Physical Workload and Work Capacity Across Occupational Groups
Condition: Occupational Rehabilitation; Professional Reintegration; Work Load; Work Capacity
Study type: Observational

Summary: 
      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.
    

Detailed description: 
      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%.
    

Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Healthy adult full-time employees
      
Keywords: Physical work requirements; Energy expenditure; Physical activity; Different occupational categories; Aerobic capacity