Impact of sit-stand desks at work on energy expenditure and sedentary time: protocol for a feasibility study

The proposed feasibility study will consist of four phases (phases I–IV) (Fig. 1). Each phase will address different aims and employ a variety of methods for doing
so, including:

A survey (phase I)

Workspace auditing (phase II)

A cross-over randomised component (phase III)

Direct observations (phase III)

Qualitative interviews (phase IV)

Fig. 1. Study overview and participant flow


Participants will be office-based employees of two companies in Cambridge, UK.

Inclusion criteria

Work at least 0.6 full-time

Spend at least 70 % of a working week performing desk-related activities

Exclusion criteria

Are already using sit-stand desks

Do not have use of their own personal desk

Have musculoskeletal disorders that make prolonged standing inadvisable

Have chronic illnesses that prevent prolonged periods of standing

Are planning to be absent from the workplace for more than 14 working days during
the study period

Are pregnant

For phase I, 500 eligible employees will be targeted. Phase II will involve 100 participants.
Both phases III and IV will involve 20 participants.

Eligible participants will be identified and recruited through (i) employment databases
and invited via letter/email and (ii) adverts in local newsletters and flyers posted
within the buildings of target organisations.

Sample size

No formal sample size calculations are produced for this feasibility study. Sample
sizes for each phase (see Fig. 1) are chosen based on resources. However, it is possible to determine the precision
with which certain parameters can be estimated with the sample sizes chosen for each
of the study phases.

To achieve the target of 500 individuals completing phase I, the survey will be circulated
to approximately 1400 individuals. Although in organisational research the average
response rate from individual respondents is 53 %, we have based our estimate on the
conservative expected rate of 35 %, which is the average survey response rate for
organisational respondents 77]–79].

Based on the average interest rates reported in previous studies assessing the impact
of sit-stand desks on sitting time, the expected proportion of participants interested
in taking part in a trial of sit-stand desks at work is 37 %. With 500 participants,
the 95 % confidence intervals around an estimate of 37 % would be from 33 to 41 %.

Based on the average recruitment rates reported in previous studies assessing the
impact of sit-stand desks on sitting time, the expected recruitment rate is 33 %.
With 500 participants, the 95 % confidence intervals around an estimate of 33 % would
be from 29 to 37 %.

The average attrition rate between baseline and follow-up reported in previous studies
assessing the impact of sit-stand desks is 10 %. With 20 participants, the 95 % confidence
intervals around an estimate of 10 % would be from 2 to 33 %. The maximum attrition
rate reported in previous relevant studies is 14 %. With 20 participants, the 95 %
confidence intervals around an estimate of 14 % would be from 3.5 to 38 %.


Phase I

During phase I, approximately 1400 eligible participants from across organisations
will be invited to complete an online survey, of whom we aim 500 to complete the survey,
to assess the following: (a) their interest in participating in a trial aiming to
assess the use of sit-stand desks at work; (b) their preferences for different desk
types (full desks vs desk mounts); and (c) their preference regarding the location
(home vs workplace vs clinical research facility) for the baseline and follow-up assessments.

The survey will include a brief description of the trial and will ask people to indicate
their willingness to participate, via a yes/no response. The proposed duration of
the future full trial, the design of which this feasibility study aims to clarify,
is 6 months, Due to resource restrictions, the duration of the randomised component
of the proposed feasibility study will be 3 months. To gauge any potential differences
in interest to participate as a function of the trial duration, all participants will
be asked to respond to two relevant questions: one enquiring about their interest
in a trial lasting 3 months and one enquiring about their interest in a trial lasting
6 months. The order in which these questions appear will be randomised. Participants
will also be asked to indicate their preference regarding potential locations for
the assessments to take place (home, workplace, or clinical research facility).

The survey will also include a brief description, with pictures, of the two different
types of sit-stand desks available: full desks and desk mounts that are installed
on top of existing desks. Links to videos demonstrating how each desk type works will
also be provided.

The survey will also include questions relevant to participants’ demographic information,
including age, gender, level of education, BMI, smoking status, salary band, and position
within the organisation.

Phase II

Of the participants indicating an interest in taking part in the trial during phase
I, 100 chosen at random will be visited by a researcher who will assess their workspaces
for desk installation suitability. To do this, the researcher will measure the following:
(a) the dimensions of the workspace, (b) the dimensions of existing desks, and (c)
the dimensions of any available (empty) space. The researcher will also record (through
photographs and notes) the configuration of the space (i.e. shape of the room) and
of the furniture within that space, making note of any obstacles that might inhibit
desk installation and/or use (e.g. shelves that would obstruct sit-stand desks being
put into standing mode).

These measurements and records will be compared against measurements involving the
space and room configurations needed to successfully install each desk type, identified
from measuring acquired samples of each desk type.

Phase III

Twenty randomly selected participants of those whose workspaces will be measured during
phase II will be randomised to either the use of sit-stand desks (full desks or desk
mounts depending on their preference and workspace limitations) at work for 3 months
or a waiting list control group. Those allocated to the waiting list control group
will continue using their existing desks and will be offered sit-stand desks 3 months


The intervention will comprise the provision of sit-stand desks at work for 3 months.
Participants will be offered one of the two desk types according to their preferences
and workspace restrictions: desk mounts or full desks. This is in line with the procedures
adopted in previous studies 54], 69] and is expected to maximise the probability of desk use. Desk mounts involve a device
that is installed on top of a conventional workplace desk often by means of a clamping
arm. The device facilitates regular transitions between sitting and standing postures,
predominantly while performing computer-based activities. It can be placed in standing
mode via an easy upward pulling motion that lifts the display unit(s) and objects
placed on the work surfaces. With full sit-stand desks, the entire surface area of
the desk (and all items on it) can be adjusted to standing mode.

To enhance desk use, participants will also be given the following: (i) a demonstration
of how their desk works, delivered in person by a researcher; (ii) written instructions
on how to use the desks; (iii) information on the correct ergonomic posture; (iv)
information on the benefits of standing, reducing sitting and breaking up sitting
time; (v) guidance on gradually building up standing time; (vi) recommendations relating
to the amount of time to increase standing and reduce sitting; and (vii) information
on how the desks are used by others.


Following baseline assessments, participants will be randomised to the use of sit-stand
desks at work or a waiting list control group, who will receive sit-stand desks 3 months
later. The randomisation will be determined by a statistician independent from the
research team, with the assistance of computer software.


Of those randomised during phase II, 10 participants, five from the interventions
group and five from the waiting list control group, will complete the baseline and
follow-up assessments.

Based on their preference of location, participants will be visited by a researcher
at their home, or place of work, or invited into a clinical research facility for
all baseline assessments to be made prior to randomisation. The measurements will
include anthropometric (height, weight, fat mass, fat-free mass, waist and hip circumference)
and blood pressure measurements and collection of a blood sample to measure total
cholesterol, HDL, triglycerides and HbA1C. Participants will also be asked to complete
a questionnaire to assess musculoskeletal discomfort and other health symptoms, ability
to work, presenteeism, absenteeism and job satisfaction, quality of life and domain-specific
sedentary behaviour.

They will also be fitted with a combined heart rate and movement sensor (Actiheart)
on the chest and asked to complete either a stepping test, if assessed at home or
work, or a treadmill test if assessed in the clinical research facility. They will
also be fitted with a thigh-based accelerometer (activPAL) to measure baseline sitting
standing and stepping time and sitting and standing patterns. Both devices will be
worn for 24 h/day for seven consecutive days. Participants will also be required to
complete a brief daily log with wake and sleep times, work hours and any device removal,
as well as their food intake. Participants will receive instructions on devices and
log use. Devices and logs will be collected by research staff at the end of the 7-day

Follow-up assessments will occur 3 months after baseline. One week prior to this,
participants will be visited by a research assistant who will fit them with the inclinometers
and monitors, to be worn 24 h/day for seven consecutive days. Data from these will
be used to assess the impact of the intervention on sitting and standing time, as
well as sitting and standing patterns, and physical activity energy expenditure. Participants
will also be asked to complete the daily logs. Seven days later, depending on participants’
location of preference, devices and logs will either be collected by research staff,
who will visit participants at home or at work, or will be returned by participants
visiting the clinical research facility. At the same time, participants will provide
a blood sample and have their anthropometric and blood pressure measurements taken.
They will also be asked to complete the same questionnaires previously completed at

After the follow-up assessments, participants will receive a personalised report with
feedback on their health status, levels of physical activity, fitness and sedentary
behaviour and information on how these have changed over time. If any of the assessments
indicate abnormalities, participants will be notified of their results by the study
clinician (SJG) in the first instance and then instructed to visit their general practitioner.

During phase III, all participants given sit-stand desks will be asked to complete
short weekly video and/or paper-based diaries to record the circumstances under which
they choose to use the desks to stand, as well as the barriers and facilitators to
standing. At random times, participants will also be directly observed in their workplaces
by a researcher to record their behaviour, including the different tasks undertaken
while standing vs sitting. The content of the diaries and the results from the observations
will be analysed to create a list of the possible factors that facilitate and inhibit
desk use. This information will be used in designing the main trial to maximise the
possibility of desk use.

Phase IV

Participants offered sit-stand desks will be interviewed about their experiences of
using sit-stand desks, in order to explore the circumstances under which they chose
to stand both at work and in other contexts; their attitudes towards standing in a
predominantly sitting environment, i.e. the workplace; and the acceptability of the
intervention and of the study procedures. Employer representatives will also be interviewed,
in order to explore the acceptability of sit-stand desks at the organisational level.
Interviews will be semi-structured and will last approximately 30 min. An interview
schedule will be designed based on the existing literature and in collaboration with
an expert qualitative researcher with experience in research within the field of physical
activity and public health. The interview schedule will be pre-piloted on a small
number of employees within the target organisation who currently use sit-stand desks.

Outcomes and measures

Phase I

The following outcomes will be assessed via an online questionnaire:

Proportion of eligible participants interested in taking part in a 3-month trial
on the use of sit-stand desks at work

Proportion of eligible participants interested in taking part in a 6-month trial
on the use of sit-stand desks at work

Demographic characteristics

° Age

° Gender


° Smoking status

° Salary band

° Highest educational qualification

° Position within company

Proportion of participants preferring desk mounts vs full desks

Proportion of participants preferring to be assessed at home vs work vs the clinical
research facility

Phase II

Proportion of workplaces suitable for use of full desks and desk mounts assessed
via workplace auditing and recording

Proportion of workspaces permitting participants’ choice of desk to be installed

Phase III

Practicalities of delivering the intervention, assessed by recording:

° The time lapse between ordering the desks from the manufacturer and their delivery

° Any permissions needed to install each desk type

° The feasibility of training research staff to install desks

° The feasibility of one person (a trained research assistant) installing each desk
without help

° The amount of time needed to install each desk

° Any problems associated with delivering the desks to participants

° Any problems installing each desk type

° The practicalities associated with removing existing desks (applicable only when
using full desks)

Circumstances and factors affecting desk use assessed via direct observations and

Proportion of participants dropping out between randomisation and the 3-month follow-up

Trial-related outcomes, assessed at baseline (before randomisation) and at 3-month

° Physical activity energy expenditure estimated via Actiheart3

° Sedentary behaviour measured using activPAL inclinometers4

Sitting time during (a) working hours (workplace sitting time) and (b) all waking
hours (total sitting time)

Sitting patterns (number of sit-to-stand transitions; sitting time accrued in prolonged
bouts (?30 min)) during (a) working hours (workplace sitting patterns) and (b) all
waking hours (total sitting patterns)

° Cardio-metabolic related outcomes:

BMI calculated from weight and height

Weight measured using a scale

Height measured using a stadiometer

Fat mass and fat-free mass measured via a spectroscopy device

Blood pressure, measured via an electronic monitor

Waist-hip circumference measured using a tape measure

Plasma total cholesterol, HDL, triglycerides and HbA1C, measured via non-fasting
blood tests

° Musculoskeletal discomfort measured using the Nordic Musculoskeletal Questionnaire

° Ability to work, work productivity, presenteeism, absenteeism and job satisfaction
measured using the Work ability index 81], the Stanford presenteeism scale 82] and Measure of job satisfaction 83]

° Domain-specific sedentary behaviour measured using the SIT-Q-7d, a domain-specific
last-7-day sedentary behaviour questionnaire 84]

° Health symptoms, including neck pain, headache, back pain, fatigue, eye strain
and loss of concentration, measured using a checklist

° Health-related quality of life measured using the Euro-Quality of Life 5 (EQ-5D-5L)

° Food and drink consumption measured using a daily food log

Phase IV

All outcomes assessed via qualitative interviews:

Experiences of using desks, including factors perceived as affecting desk use, issues
with desk use (contextual, practical, emotive or others) and adverse consequences
(work, health or otherwise related)

Experiences of other intervention components

Company representatives’ perceptions of using sit-stand desks

Acceptability of intervention

Acceptability of assessments and burden

Acceptability of study procedures

Other measures

Proportion of participants dropping out between phases

Data analysis

The main analysis of this study will include descriptive statistics of feasibility
and acceptability outcomes, including recruitment and attrition rates. We will also
calculate differences between the average change from baseline in energy expenditure
and sitting time between the intervention and control groups to estimate possible
effect sizes from which to power the main trial.

Analysis of the anonymised data gathered through the semi-structured interviews will
be conducted following the principles of the Framework method 41].

Research governance

The study is funded by a grant from the Department of Health Policy Research Program
(Policy Research Unit in Behaviour and Health [PR-UN-0409-10109], the Medical Research
Council [Unit Programme number MC_UU_12015/3] and the British Heart Foundation [Intermediate
Basic Science Research Fellowship grant FS/12/58/29709 to KW]. The funders have no
role in the study design, data collection or analysis; decision to publish; or preparation
of the manuscript. Ethical approval was obtained by the University of Cambridge Psychology
Department Research Ethics Committee (reference number PRE.2015.100; date of approval:
November 18, 2015). Management, data storage and analysis will be conducted at the
Behaviour and Health Research Unit, Primary Care Unit, Department of Public Health
and Primary Care, University of Cambridge.