Work Load Clinical Trial
Official title:
Physical Workload and Work Capacity Across Occupational Groups
Background: Physical activity is defined as any bodily movement produced by skeletal muscles
resulting in energy expenditure (Caspersen, 1985). According to classical work physiology,
energy expenditure was considered as basis for assessing the severity of manual work
(Grandjean 1991). Steele et. al. found blue collar workers to report significantly more
walking activity, daily step counts and MET min/week than professionals and white collar
workers. However, the energy cost of physical activity may not necessarily be equivalent to
body movement. Therefore, modern concepts include also other aspects reflecting the amount
of workload. Soer et. al. applied an evaluation system consisting 12 work-related tests to
establish functional capacity in healthy employees. The assessment included various lifting
and energetic tasks as well as coordination exercises. In occupational rehabilitation a
balance between workload and work capacity is necessary for professional reintegration.
Thus, it is of great value to evaluate a wide range of work requirements across occupational
groups in terms of energy expenditure, physical activity and aerobic capacity.
Aim: The aim of this study is to examine the amount of physical activity and energy
expenditure during a normal working day with focus on differences between occupational
groups.
Method: To analyze the situation in Switzerland, 300 healthy and full-time employed adults
between 18-65 years will be investigated in the Basel region. Participants will be
stratified by occupational category according to the ISCO-88 and will then be merged into 3
groups with low-, moderate- and high-intensity occupational activity. By wearing the
SenseWear Mini Armband on 7 consecutive days, average daily energy expenditure, activity
duration at different intensities and step counts will be assessed during work-time. In
addition, individual's aerobic capacity will be determined by the 20-meter shuttle run test.
Outlook: This study is expected to provide detailed information about physical work
requirements with regard to professional reintegration. For developing adequate intervention
and treatment strategies, it is of great value to evaluate performance criteria across
occupational groups.
1. Introduction
1.1 Background
Regarding occupational rehabilitation, a balance between workload and individual's work
capacity is required for returning to work successfully after an injury or illness.
Therefore, it is of great value to evaluate a wide range of physical work requirements
and to assess employee's work capacity across occupational groups. Although several
approaches have been made in this regard, there are few objective data available so far
and no established reference values exist to evaluate, whether, when and how a return
to work is possible. One reason could be that objectifying workload and work capacity
is methodically challenging because of their multidimensional nature [1, 2].
Physical activity is defined as any bodily movement produced by skeletal muscles
resulting in energy expenditure [3]. In classical work physiology, energy expenditure
was therefore considered as basis for assessing the amount of workload [4, 5]. However,
the energy cost of physical activity may not necessarily be equivalent to body movement
[6]. For that reason, modern concepts include also other aspects reflecting the
severity of manual work. The 'Dictionary of Occupational Titles' (DOT), developed by
the U.S. government, classifies professions into five categories (sedentary, light,
medium, heavy, very heavy) based on the amount of energy expended as well as on the
intensity and duration of lifting or carrying during work [7]. Though, the DOT
classification has not been based on quantitative work-related analyses, but rather on
consensus meetings of experts. Furthermore, its validity has not been established.
Work capacity can be assessed using functional capacity evaluations (FCEs), which
measure the ability of subjects to perform specific activities [8]. Worldwide, there
are various FCE protocols available being job specific [9], pathology specific [10, 11]
or of a more general type. Soer et al. applied an evaluation system consisting of 12
work-related tests to establish functional capacity in healthy employees [12]. The
assessment included various lifting and energetic exercises as well as coordination
tasks. From the test results, normative FCE values were acquired for each DOT-category,
which can be compared to patient data in order to make work recommendations.
However, since validity of the DOT has not been proved, further analysis concerning
workload assessment is required. Moreover, the application of such complex FCE tools is
related to high expenses and efforts and may therefore not be appropriate in a general
clinical or field context. Especially in large populations, implementing highly
accurate instruments is difficult due to high costs and poor practicability [13].
For these reasons, the present study will focus on workload by investigating a wide
range of physical work requirements across occupational groups and putting them in
relation to employees' aerobic capacity. Since physical activity is characterized by
various dimensions, such as duration and intensity [3], these factors will be
considered for a comprehensive analysis.
1.2 Specific aims
The primary aim of this study is to investigate healthy employees in Switzerland
regarding energy expenditure, metabolic equivalents (METs), physical activity duration
at different intensities and the number of steps taken during a normal working day with
focus on differences between occupational groups. Furthermore, the association between
physical activity and aerobic capacity will be examined.
1.3 Hypotheses
1.3.1 Individuals practising heavy work are more physically active and consume more
energy than those with light work.
1.3.2 Aerobic capacity (VO2max) correlates positively with work and non-work related
physical activity.
1.4 Potential significance
This study is expected to provide detailed information about physical work requirements
and performance criteria of different occupational groups. This may be valuable
regarding treatment and professional reintegration after an injury or illness, since up
to now no established reference values exist. Objective workload data might improve
intervention strategies and clinicians' recommendations for a successful return to
work.
2. Methods
2.1 Study design
2.1.1 Primary and secondary outcomes
Our primary objective is to analyze work related physical activity parameters measured
by the SenseWear Mini armband and aerobic capacity determined by the 20-meter shuttle
run test across occupational groups. Furthermore, perceived work intensity, activity
behaviour in recreation, quality of life, body composition and several personal- and
job-related factors will be investigated as secondary outcomes.
2.1.2 Study procedures
In this cross-sectional study, we plan to recruit healthy and full-time employed adults
from different occupational fields in the Basel region, Switzerland. It is intended to
start with a pilot study in January 2013, in which a total of 15 persons will be
examined.
Recruitment will initiate in May 2013 and will end as soon as 300 individuals are
included in the study.
Potential subjects will be contacted and asked for study participation by phone or by
mail. Willing individuals meeting the inclusion criteria will fill out the informed
consent form before starting the measurement procedure.
At the first study visit, body measurements will be carried out such as height, weight
and waist circumference (WC) and body mass index (BMI) will be calculated. In addition,
a variety of personal- and job-related factors will be recorded. Furthermore, subjects
will perform a 20-meter shuttle run in order to measure aerobic capacity.
During the subsequent week, participants will be instructed to document their daily
work activities and to rate their work related physical exertion twice per day using
the Borg Scale. Moreover, by wearing the SenseWear Mini armband on seven consecutive
days, physical activity and energy expenditure will be objectified.
One week later at the second study visit, all subjects will complete several
self-administered questionnaires concerning work and non-work related physical activity
behaviour (IPAQ), health-related quality of life (SF-36) and self-assessment of
professional activity and its intensity (VAS). In addition, open questions will be
asked to each participant about past-week physical exertion in comparison to a normal
week.
The time required for the two study visits taking place at the individual's
workstation, will be around 90 minutes per person. In addition, every participant will
wear the activity monitor on seven consecutive days.
Termination criteria for the measurements are skin irritations caused by the SenseWear
Mini armband and exertional dyspnea during 20-meter shuttle run.
2.2 Selection of study participants
2.2.1 Recruitment
In this study, it is intended to recruit 300 subjects from different occupational
groups with low-, moderate- and high-intensity occupational activity, which are defined
in a later section (see chapter 2.3.2). Based on this classification, companies will be
selected. In each occupational group, 100 participants will be enrolled. Furthermore,
homogeneity of age and gender within each group will be aimed at recruiting.
First, we will contact the management of potential enterprises in order to present our
project. If they are interested in a collaboration, we will ask for contact details of
potentially recruitable employees, who will then be addressed by a member of our
research team. Individuals will be informed and asked for study participation by phone
or by email. Furthermore, it is planned to distribute study flyers in the companies, so
that interested employees have the opportunity to contact us directly. In both
situations, the recruitment and information process will be done externally.
2.2.2 Inclusion criteria
Healthy and full-time employed individuals between the age of 18 and 65, who have a
sufficient knowledge of the German language in order to fill in the self-administered
questionnaires by themselves.
2.2.3 Exclusion criteria
Subjects not giving consent for participation as well as those with movement
restrictions, various diseases and accidents within the last three months that affect
productivity at the workplace, cannot take part in this study. Furthermore, night shift
workers will be excluded from participation.
2.3 Instruments
2.3.1 Personal- and job-related factors
For each subject, gender (male / female) and employment (temporary / permanent) will be
assessed as binary variables. Nationality (Swiss / EU / other), marital status (single
/ married / divorced) and smoking status (yes / no / never) will be recorded with three
categories, while alcohol consumption (never / once to several times per month / once
to several times per week / once per day), German skills (very good / good / medium /
bad / very bad), highest education (compulsory school / apprenticeship / higher
vocational school / diploma or maturity / university) and working time model (flextime
/ fix time / shift work / weekend work) will be evaluated with four, five and six
categories, respectively. Age, native language, profession, avocation, medication,
illnesses, accidents and working hours will be asked as open questions. Furthermore, to
get an overview of the individual work activity, participants will be asked to keep a
daily list of the main completed tasks including time information in accordance with
the questionnaire regarding professional integration and pension [14].
2.3.2 Classification of occupations
The reported professions will be classified into 9 categories based on the
International Standard Classification of Occupations ISCO-88 [15] (1. Managers, 2.
Scientists, 3. Technicians, 4. Office workers, 5. Service workers, 6. Agricultural
workers, 7. Craftsmen, 8. Machine operators, 9. Labourers). These 9 categories will
then be collapsed into 3 groups with low-, moderate-and high-intensity occupational
activity according to Suva experts in the field of ergonomics (1st group: Categories 1
(Managers), 2 (Scientists) and 4 (Office workers); 2nd group: Categories 3
(Technicians), 5 (Service workers) and 8 (Machine operators); 3rd group: Categories 6
(Agricultural workers), 7 (Craftsmen) and 9 (Labourers). Reliability of this
stratification has been previously shown [16, 17].
2.3.3 International Physical Activity Questionnaire
The International Physical Activity Questionnaire (IPAQ) represents a convenient and
simple instrument for measuring health enhancing physical activity at the population
level. The self-administered long version of the IPAQ, being freely available in
internet [18], will be used in the present study. It includes 26 questions and assesses
past-week frequency (days) and duration (time per day) of physical activity within the
domains of work, leisure-time, transport, domestic and garden. Moreover, each domain
consists of walking, moderate and vigorous activities.
According to the IPAQ guidelines for data analysis [19], continuous scores in form of
MET-minutes per week will be calculated for each domain. MET-minutes per week, defined
as energy costs of physical activity, will be computed by multiplying the intensity
(specific MET value) of an activity with its frequency (days) and duration (minutes).
The corresponding MET values are set by the IPAQ guidelines based on the compendium of
physical activity [20].
According to numerous validity and reliability tests carried out in twelve different
countries, the IPAQ is considered as an internationally valid assessment tool with
acceptable measurement properties [21]. The long version of the IPAQ was translated
into German as part of a dissertation and was validated in an Austrian sample [22]. It
could be shown that it is suitable for research purposes with regard to physical
activity detection [23].
2.3.4 SF-36
The SF-36 is a general quality of life questionnaire consisting of 36 items, which are
formatted as binary questions or as semantic six-point differential scales. It refers
to the past four weeks and includes nine content areas concerning vitality, general
health perception, physical functioning, social functioning, role limitations
(emotional/physical problems), pain, mental health and health change [24]. The SF-36 is
considered to be the gold standard for measuring functional status and health-related
quality of life and is therefore the most used questionnaire in this context [25].
Since physical and mental disorders as well as pain may influence activity behaviour,
the SF-36 will be used in the present study to adjust for potential confounders.
2.3.5 Visual Analogue Scale
The Visual Analogue Scale (VAS) is a measuring instrument for subjective
characteristics that cannot be directly measured. Individuals express their response to
a VAS item by marking a position along a continuous line between two end-points.
The indicated locus will then be quantified by a defined scale [26]. In epidemiologic
and clinical research, the most common VAS is a straight horizontal line of 100 mm
length with its ends representing extreme limits of the measured parameter (worst -
best) [27]. The VAS score is determined by measuring the distance in mm from the left
end of the line to the point marked by the participant. Validity and reliability of VAS
have been scientifically tested for a variety of parameters, such as acute and chronic
pain [28, 29].
In this study, individual's perception of past-week work and non-work related physical
exertion and effort will be assessed by 100mm VASs. This may be valuable to evaluate
whether the investigated period (exposure time) is representative and reflects a normal
week.
2.3.6 Borg Scale
The Borg Scale represents a simple method to rate perceived exertion and can be
compared to other scales, such as VAS. It is used for various purposes, such as
measuring patient's exertion during a performance test or assessing the intensity of
training and competition in athletes [30].
The original scale developed by Borg ranging from 6 (no exertion at all) to 20 (maximal
exertion) was updated and transformed into a combined category-ratio scale CR10 with
the ratings 0 (nothing at all) to 10 (very very hard) [31, 32].
The latter will be used in the present study. Subjects will be instructed to rate their
work related physical exertion twice per day, at the end of the morning and in the late
afternoon. The indicated Borg value should reflect how heavy and strenuous work feels
to them considering all sensations of physical stress, effort and fatigue.
2.4 Measurements
2.4.1 Anthropometric measurements
Anthropometric measurements include body height, body weight and waist circumference.
Body height will be assessed without shoes by a medical measuring stick to the nearest
mm. The measurement of body weight will be performed on subjects in light clothing
without shoes by a medical scale with an accuracy of 0.1 kg.
Waist circumference will be determined midway between the lowest rib and the iliac
crest according to the Swiss Heart Foundation using a medical measuring tape with a
precision of 0.1 cm. The measurement will be carried out on standing subjects after a
moderate expiration.
2.4.2 20-meter shuttle run
The multistage 20-meter shuttle run is a common endurance fitness test to evaluate the
maximal aerobic power of healthy adults [33]. It is simple in use and economical and
large groups can be tested at once.
This test will be conducted on a flat, non-slip surface and participants will be
instructed to run back and forth between two lines, which are 20 meters apart (Figure
1). Running velocity is determined by intervals between two audio signals emitted by a
pre-recorded tape. Subjects have to touch the 20 meter lines simultaneously with the
sound of these signals. The initial running velocity is 8.5 km/h. Every minute (stage),
the intervals are shortened and speed is increased by 0.5 km/h. The test ends when the
subject gives up or when he can no longer keep the pace and does not reach the line in
time (> 3 metre away from the 20 meter line) twice in a row.
The test result corresponds to the number of reached stages. According to a validated
table [34], this score is used to predict maximal oxygen uptake (VO2max), which can be
compared to age-dependent normative data for males and females.
Validity of the 1 minute stage version of the 20-meter shuttle run to predict VO2max in
adults was established by Léger et al. [35], who compared the maximal shuttle run speed
to VO2max attained during a multistage treadmill test.
In addition, blood pressure and oxygen saturation will be assessed prior to testing in
order to detect potential contraindications. Resting pulse and recovery pulse (2
minutes after test) will be measured and heart rate will be continuously recorded
during test. Furthermore, participants will be instructed to rate their perceived
physical exertion before and after test using the Borg scale.
2.4.3 SenseWear Mini armband
The SenseWear Mini armband is a small, lightweight and wireless multisensory activity
monitor developed by Bodymedia (Pittsburgh, Pennsylvania, USA), which integrates motion
data from a three-axis accelerometer along with several other physiological sensors
such as heat flux, skin temperature and galvanic skin response. Validity was
established by Johannsen et al. [36] comparing energy expenditure estimates of the
SenseWear Mini armband against the criterion method 'Doubly-Labeled-Water' in healthy
adults.
The subjects will be instructed to wear the SenseWear Mini armband on the upper left
arm (triceps area) for 7 consecutive days, including while sleeping, with the exception
of one hour daily spent on personal hygiene (23 hours per day). Reliability of this
assessment period has been previously shown [37].
For recording non-wearing periods, such as water activities and showers, participants
will be asked to keep a diary. The physiological data collected by the armband's
sensors will be processed by specific algorithms (professional software V.7.0,
algorithm V.2.2.4) to calculate participants' daily energy expenditure, METs, physical
activity duration at different intensities and the number of steps. Gender, age,
height, weight, smoking status and handedness will also be considered in these
calculations.
2.5 Statistical analysis
Statistical analyses will be done using the software R (version 2.15.1) and IBM SPSS
Statistics (version 19.0). Statistical significance will be acquired if a p value of
less than 0.05 is attained.
Data will be presented by descriptive statistics within occupational groups. Cross
tables are reported as counts and percentages. Ordinal variables are reported as median
and Interquartile range (IQR). Metric variables are reported as mean and standard
deviation (SD).
To evaluate primary endpoints, linear regressions will be performed. Independent
variable is "occupational group", dependent variables are "average daily active energy
expenditure", "average daily physical activity duration" and "average daily number of
steps". Optionally, personal and job related factors can be included in the regression
analyses as covariates. If appropriate, data will be log-transformed. Regression
results will be presented as differences of means between "occupational categories"
with corresponding 95% confidence intervals (C.I.) and p-values. In case of logarithmic
distributed data, geometric mean ratios will be presented.
To evaluate secondary endpoints, linear regressions will be conducted. In case of
ordinal variables, non-parametric methods will be applied.
Furthermore, the mean and individual time courses of physical activity periods will be
plotted for all primary and secondary variables.
2.6 Sample-size calculation
Since "average daily active energy expenditure" measured by the SenseWear Mini armband
represents a valid and reliable parameter, it is considered to be the most important
primary endpoint of the present investigation. For this reason, only this variable is
subject to a power calculation. In a previous study, the SD of "average daily active
energy expenditure" during a normal work shift was found to be 730 kcal [38]. The
expected mean difference between the three occupational groups will be around 500 kcal.
Assuming a sample size of 100 subjects in each occupational group, there is a power of
>90% to detect a mean difference of 500 kcal between any of these groups. This
calculation is based on the assumption of a within group SD of 730 kcal and on a
two-sided significance level of 5%.
;
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