7.7hours/day) of their waking day sedentary. The reason for the difference in
total sedentary time for the current study and that of Matthews et al. (2008) is likely
due to differing methodology. Matthews et al. (2008) looked at individuals in
America >6years-old during their waking day, whilst the current study looked at
adults UK workers during their 9:00 – 5:00am working day. A recent report on the
sitting behaviour of office-based workers in Australia, found 77% of employees time
at work was spent seated (Thorpe et al. 2008). Discrepancies between the current
study and Thorpe et al. (2008) could be related to differences in methodology, but the
information available for the Thorpe et al. (2008) study was limited, making
comparison difficult. For example, it was not identified what type of accelerometer
was used to quantify sedentary behaviour. The current study differs from all previous
research which have objectively measured sitting behaviour at work as it quantified
the pattern in which the sedentary behaviour was accumulated, which is itself an
independent risk factor for cardiovascular ill health (Healy et al. 2008b; Healy et al.
2011) and is directly linked to the achievement (or not) of current recommendations.
12
The sub-group analysis found a trend for the technician group to spend less
time sitting and have more sitting events compared to the other groups. Additionally
the mean longest sitting period was significantly shorted for the technicians compared
to the researchers. This suggests that technicians had less adverse sedentary patterns
than the other subgroups. It also suggests that the mean longest sitting period may be
a more sensitive measure of sedentary patterns than the other measures used. Overall
however, the difference in sitting behaviour between groups was relatively small and
may simply reflect the natural variation of sitting behaviour for different sedentary
office-based occupations. This arguably makes the study more reflective of real life
office work rather than looking at a very narrow office-based occupational group such
as administrative staff only. Alternatively, the different sitting behaviour between
groups may reflect differences in demographic characteristics between the
occupational subgroups.
This study had a number of limitations. A convenience sample of office-based
workers was used. Different office-based occupations may vary in their seating
behaviours, thus the findings may not be generalisable to all office-based workers.
Precise data on work hours were not available for each individual and so work time
was arbitrarily chosen to match the predominant prevailing work hours of the
occupations represented. As there was a lack of identifiable sedentary guidelines in
the literature, there were no strong criteria against which to assess adherence. The
recommendations identified were taken from relatively anecdotal suggestions and
may not be appropriate for guidelines. However, this limitation is a consequence of
the sparse literature in the area and identifying this lack of evidence provides a useful
starting pointing for the development and assessment of guidelines and adherence in
the area of sitting behaviour. A strength of this paper was the use of a direct measure
of sitting behaviour compared to some other studies which have indirectly measured
sedentary behaviour using low levels of accelerometer counts (Healy et al. 2008a;
Healy et al. 2008b; Matthews et al. 2008).
5. Conclusion
This study found that within the office-based working environment complete
adherence to current sitting recommendations ranged from 0-8%. 5-20% of sitting
events, and 25-67% of time sitting was accumulated in events that lasted longer than
13
the recommended minimum duration. This data reinforces previous research that the
work place is an environment in which exposure to adverse sedentary behaviour is
high and indicates that the workplace is a highly appropriate setting in which to target
the reduction of this behaviour.
Acknowledgments
This study was funded by the School of Health and Social Care, Glasgow Caledonian
University, and no financial support was received from any commercial company.
All authors contributed to the development of the research idea, collection of the data
and drafting the manuscript. The authors would like to thank Danny Rafferty for
creating figures 1, 2 and 3. The data for this article was collected by; Sebastien
Chastin, Elaine Coulter, Philippa Dall, Margaret Grant, Gillian MacLellan, and
Cormac Ryan.
Conflict of Interest Statement
One of the authors is a co-inventor of the activPAL™ physical activity monitor and a
director of PALtechnologies Ltd. The remaining authors declare no competing
interests.
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18
Figure legends
Fig 1: Mean and standard deviation of (a) number of sitting events, (b) total daily
sitting time and (c) duration of longest sitting event; by occupational subgroup.
Fig 2: Cumulative frequency graph of the duration of sitting as a proportion to the
cumulative number of sitting events standardised to the number of working days. The
horizontal lines identify how sitting behaviour relates to the 20, 30 and 55 minute
sitting duration recommendations.
Fig 3: Cumulative frequency graph of the duration of sitting as a proportion to the
cumulative sitting time standardised to the number of working days. The horizontal
lines identify how sitting behaviour relates to the 20, 30 and 55 minute sitting
duration recommendations.
19
Table 1: Participant characteristics
Total Group
(n= 83)
Lecturers
(n=27)
Researchers
(n=27)
Technicians
(n=7)
Administrators
(n=22)
Gender (male)
25 (30%)
6 (22%)
10 (37%)
4 (57%)
5 (24%)
Age (yrs)
40±10
48±8
34±8
42±9
39±9
Height (m)
1.70±0.08
1.69±0.07
1.71±0.09
1.73±0.08
1.69±0.09
Weight (kg)
72±13
70±12
71±11
71±12
77±17
BMI (kg.m2)
24.9±3.8
24.5±3.5
24.1±3.1
23.5±2.4
27.0±4.9
Table 1: Participant characteristics for total sample and its sub groups. Data are
presented as means ± standard deviation.
20
Table 2: Participant adherence to guidelines
20 minutes
30 minutes
55 minutes
Number of sitting events longer than
recommendations (number/day)
5.0±1.5
3.1±1.1
1.0±0.6
% of sitting events longer than
recommendations (%)
20±6
12±4
4±2
Sitting time longer than recommendations
(hrs/day)
3.6±1.2
2.8±1.1
1.8±0.9
% of sitting time longer than
recommendations (%)
64±14
51±14
31±15
Maximum sitting events in one day longer
than recommendations (number)
11 (max 23)
7 (max 15)
4 (max 7)
Participants meeting recommendations
every day(number)
0 (0%)
0 (0%)
7 (8%)
Participants meeting recommendations on
any day (number)
5 (6%)
15 (18%)
61 (73%)
Table 2: This table shows participants adherence to the three different guidelines Data
presented as mean ± standard deviation, number (max), or number (%).
Footnote; max = maximum; this relates to the maximum number of sitting events in
one day which were longer than the recommendations e.g. at least one individual had
11 sitting events in one day longer than 20 minutes out of a possible 23 events.
21
