Relationships between physical activity, work ability, and health-related quality-of-life : A cross-sectional study among young adult men in Finland

(1)

Department of Orthopaedics and Traumatology Doctoral Program in Clinical Research

Faculty of Medicine University of Helsinki

Finland

RELATIONSHIPS BETWEEN PHYSICAL ACTIVITY, WORK ABILITY, AND HEALTH-

RELATED QUALITY-OF-LIFE

A CROSS-SECTIONAL STUDY AMONG YOUNG ADULT MEN IN FINLAND

Ville Päivärinne

DOCTORAL DISSERTATION

To be presented for public discussion with the permission of Faculty of Medicine of the University of Helsinki, in Auditorium I of Töölö Hospital, on the 14th of

January 2022 at 12 o’clock.

Helsinki 2021

(2)

Supervisors

Professor Emeritus Ilkka Kiviranta, M.D., Ph.D.

Department of Orthopaedics and Traumatology Clinicum

Faculty of Medicine University of Helsinki Finland

Professor Ari Heinonen, Ph.D.

Faculty of Sport and Health Sciences University of Jyväskylä

Finland Reviewers

Professor Karen Søgaard, Ph.D.

Department of Sport Science and Clinical Biomechanics University of Southern Denmark

Denmark

Professor Mikel Izquierdo, Ph.D.

Department of Health Sciences Public University of Navarra Spain

Opponent

Professor Andreas Holtermann, Ph.D.

National Research Centre for the Working Environment Copenhagen

Denmark

The Faculty of Medicine uses the Urkund system (plagiarism recognition) to examine all doctoral dissertations.

ISBN 978-951-51-7788-9 (pbk.) ISBN 978-951-51-7789-6 (PDF)

(3)

ABSTRACT

Although the positive health benefits of physical activity (PA) are well established, most of the evidence is linked with one of the sub-domains of PA, which is leisure-time physical activity (LTPA). The other domains besides LTPA (performed during free time) are occupational physical activity (OPA) (performed while working), transportation physical activity (TPA) (purpose to go somewhere), household physical activity (HPA) (engaging in housework), and sitting (such as while at work, at home, or studying). The role of the different domains of PA and their relations to different indicators of health or functioning, such as health-related quality-of-life (HRQoL) and work ability, have been minimally examined and are poorly understood.

The aim of this study was to examine how different sub-domains of PA relate to HRQoL or work ability in different work requirements among the Finnish male population between 20 and 40 years of age. Data were obtained from 5000 male participants (born in 1969, 1974, 1979, 1984, or 1989) that were randomly selected from the population register as a population sample.

Self-reported questions and questionnaires were used in the studies. Study I explored the relationships between sub-domains of PA and HRQoL (n = 1425).

Study II explored the relationships between LTPA and work ability in different OPA levels (n = 921). Study III examined the relations between LTPA and work ability in different work requirements among workers with or without current depressive symptoms (n = 921). Study IV examined the relationships between different sub-domains of PA and work ability with perceived physical or mental demands of work (n = 921).

Out of all domains of PA, LTPA was the only one that was positively related to mental and physical aspects of HRQoL or work ability. Furthermore, the results indicate that different domains were related differently between physical or mental aspects of HRQoL. More accurately, relatively high LTPA was related to better quality-of-life in both mental and physical aspects of HRQoL, whereas OPA was negatively related to physical health indicators and higher daily sitting was negatively related to mental-health indicators.

Moreover, this study indicates the importance of LTPA among workers, particularly those with higher work-related physical strain, to endure the demands of daily work chores. Although the results of this study indicate that higher LTPA is related to better work ability in workers without depressive symptoms, the workers with depressive symptoms may need more than exercise to improve work ability, particularly if their job description included higher physical or mental demands. In addition, the findings reveal that regardless of whether the work is mainly physical or mental, LTPA could possibly compensate for the negative relations associated with lower work ability.

(4)

The results of this study add useful information to the body of evidence between domain-specific PA and work ability or HRQoL. Moreover, the results provide important health implications for the positive effects of LTPA particularly among workers that engage in heavy physical labor. Additionally, these results provide information about the interaction between different levels of LTPA and OPA or perceived demands of work among adult workers with or without current depressive symptoms. Future research should examine the relationships between PA and work ability, HRQoL, or health in general with longitudinal study designs and with assessment methods that measure PA simultaneously through objective and subjective techniques.

(5)

TIIVISTELMÄ

Tutkimusnäyttöä fyysisen aktiivisuuden (physical activity, PA) terveyttä edistävistä ja ylläpitävistä hyödyistä on runsaasti, mutta suurin osa näytöstä liittyy vapaa-ajalla tapahtuvan fyysisen aktiivisuuden (leisure-time physical activity, LTPA) mittaamiseen. Muita PA:n osa-alueita ovat työssä (occupational physical acitivity, OPA), siirtymisissä (transportation physical activity, TPA) ja kotitaloustöissä tapahtuva fyysinen aktiivisuus (household physical activity (HPA). PA:n osa-alueiden roolia ja suhdetta erilaisiin terveyden tai toiminnan indikaattoreihin, kuten terveyteen liittyvään elämänlaatuun (health-related quality of life, HRQoL) ja työkykyyn on tutkittu vähemmän, minkä vuoksi näitä yhteyksiä tunnetaan myös heikommin.

Tämän tutkimuksen tavoitteena oli tutkia miten 20-40-vuotiailla suomalaisilla miehillä PA:n eri osa-alueet vaikuttavat elämänlaatuun tai työkykyyn työn eri kuormituksissa. Tutkimusaineistona oli väestörekisteristä satunnaisotannalla valitut 5000 miehestä, jotka jaettiin 1000 miehen ikäkohortteihin syntymävuosien (1969, 1974, 1979, 1984 ja 1989) mukaan.

Tutkittavien liikunnallista aktiviteettia, työkykyä ja henkilökohtaisia taustatietoja selvitettiin kyselylomaketutkimuksella. Osatyössä I tutkittiin PA:n, istumisen ja HRQoL:n välisiä suhteita (n=1425). Osatyössä II tutkittiin LTPA:n ja työkyvyn välisiä suhteita OPA:n eri tasoilla (n=921). Osatyössä III tutkittiin LTPA:n ja työkyvyn suhdetta työn eri kuormituksissa työntekijöillä, joilla joko oli tai ei ollut masennusoireita (n=921). Osatyössä IV tutkittiin PA:n eri osa-alueita ja niiden yhteyttä työkykyyn sekä työssä koettuja fyysisiä tai henkisiä vaatimuksia (n=921).

Kaikista PA:n osa-alueista LTPA oli ainoa, jolla oli positiivinen yhteys HRQoL:n tai työkyvyn henkisiin ja fyysisiin osatekijöihin. Tarkemmin ilmaistuna suhteellisen korkealla LTPA:lla oli yhteys parempaan elämänlaatuun HRQoL:n henkisissä ja fyysisissä osatekijöissä, kun taas OPA:lla oli negatiivinen yhteys HRQoL:n fyysisen terveyden indikaattoreihin.

Lisäksi korkeampi päivittäinen istumisaika yhdistyi negatiivisesti HRQoL:n henkisen terveyden indikaattoreihin. Tutkimuksen tulokset korostavat LTPA:n tärkeyttä, etenkin työntekijöillä, joiden työ on fyysisesti raskasta.

Tulokset myös osoittavat, että korkeammalla LTPA:lla oli mahdollisesti yhteys parempaan työkykyyn henkilöillä, joilla ei ollut masennusoireita, mutta masennusoireista kärsivät saattavat tarvita muutakin kuin liikuntaa työkyvyn parantamiseksi, etenkin jos heidän työnkuvaansa sisältyi reilusti fyysisiä tai henkisiä vaatimuksia. Lisäksi tulokset osoittavat, että riippumatta siitä, oliko työ enemmän fyysistä tai henkistä, korkeampi LTPA mahdollisesti vähentää huonommasta työkyvystä aiheutuvia negatiivisia assosiaatioita.

Tämän tutkimuksen tulokset tarjoavat lisää tietoa LTPA:n aiheuttamista myönteisistä terveysvaikutuksista sekä LTPA:n, OPA:n, depression oireiden tai työn luonteen yhteisvaikutuksista työkykyyn.

Jatkossa tulisi tutkia PA:n ja työkyvyn, HRQoL:n tai terveyden välisiä suhteita pitkittäisotannalla ja arviointimenetelmillä, jotka mittaavat PA:ta samanaikaisesti objektiivisten ja subjektiivisten menetelmien avulla.

(6)

ACKNOWLEDGEMENTS

This study was carried out in the Orthopaedic Research Group, Department of Orthopaedics and Traumatology and Doctoral Program of Clinical Research, Faculty of Medicine, University of Helsinki, and Helsinki University Hospital between the years of 2017 and 2021.

This thesis was financially supported by the Finnish Cultural Foundation (Ester and Uuno Kokki Fund; ref: 00180887, Kymenlaakso Regional Fund;

Olavi and Alli Pietikäinen; ref: 35171923, Hilda Laasonen Fund; ref:

00210894), Social Insurance Institute of Finland (ref: 16/26/2009), Scientific Advisory Board for Defence (ref: 630/70.03.01/2015, 474/70.03.00/2016, 50/70.03.01/2018), State Research Funding, and Centre for Military Medicine. I am grateful for this financial support.

I want to express my sincere gratitude to my supervisors Professor Emeritus Ilkka Kiviranta and Professor Ari Heinonen for the great opportunity to work with this project, and all the support, encouragement and freedom I have received from you. I would like to thank Ari for introducing me into the complex world of research during my master’s degree at the University of Jyväskylä. Furthermore, I want to thank you for helping me to pursue my academic career in PhD studies. I would like to thank Ilkka for offering me a fantastic opportunity to pursue my doctoral studies at the Faculty of Medicine.

Thank you for trusting me with the doctoral and other projects, allowing me the chance to develop my academic skills and becoming a better researcher. In addition, I am grateful to you both for offering me the guidance and being supportive during this journey. I would like to thank Hannu Kautiainen for being a great mentor with the statistical methods section of my thesis. You have helped me tremendously with your knowledge and insight. I am grateful for the opportunity to work with you. Thank you.

The pre-examiners Professors Karen Søgaard and Mikel Izquierdo are truly appreciated for their critical review and valuable feedback of this thesis. My thesis improved substantially due to your insightful comments and suggestions. I thank Professor Andreas Holtermann for kindly agreeing to be my opponent. Thank you Professor Teppo Järvinen for accepting the role of Custos.

I would like to warmly thank all my co-authors: Professors Jari Arokoski and Hannu Koponen, and MD Marie Thodén. I am also grateful for thesis committee members, Professor Hannu Koponen and Docent Harri Pihlajamäki for your involvement during these years.

I also want to thank PhD Aki Rintala, PhD Petri Wiklund and PhD Eve Salonius for offering me valuable peer support in order to figure out problems or questions that occurred during this winding road. Aki, our conversations and the personal support I received from you were extremely valuable. Thank you so much.

(7)

Thank you to my parents Tiina and Juha and to my sister Kirsi for all their support throughout the years. Without it, I would not have gotten this far.

Thank you for believing in me.

Dear Susanne, I love you. You are the main reason I was able to finish this project. Thank you for your love and support. Thank you for being in my life.

Furthermore, thank you for our son, Viljam. You both mean the world to me.

Viljam, thank you for everything.

Helsinki, December 2021 Ville Päivärinne

(8)

LIST OF ORIGINAL PUBLICATIONS

This thesis is based on the following publications:

I Päivärinne, V., Kautiainen H., Heinonen A. and Kiviranta I.

(2018), Relations between subdomains of physical activity, sedentary lifestyle, and quality of life in young adult men.

Scandinavian Journal of Medicine & Science in Sports, 28 (4):

1389-1396.

II Päivärinne, V., Kautiainen H., Heinonen A. and Kiviranta I.

(2019), Relationships of leisure-time physical activity and work ability between different occupational physical demands in adult working men. International Archives of Occupational and Environmental Health, 92 (5): 739-746.

III Päivärinne V., Thodén M., Kautiainen H., Arokoski J., Koponen H., Heinonen A. and Kiviranta I. (2020), Physical activity and ability to meet different work requirements among adult working men with or without current depressive symptoms.

International Archives of Occupational and Environmental Health. https://doi.org./10.1007/s00420-020-01595-6.

IV Päivärinne V., Kautiainen H., Heinonen A., Kiviranta I. (2021) Different sub-domains of physical activity and their relations to work ability between physical or mental aspects of work – a cross-sectional study of Finnish adult men.

The publications are referred to in the text by their Roman numerals.

The original publications are reprinted with the permission of the copyright holders.

(12)

ABBREVATIONS

β beta coefficient BDI beck depression inventory

BMI body mass index

BTH equal amount of physical and mental work

CI confidence interval

CV cardiovascular

HPA household physical activity HRQoL health-related quality-of-life

IPAQ international physical activity questionnaire

IQR interquartile range

LTPA leisure-time physical activity

MCS mental component summary of SF-36

MENT mental work

MET metabolic equivalent of task NRS numeric rating scale

OPA occupational physical activity

O2 oxygen

PA physical activity

PCS physical component summary of SF-36

PHYS physical work

RCT randomized controlled trial SD standard deviation of mean

SF-36 36-item short form survey TPA transportation physical activity VO2max maximal oxygen uptake YOB year of birth

WAI work ability index

WHO World Health Organization

(13)

1 INTRODUCTION

Physical inactivity and increasingly sedentary lifestyles have become major global public health problems and are associated with 6-10% of the major non- communicable diseases, such as coronary heart disease, type 2 diabetes, and breast and colon cancers. Physical inactivity and sedentary lifestyles are also associated with reduced life expectancy(1). In 2013, physical inactivity, due to its association with risk of disease incidence and mortality, was responsible for a total cost of $67.5 billion; a major burden was concentrated in the public sector(2). Conversely, the health benefits of physical activity (PA) are well established and the benefits include lower risk of diabetes, hypertension, cardiovascular disease, and breast and colon cancer(3). In addition, PA can help maintain a healthy weight, has positive effects on mental health or health- related quality-of-life (HRQoL), and delays the onset of dementia(3,4).

In general, PA can be defined as any bodily movement created by skeletal muscles that produces energy expenditure during different intensities(5).

Moreover, these intensities can be measured in the form of the metabolic equivalent of task (MET)(6). The human organism can adapt to an extensive variety of metabolic demands, for example imposed by exercise or work(7). In addition, the concept of PA is divided into the following five different sub- domains depending on the context of the PA: leisure-time physical activity (LTPA), occupational physical activity (OPA), household physical activity (HPA), transportation physical activity (TPA), and sedentary behavior.

Overall, PA as a whole is encouraged for the general population, and recent guidelines for adults recommend at least 150 minutes a week of moderate- intensity PA or at least 75 minutes a week of vigorous-intensity PA(6).

Although PA is highly emphasized in health promotion and disease prevention, most of the epidemiologic evidence lands under the domain of LTPA(8).

Possibly due to the strong evidence of LTPA compared to other domains, there is a common assumption across the guidelines that more PA is better regardless of the context, domain, or environment(5). However, recent evidence has suggested that work-related physical activity (or occupational physical activity [OPA]) could actually be detrimental to the health of the adult working population(5,9). Furthermore, although there are still occupations and job descriptions in western society that include high amounts of OPA, in recent years heavy physical labor has accompanied occupations that include low levels of PA or sedentary work(7).

Overweight and obesity accompanied with work-related fatigue and burnout are associated with lower work ability in the general working population, particularly among individuals with mainly sedentary work(10).

Conversely, high OPA is associated with lower work ability, musculoskeletal and cardiovascular disorders, and a higher mortality rate(11-14). Work ability relates to a worker’s physical and mental capacities and the demands of the job and can be used as a tool for disease and injury prevention and health promotion(15).

(14)

The Finnish population has the sixth longest working careers inside of European Union(16). However, to maintain or to improve this longevity, there is a need to equally improve the individual’s work ability, health, and well- being at work(16). Moreover, further evidence is needed to investigate the relationships between different PA domains and HRQoL or depressive symptoms. This study sought to examine the relations between PA and different indicators, such as HRQoL and work ability. The main focus was to examine how the sub-domains of PA and LTPA in particular relate to mental and physical functioning or work ability in different work requirements in Finnish adult men between 20 to 40 years old.

(15)

2 REVIEW OF THE LITERATURE

2.1 CONCEPT AND DOMAINS OF PHYSICAL ACTIVITY

2.1.1 PHYSICAL ACTIVITY

It has been theorized that during human evolution, physical activity (PA) and physical fitness have greatly influenced the evolutionary history of Homo sapiens as a means to develop the different physical attributes necessary for survival(7). However, over the past century, significant changes in the lives of people in industrialized countries have diminished the need to engage in strenuous PA(7). In fact, with increased physical inactivity and associated detrimental health effects, PA has become an important part of a healthy lifestyle(7). Physical activity can be defined as any bodily movement created by the skeletal muscles that produces energy expenditure(5). Other physical functions that require energy are breathing, circulating blood, or digesting food(7). The human organism can adapt to an extensive variety of metabolic demands, such as those imposed by work or exercise(7). Furthermore, PA consists of a wide variety of activities, movements, and postures(5). PA can be viewed as complex behavior that is categorized as willful or compulsory movement and is the only discretionary component of total daily energy expenditure(6,7,17). Moreover, PA encompasses all types, domains, and subdivisions of intensities, such as light, moderate, or vigorous activities. The intensities can also be divided into very light, light, moderate, hard, very hard, and maximal (6,7,17). Overall, PA is used as an umbrella term for leisure, domestic, transportation, and work-related activities. Exercise is considered a subset of PA that is more specifically designed to improve cardiorespiratory fitness, strength or power, cognitive function, and flexibility balance(18).

The energy expenditure associated with PA or exercise is viewed as the only discretionary component of total daily energy expenditure. Energy expenditure of activity in a sedentary person is typically only approximately 25% of total daily energy expenditure, whereas the energy expenditure high vigorous activity exercise or heavy labor may be as high as 50% of total daily energy expenditure(7). During different activities, oxygen consumption increases, the heart increases stroke volume, blood flow through muscles increase when skeletal muscle arterioles dilate, and mean arterial blood pressure increases slightly. Furthermore, the magnitude of these incidences depends on the intensity of the activity(19). In addition, these intensities can be measured in the form of metabolic equivalent of task (MET), kilocalories, joules, or oxygen consumption(6). Figure 2 illustrates the power output in METs throughout different categories of exercise intensity for two individuals, one with maximal oxygen uptake (VO2max) of 10 METs (equivalent to 10 times the resting expenditure) and the other with a VO2max of 5 METS, (possibly indicative of an elderly individual)(7). In this study, MET will be used as a unit to describe the intensity of different activities.

(16)

Figure 1. Two different examples of exercise intensity according to level of fitness, expressed as metabolic equivalent of task (MET). VO2max = maximal oxygen uptake. Modified from Bouchard et al. (7)

2.1.2 METABOLIC EQUIVALENT OF TASK DURING DIFFERENT INTENSITIES

Oxygen (O2) consumption is a measure of cellular respiration. It is usually measured in liters of oxygen consumed per minute and is related to exercise intensity (Figure 2)(19). One MET is defined as the amount of oxygen is consumed while sitting quietly or at rest, and is equal to 3.5 ml O2 per kg body weight × min (Table 1)(20). Furthermore, sedentary behavior is categorized as one of the core terms of PA that does not involve more than 1.5 METs and includes activities such as sitting, reclining, or lying(21). Most office work, driving a car, and sitting while watching television are considered as sedentary behaviors(6). Activity at 2 METs requires twice the resting metabolism (7.0 ml O2/kg/min) and 3 METs requires three times the resting metabolism (10.5 ml O2/kg/min), and so forth(20). Light-intensity PA requires more than 1.6 but less than 3.0 METs, and includes activities such as walking at a slow or leisurely pace or light standing chores. Moderate-intensity PA requires 3.0 to less than 6.0 METs and includes activities such as brisk walking or vacuuming.

Vigorous-intensity PA requires 6.0 or greater METs and includes activities such as running or carrying heavy loads up a flight of stairs(6).

(17)

Figure 2 Oxygen (O2) consumption during exercise. Modified from Silverthorn(19).

Table 1 Examples of sedentary, light, moderate, and vigorous physical activity in different categories of metabolic equivalent tasks (METs). Modified from Holtermann & Stamatakis(22) and Harvard Public Health(23).

Sedentary + standing

≤1.0 to ≤1.5

Light

<1.5 to <3.0

Moderate

≤3.0 to 6.0

Vigorous

≥6.0 Examples

of physical activities

Lying Walking – slowly Walking – very brisk (4-7 km/h)

Walking/hiking

Sitting quietly – watching TV

Sitting – operating heavy machinery

Cleaning – heavy (vacuuming)

Jogging at 10 km/h

Car driving Standing – light work (cooking, washing

dishes)

Mowing lawn Shoveling

Standing – computer work

Fishing – sitting Bicycling – light effort (16 km/h)

Carrying heavy loads

Playing most instruments

Tennis – doubles Bicycling fast (25 km/h) Tennis – singles

In general, PA is widely encouraged for the general population. Recent guidelines for adults recommend at least 150 minutes a week of moderate- intensity PA or at least 75 minutes a week of vigorous-intensity PA(6). The role of PA is highly emphasized particularly in health promotion, disease prevention, treatment, and rehabilitation(8). Additionally, moderate-to- vigorous PA has the strongest evidence of positive health effects, but recent studies have also shown positive effects of light-intensity PA(5,24). However, PA is complex and encompasses dimensions and subdomains such as occupational, leisure-time, transport, and household-related activity(25).

Moreover, the epidemiological evidence for beneficial health effects of PA is well documented, but it is mostly limited to PA during leisure time (26).

(18)

2.1.3 DOMAINS OF PHYSICAL ACTIVITY

Leisure-time physical activity (LTPA) occurs when individual is not working, transporting to a different location, or doing household chores (Table 2)(6).

LTPA is selected based on personal interests and needs(7). Examples of LTPA are sports or exercise, going for a walk, and playing games(6). Exercise is a form of LTPA that is performed repeatedly as training with a specific objective, such as improvement of physical performance, physical fitness, or health(7).

Moreover, LTPA in general is often performed over relatively short time periods, includes correct body postures and dynamic movements, and has determined rest and recovery periods(5). In addition, engaging in regular LTPA can lead to improvement of physical fitness, which is defined as either performance-related fitness or health-related fitness. Performance-related fitness is related to those components that are required for optimal work or sport performance and depends on individual cardiorespiratory capacity, muscular strength, motor skills, speed, power, and endurance, among other attributes. Conversely, health-related fitness is related to those components that positively or negatively affect PA and are associated with the individual’s overall health status. Health-related fitness is defined as the ability to perform daily activities with different traits and capacities that lower the risk of developing chronic diseases or premature death(7). Overall, LTPA performed with a sufficiently high intensity level can lead to cardiorespiratory and musculoskeletal fitness. Other health benefits include lower blood pressure and cholesterol levels and lower risk for type 2 diabetes, obesity, heart disease, stroke, cancer, and all-cause mortality(27-29).

Occupational physical activity (OPA) is performed while working. Activities under OPA include stocking shelves in a store, preparing or serving food in restaurant, delivering packages in an office, or carrying tools in a garage(6).

There was considerable interest in epidemiological research on high OPA in the past, as OPA in particular can be sustained for 30 to 40 h per week for several years. This is still true in some occupations, but in recent years heavy physical labor has accompanied occupations that include low levels of PA or even sedentary behavior(7). A majority of earlier studies agreed that OPA has some protective effect against cardiovascular disease(30). However, according to recent evidence, and in contrast to LTPA, the beneficial health effects in OPA may be not only insufficient to protect against cardiovascular disease but may also be detrimental to health(5,9). This could be explained by the fact that OPA includes longer periods of lower intensity levels of PA that do not maintain or improve cardiorespiratory fitness or cardiovascular health.

Therefore, OPA may elevate the 24-h heart rate and blood pressure and impair cardiovascular health(11,22). In a recent meta-analysis, Coenen et al. (12) found that men with high levels of OPA had an 18% increased risk of all-cause mortality as opposed to men with low levels of OPA. In addition, a prospective association between decreased OPA and increased BMI was not observed in a recent study, indicating that OPA is not effective in prevention of weight gain (31). Furthermore, the risk of impairments in physical health functioning may increase due to physical heavy lifting with constrained activities and postures(32,33). In addition, male blue-collar workers tend to participate more in OPA than their executives and white-collar workers, or women in

(19)

blue-collared occupations(12,30). However, even if recent studies suggest against the detrimental health effects of OPA, the review of Cillekens et al.(34) found not only favorable associations for most health-related outcomes with high OPA levels, but also unfavorable associations. Therefore, more high- quality research is warranted to quantify the levels of OPA and associated health effects.

Household physical activity (HPA) is performed in or around an individual’s home. HPA includes tasks such as cooking, home repair, yardwork, cleaning, or gardening(6). Since the development of automation, most HPA falls into the light category of PA. However, there are still chores that involve demanding physical tasks, such as manual yardwork or repairing, playing with children, or taking care of the elderly(7). A previous study revealed that retirement is associated with an increase in HPA, particularly among women(35). Furthermore, among older adults, HPA has previously been associated with health benefits and a lower level of deficit accumulation(36).

Overall, there are only a few existing studies on HPA and health effects. Besson et al. reported that an intense level of HPA (>5 METs) is associated with a reduction in all-cause mortality among older adults(37). However, HPA has been shown to have a greater contribution to total PA in females(38).

Moreover, even though leanness (in contrast to obesity) is associated with a reduced risk of mortality, there is insufficient evidence to support any associations between overweight or obesity and HPA(38,39).

Transportation physical activity (TPA) is performed when moving from one place to another. Examples of TPA include walking or bicycling to and from work, school, transportation hubs, or a shopping center(6). In Finland, each inhabitant made about one thousand domestic trips in 2016, averaging 2.7 daily trips per person, wherein 30% of all of trips were performed by walking or by bicycle(40). Overall, the convenience of motorized transportation has increased the sedentary time spent by an individual, while the dependence of physically-demanding transportation has decreased(41). According to previous evidence, TPA (specifically walking and cycling) is associated with health benefits such as reduced risk of type 2 diabetes and lower all-cause mortality(42). In addition, regular commuting (i.e., walking or bicycling) reduces the risk of ischemic stroke among Finnish adults aged 25 to 64 years (43). Moreover, the benefits of TPA exceed traffic-associated detriments associated with accidents or pollution (44).

Sedentary behavior includes any waking behavior with an energy expenditure of ≤1.5 METs while sitting, reclining, or lying. Driving a vehicle, sitting while watching television, and most office work are examples of sedentary behaviors(6). Public health reference values for sitting time have not emerged until very recently, probably because sedentary time has not been considered harmful to health. In addition, global progress to increase PA has been slow, mainly due to lack of awareness and investment(45). The dramatic decline in daily regular PA has increased a variety of health problems that are associated with a sedentary lifestyle(7). Physical inactivity is linked to reduced

(20)

metabolism, overweight and obesity, reduced glucose tolerance, high blood pressure, high cholesterol, and mental disorders such as depression(46).

Biswas et al. (2) observed that overall sedentary time or sitting time (either television or screen time) is associated with an increased incidence of cardiovascular disease, certain types of cancer, type 2 diabetes, and all-cause mortality in adults. However, increased moderate- or vigorous-intensity PA among older men and women appears to reduce the mortality risk associated with high sitting time, but not the risk associated with high TV-viewing time(47). In some countries, the amount of sedentary behavior can be as high as 70%, which is due to the increased use of technology and urbanization or changing patterns of transportation(45). The World Health Organization has recently recommended that adults aged 18 to 64 years should limit the amount of sedentary time and replace it with PA of any intensity to provide beneficial health benefits. Furthermore, adults should aim to exceed the recommended levels of moderate-to-vigorous intensity PA to help reduce the detrimental health effects of high levels of sedentary behavior(48).

Table 2 Domains of physical activity and examples. Modified from Strath et al.(49)

2.2. WORK ABILITY AND PHYSICAL OR MENTAL DEMANDS OF WORK

2.2.1 CONCEPT OF WORK ABILITY

Work is viewed in the context of activities of an individual’s achievements among different feelings, such as positive relationship, self-achievement, recognition, and purposeful activity. In addition, the centrality and the meaning of work have a positive influence on a worker’s life. It is significant in the totality of personal life and has potential interference with other domains of life, such as leisure, community, and family involvement(50). Work ability is considered as an important part of national government programs in multiple European Union countries. The general aim is to prevent sickness absence or premature retirement by improving the length of work careers and promoting coping at work, while better understanding the whole concept.

Hence, a better understanding offers better possibilities to promote work ability in general(51).

In Finland, the concept of work ability emerged in the 1980s and 1990s when a research group studied municipal employees in their midlife and

Domain Examples

Occupational Work related: manual labor tasks, walking, carrying or lifting objects Leisure time Engaged with free time: sports, hobbies, exercise

Transportation Purpose to go somewhere: bicycling, walking, standing while riding transportation Household Housework: chores, housework, yard work, childcare

Sitting Sitting while at work, at home, while studying, during free time

(21)

followed it with a longitudinal study(52-54). Work ability relates to a worker’s physical and mental capacities and the demands of the job or work environment, and can be used as a tool by professionals for disease and injury prevention and health promotion(15). However, assessing work ability can be challenging due to the complex, multidimensional, and diverse nature of the concept in addition to the constant change in the field of research and in work itself. Therefore, more estimations of the workforce at an individual level have become necessary to support existing results. Furthermore, the previously used subjective methods are reported to predict future work ability and disability at a good level(51). Consequently, lowered work ability can also be conceptualized as work disability. Similar to work ability, work disability holds multiple dimensions such as biomedical, psychosocial, biopsychosocial, ergonomic, or ecological aspects. These dimensions simultaneously interact with employment or well-being of a worker(55). In other words, analysis of work ability aims to demonstrate and reveal how work-related physical or psychological impairment prevents or constrains a person’s working capacity(55). For example, physical (biomedical) impairment relate to pain or musculoskeletal limitations, while psychological (psychosocial) relate to physiological functioning and determine how an individual handles stress(55,56).

2.2.2 MODELS OF WORK ABILITY

Work ability can be viewed as a multidimensional concept that encompasses several factors. There are various models that define and explain work ability.

One of the multidimensional work ability models was initiated by the Rehabilitation Foundation in Finland, wherein the model examines three individual factors that affect work ability. These factors are coping at work (e.g., physical and mental capacity, endurance), having control over one’s work (occupational skills and competence), or participation in the work community (general skills in work life and social skills)(51). Another model that is used to investigate work ability, the balance model by Rohmert and Rutenfranz, examines the degree of strain that occupational stress creates within the individual(57). Moreover, this dynamic model signifies the constant search for balance between an individual’s work life through work ability or the preservation of health that could associate with negative physiological or psychological work-related symptoms(51). Ilmarinen describes it as a building with several floors (Figure 3), wherein health and physical, mental, and social functioning comprise the first floor; the sounder the foundation, the stronger the work ability will be throughout the individual’s work life(51,58).

(22)

Figure 3 Dimensions and related factors of work ability (modified from Ilmarinen(58)).

Despite the previously mentioned more holistic and multidimensional models, the main focus has been for years on the individual’s physical ability or impairment under work ability. The shift of the focus to a more multidimensional way of conceptualizing began partly with the addition of mental health to the concept of work ability or disability(55). Considering this challenging concept and acknowledging its complicated nature, this study is focused on the physiological and psychological health factors between work ability, which can be seen as one of the core factors under several models.

2.2.3 PHYSICAL AND MENTAL DEMANDS OF WORK

Workers perform under a continual process of self-regulation while simultaneously performing job tasks and maintaining a balance between work activity and physical or mental well-being. Furthermore, the worker provides a perspective for understanding physical and organizational demands that include posture, work style, pacing, and tool use, among other considerations(59). Most job descriptions require some levels of PA that involve physical workload, for instance high physical effort, awkward postures, repetitive motions, or heavy loads(60). Moreover, there is a complicated interaction of the many factors that affect the relationship between work rate and work capacity that result in work performance (Figure 4)(46).

(23)

Figure 4 Factors that affect work performance (modified from Åstrand et al.(46).

Previous practical experience has indicated that a workload taxing 30-40% of the individual’s maximal oxygen uptake is considered a reasonable average upper limit for physical work over a regular 8-h working day(61). Additionally, no more than 40% of maximal muscle strength should be applied in repetitious muscular work(46). In the USA, the National Research Council and Institute of Medicine have developed a conceptual model of the possible roles and influences that may be associated in the development of musculoskeletal disorders among workers (Figure 5)(60). Moreover, this model illustrates the types of individual physical strains of the worker and how they relate to possible outcomes.

(24)

Figure 5 A model of the possible roles and influences wherein various factors associate with physical work demands and development of musculoskeletal disorders. Modified from National Research Council of Medicine(60).

Other jobs can include less physical exertion (sitting or standing for prolonged periods, monotonous tasks) with higher mental strain (customer work, deadline pressure)(59). The World Health Organization recognizes such work and its related conditions to have an impact on mental well-being and health(62). A research model by Nelson and Simmons presents five examples of stressors and their health consequences (Figure 6). These examples are role demands, interpersonal demands, physical demands, workplace policies, and work conditions(50). Consequently, all types of work demands can cause challenges to health conditions and are associated with prolonged work disability that simultaneously require workplaces to acknowledge these scenarios(59).

(25)

Figure 6 Holistic Model of Stress. Modified from Nelson & Simmons(63).

2.2.4 WORK ABSENTEEISM AND PRODUCTIVITY LOSS AT WORK (WORK PRESENTEEISM)

Chronic pain is common in Europe and elsewhere and burdens employers, individuals, the healthcare system and, society in general. In addition, chronic pain is more prevalent among manual workers and the unemployed and impairs an individual’s health status, HRQoL, work-related issues (i.e.

reduced work effectiveness), and functioning(64,65). It is also estimated that a large proportion of work absence is linked to psychological disorders(66).

While health-related costs are growing rapidly, mainly because of the aging of the working population, researchers have focused more on absenteeism (not attending work due to illness) and presenteeism (attending work while ill) and their consequences in public health and economy(66-68). Even though the impacts of absenteeism are currently well documented, more evidence is needed to explain the different causes of health-related unproductiveness(69).

Most sick workers stay at home while ill, but a growing number of workers will show up to work, despite their medical condition and regardless of impairment due to physical or psychological health problems. Hence the term presenteeism(66).

Results of research on the economic consequences of disease and illness have emerged recently. The results indicate that the disease of interest will lead to substantial costs due to sickness absence, disability, and productivity loss at work(59). Furthermore, the negative effects of presenteeism are associated with reduced physical(70,71) or mental health(70,72) and impaired work ability(70), although the measurement methods for presenteeism have been somewhat inconsistent(73,74). Finnish researchers observed that chronic pain is associated with early retirement due to disability, and 30% of male participants had medically certified absence that lasted more than 2

(26)

weeks(64,65,75). Furthermore, in Finland the cost of labor input lost due to sickness absence or presenteeism was approximately 3.4 billion Euros each in 2014(76). Therefore, it is important to find solutions to manage absenteeism without creating presenteeism(66). One solution to this could be promoting PA among employees, as previous studies have found inverse relationships between PA and absenteeism or presenteeism(77-79). However, the evidence for an association between PA and presenteeism is still limited(80).

Figure 7 Modified framework of absenteeism and presenteeism. Modified from Lohaus &

Habermann(73).

2.2.5 ASSOCIATION BETWEEN PHYSICAL OR MENTAL WORK DEMANDS AND HEALTH

A previous study from Chandola and Zhang reported that adverse working conditions are associated with poor health, while workers benefitted from proper working conditions and such conditions played a protective role for both physical and mental health(81). Several occupations involve high physical demands, wherein metabolic demands exceed the recommended limit within a work day while consuming one third of the worker’s maximal aerobic capacity, which may result in overload(82,83). In addition, Andersen et al. observed that high physical work demands increased the risk for long- term sickness absence, which underlines the importance of targeting possible risk factors and relevant prevention methods (84,85).

Moreover, previous studies have shown that poor work ability is associated with long-term sickness absence and work disability, an increased risk of early retirement, increased musculoskeletal pain, decreased functional ability, and greater mortality in old age(54,86-91). Furthermore, previous evidence has shown that more physically active occupations (e.g., construction) have a higher risk of work-related disability than less physically demanding occupations (92). In addition, a previous study revealed that a little less than

(27)

a third of male employees in Finland consider their work as physically demanding(16). Moreover, work itself is insufficient to prevent decline in work ability; measures to promote work ability should start before middle age, especially among workers in physically demanding jobs (52).

However, in several white-collar employees, less daily OPA is associated with negative experiences, such as work-related fatigue and burnout with prolonged work-related stress due to time pressure, excessive workload, or organizational change(93-95). Burnout is a severe form of fatigue that occurs after a long period of work stress and reduces work ability. The annual costs due to burnout has risen in Europe to 200 billion euros(96).

2.2.6 THE CONTRADICTION BETWEEN PHYSICAL ACTIVITY AND HEALTH AT WORK OR LEISURE

According to Lear et al., OPA is the most time consuming form of PA for most people between all subdomains, which is even more evident in lower-income countries where LTPA is negligible (26). The movements during LTPA are characterized as dynamic movements that are performed voluntarily over a short period of time, which provide the individual sufficient time for recovery(97). Conversely, OPA often includes more static work of longer duration with a purpose, design, and social context considerably different from that of LTPA(97). The demands of the working environment consist of the production of individual workers that form a larger part of the workforce.

Productivity is of paramount importance and the environment and social organization of work are designed to maximize efficiency or profit, without necessarily acknowledging the health of the workers(5). Furthermore, OPA can restrict the daily activity of a worker, depending on the job description of the individual. For instance, an office worker may be restricted predominantly to sitting, a manufacturing worker in a production line to standing, a cleaner to walking, or a construction worker to heavy lifting(5). These types of labor usually contain monotonous and repetitive movements with awkward postures that require workers to exert themselves throughout most of their workday without sufficient recovery time(5). Therefore, this type of PA during work increases the risk of cardiovascular disease by increasing daily heart rate, blood pressure, and inflammatory markers, which are detrimental to cardiovascular health(5).

Most of the recent studies on OPA and adverse health effects describe the negative consequences on cardiovascular health and mortality based on cardiovascular disease (CVD) outcomes(12,98,99). There is also evidence that suggests that OPA increases several musculoskeletal conditions, such as lower back pain due to heavy lifting(100), prolonged standing, or other types of physical occupational demands(101,102), or neck and upper limb pain from awkward manual occupational positions (103). In contrast, LTPA protects against coronary heart disease(104) and mortality(105), lower back pain(106), and upper limb and neck pain(107). This contradiction, or paradox, between LTPA and OPA is presented in Table 3.

(28)

Table 3 Different characteristics of OPA and LTPA and how they affect physiological factors and health outcomes. Modified from Holtermann et al.(5)

PA-CHARACTERISTICS OPA LTPA

Types of activities Prolonged postures and manual handling

Dynamic movements with large muscle

groups Duration Long periods (several

hours or even a full shift, for many consecutive days,

weeks, and even years)

Short periods (<1 h)

Recovery Low High

Intensity Relatively low (<60%

of the maximum aerobic capacity)

Relatively high (>60% of the maximum aerobic

capacity Physiological

responses

Chronic increase in ventilation, heart rate,

blood pressure, metabolism, and inflammation markers

Instantaneous short increase in ventilation, heart rate, blood pressure,

metabolism, and inflammation markers Increased 24-h blood

pressure and heart rate

Decreased 24-h blood pressure and

heart rate Mechanical stress

and injury of the arterial wall (atherosclerosis)

Fitness improvements

Health

outcomes Cardiovascular health

deterioration Cardiovascular health improvement Higher risk of

mortality

Lower risk of mortality

2.2.7 EVIDENCE ON THE ASSOCIATION BETWEEN LEISURE- TIME PHYSICAL ACTIVITY AND WORK DEMANDS

A prospective study by Clays et al. revealed an overall beneficial effect of LTPA and an unfavorable relationship of physical work demands with CV health among 14 337 middle-aged men free from coronary heart disease at baseline(108). Moreover, Holtermann et al. tested the hypothesis that OPA and LTPA provide similar benefits. However, the results rejected this hypothesis, as LTPA decreased the risk of long-term sickness absence and OPA increased such risk(109). Fimland et al. reported similar results wherein high OPA was associated with disability pensions and musculoskeletal disorders;

the converse was observed with LTPA regardless of work type(13). In addition, high-intensity LTPA decreased work-related fatigue in workers with physically demanding jobs. Moreover, older workers seemed to participate less in LTPA than younger workers.(110). However, a systematic review by Kirk and Rhodes concluded that the lack of OPA, or the sedentariness of the job, increased the risk of inactivity in these workers during leisure time(111). Sedentary

(29)

workplace behavior together with lack of LTPA is associated with musculoskeletal pain, work-related fatigue, and a higher risk for heart failure or burnout(95,96).

In summary, previous evidence emphasizes the importance of the amount of LTPA or lack thereof, and its beneficial or detrimental association with OPA on several health risks.

2.2.8 EVIDENCE ON THE ASSOCIATION BETWEEN LEISURE-TIME PHYSICAL ACTIVITY AND WORK ABILITY

There is currently strong scientific evidence on the deleterious health effects of a sedentary lifestyle and the beneficial effects of PA among healthy adult populations(2,27). However, there is a need for further research on the specific dimensions of PA and work ability. A previous review presented associations between the lack of vigorous LTPA and lower work ability(14). In addition, cross-sectional studies revealed better work ability among sedentary workers and among middle-aged workers with physically demanding jobs with higher levels of LTPA(112,113). Moreover, a cross-sectional and prospective study by Arvidson et al. revealed that an increased amount of LTPA decreased the likelihood of poor or moderate work ability as reported by Swedish health care workers who were mostly women(114). Another prospective study from Finland revealed that LTPA is inversely associated with job strain, job demands, and job control among participants aged 24 to 39 years(115).

Furthermore, a cross-sectional study by Norheim et al. revealed that high- intensity LTPA is associated with greater work ability among manual workers aged 50 to 70 years(116). A cross-sectional study from Norway revealed associations between lower work ability and several lifestyle risk factors, such as lower levels of PA, obesity, smoking, and unhealthy diet(117). In addition, Hult et al. observed that high-intensity PA is associated with greater work ability among unemployed Finnish men and women(118).

More randomized controlled trials (RCT) are warranted. Kettunen et al.

revealed that a 12-month physical exercise intervention improved cardiorespiratory fitness in healthy workers and was associated with better work ability(119). Other studies have investigated on-site exercise intervention and work ability and have yielded inconsistent results. In an RCT study among construction workers, there were no significant changes in work ability, pain, productivity, perceived physical exertion, or sick leave in the 12-week intervention group, which included exercise training 3 x 20 minutes per week.

However, an increase of 10% in VO2max was found(120). Conversely, physical exercise was an effective method in preventing deterioration of work ability among female health care workers(121).

(30)

2.3 HEALTH-RELATED QUALITY-OF-LIFE (HRQoL)

2.3.1 GENERAL CONCEPT OF HRQoL

Quality-of-life is one of the major concerns in a modern society, and it is assumed that we have a higher quality-of-life than our predecessors.

Furthermore, quality-of-life is an important domain of health and illness, wherein the application of the concept is known as health-related quality-of- life (HRQoL)(122). HRQoL is a multi-dimensional concept that includes mental, physical, and social components of functioning(123). Moreover, HRQoL can be defined by the way that a person functions in their life and their perceived wellbeing in the mental, physical, and social domains of health(124).

The concept of HRQoL has evolved since the 1980s to comprise aspects of overall quality-of-life that affect physical or mental health(125,126).

Consequently, the importance of HRQoL has been recognized in recent years and the focus has shifted from only medical cure of disease to the inclusion of HRQoL assessment along with clinical parameters(122). Different chronic diseases, such as depression, back pain, knee osteoarthritis, type 2 diabetes, and cancer are known to impair the physical and mental aspects of HRQoL(127-129). Furthermore, measuring HRQoL can help determine the burden of preventable injuries, diseases, and disabilities and provide new insights into the relationships between HRQoL and different risk factors(130).

2.3.2 EVIDENCE ON THE ASSOCIATION BETWEEN PHYSICAL ACTIVITY AND HRQoL

Previous studies and systematic reviews have found associations between PA and HRQoL among the general population of children and adolescents(131), healthy adult men and women(132,133), and elderly populations(134,135).

Furthermore, several studies have found positive associations between LTPA and physical (136-139) or mental (136,138,140) component scores of HRQoL.

In addition, low levels of PA with high screen time are negatively associate with HRQoL(141). Overall, the evidence is strong that greater amounts of PA are associated with a positive perception of quality-of-life among the general population(4). However, the data are limited on the relationship between domain-specific PA and HRQoL. An increased understanding of how the different PA domains associate with HRQoL can help create strategies to prevent the deleterious health effects of sedentary lifestyles.

2.4 DEPRESSIVE SYMPTOMS

2.4.1 ROLE OF DEPRESSION AMONG THE SOCIETY

The WHO estimates that approximately 320 million individuals are living with depression (142). Furthermore, over a third of the total EU population is living with mental disorders. Depression has become a challenge for health care in

(31)

both disease diagnosis and creating preventive strategies(143). Depressive disorders are considered as the single greatest contributor to nonfatal health loss globally. In addition, mental disorders in general are major contributors to the global burden of diseases(144). Most people with depressive disorders do not receive treatment(145). Symptoms of depression are diverse and include low mood or loss of interest, sleep disturbances, and feelings of inadequacy and hopelessness (146).

2.4.2 EVIDENCE ON THE ASSOCIATION BETWEEN PHYSICAL ACTIVITY AND DEPRESSION

PA has strong evidence for health benefits, including reduced risk of stroke, CVD, obesity, cancer, and reduced overall mortality. In addition, PA also improves musculoskeletal health and stress regulation. Nevertheless, the positive associations of PA on depression and mental health are still inconsistent(147,148). There is supporting evidence on PA and psychological benefits for individuals with mild to severe emotional illnesses and on how specific exercise variables positively affect psychological outcomes. However, there is also evidence that suggests that exercise is not necessarily associated with beneficial psychological outcomes, and could even result in detrimental changes to emotional health(7). According to previous systematic reviews, exercise may be an effective method to treat or prevent symptoms of depression(149-152). However, more studies are needed to identify individual antidepressant moderators of the psychological, biological, and clinical effects of exercise (152). Moreover, some different life domains diminish the relationship between PA and mental illness, whereas promoting LTPA may be most beneficial for mental health promotion and prevention (153). Although previous evidence has indicated several psychosocial mechanisms of the effect of PA on mental health, there is still little evidence as to whether these mechanisms play the same role in different PA domains(153). Moreover, depressive disorders are associated with decreased HRQoL(154).

Furthermore, work-related factors are known to represent risk factors for depression, and work ability is considered an important aspect of well-being and health status(155). In addition, increased PA can improve work ability or the health status of an individual(14,27).

(32)

3 THE AIMS OF THE STUDY

This study examined the relationships between PA and different indicators, such as HRQoL and work ability. The main focus was to examine how the sub- domains of PA, LTPA in particular, relate to mental and physical functioning or work ability in different work requirements between adult men aged 20 to 40 years. In addition, the determinants of mental health, such as depression symptoms, were assessed for associations between LTPA and work ability.

The specific aims of the present study were to examine:

1. the relationships between domains of PA, sedentary lifestyle, and HRQoL (Study I)

2. the relationships between LTPA and work ability and different occupational physical demands (Study II)

3. the relationships between LTPA and ability to meet different work requirements among workers with or without current or present depressive symptoms (Study III)

4. whether the domains of PA relate differently to work ability, and whether these relationships vary with perceived physical or mental demands of work (Study IV)

(33)

4 METHODS

4.1 STUDY DESIGN AND DATA COLLECTION

At baseline, 5000 male participants (born in 1969, 1974, 1979, 1984, or 1989) were randomly selected in 2009 from the population register as a population sample from those who had performed, discontinued the military service or had performed an alternative non-military service. Immigrants, imprisoned persons, or persons with diagnosed mental disorders were excluded from the study (Figure 8).

Figure 8 Flowchart of study participants, data collection, and response rate. YOB=year of birth.

4.2 PARTICIPANTS

After the random selection of 5000 men between the five age cohorts, a questionnaire that included several instruments was sent via mail to the selected group. The response rate for the questionnaires was 28.5%. The data were collected for a detailed analysis in 2010.

(34)

4.3 VARIABLES

Physical activity

The long version of the International Physical Activity Questionnaire (IPAQ) is one of the commonly used tools to measure PA in large samples. The IPAQ was developed for adults aged 18 to 65 years to assess population levels of PA across countries(156). In this study, IPAQ was used to collect information about participants’ PA and daily sitting time. The IPAQ assesses detailed PA levels in four different domains (occupational [OPA], leisure time [LTPA], household [HPA], and transportation [TPA]). To provide domain-specific scores, the domains OPA, LTPA, and HPA contain three levels of intensity (walking, moderate, or vigorous), whereas TPA includes only two levels (moderate and vigorous) of intensity. In addition, IPAQ assesses and provides information about the time a person spends sitting while at work, while doing course work, during leisure time, or at home. Questions require respondents to recall their PA during the past 7 days. Each type of activity is weighted by its energy requirements defined in MET minutes per week. To obtain a MET score in hours/week (MET-h/week), the MET value is multiplied depending on the intensity (3.3 for walking, 4.0-6.0 for moderate-intensity activity, and 8.0 for vigorous-intensity activity) and is converted to hours with duration (minutes) and frequency (days). The long form of IPAQ is a valid and reliable instrument to assess the levels and patterns of PA(157). Furthermore, it can be culturally adapted to the Finnish population(158).

However, sitting time is not included as a part of PA and the time the respondent has spent sitting during travel under the transport domain is also excluded. Unlike MET-minutes, where intensity is considered, minutes are used to indicate the time spent sitting. This indicates the average time a respondent spends sitting per day. The following formula is used to calculate the sitting time, wherein weekday (a) sitting minutes are multiplied by 5 weekdays and weekend (b) day sitting minutes are multiplied by 2 weekend days(159):

ܵ݅ݐݐ݅݊݃ ݐ݅݉݁=(ܽ× 5 +ܾ× 2) 7 Health-related qualify of life

The 36-item Short Form Survey (SF-36) was used to assess HRQoL. The SF- 36 survey consists of eight different domains that measure physical functioning wherein each category is scored on a scale of 0-100; 0 indicates for the worst overall health status whereas 100 represents the best health status(160). The scales included in the SF-36 indicate separate but conceptually related aspects of HRQoL; the overall level of subjectively estimated HRQoL is indicated by the scale’s score profile. The scales of physical role functioning, and physical functioning reflect the respondent’s self-rated ability in mobility and activities in daily living. In addition, the other scales cover energy and vitality, emotional well-being, general health, bodily

(35)

pain, and limitations in role functions and interaction (emotional role functioning, social functioning)(161). In our study, the following four scales contributed to the scoring of the Physical Component Summary (PCS):

Physical Functioning, Role-Physical, General Health, and Bodily Pain.

Furthermore, the following four other scales contributed to the Mental Component Summary (MCS): Mental Health, Vitality, Role-Emotional, and Social Functioning.

Work Ability

The Work Ability Index (WAI) was used to measure work ability. The WAI is a self-reported instrument that assesses work ability, symptoms and diagnoses, and sickness absence to measure the functional capacity and health through a single dimension of work ability(162). Overall, the WAI consists of seven items that include both physical and psychological aspects of work ability. Scores of the WAI range from 7 (lowest) to 49 (highest) and form the basis for determining the level of work ability based on to the following scales: 7-27 (“poor” work ability), 28-36 (“moderate” work ability), 37-43 (“good” work ability), and 44-49 (“excellent” work ability) (162,163). The WAI is a valid instrument for assessing work ability(164).

Table 4 Grading the level of work ability and the necessary measures according to the Work Ability Index. Modified from Rautio and Michelsen(163).

Score Work ability Measures

7-27 Poor Recovery of work ability

28-36 Average Promotion of work ability

37-43 Good Strengthening of work ability

44-49 Excellent Maintenance of work ability

Depressive symptoms

The Beck Depression Inventory (BDI)(165) was used to assess the occurrence of depressive symptoms. In this study, items 1 and 4 with a cut-off of ≥1 were used to estimate symptoms. Item 1 consists of the following responses (scoring in brackets): “I do not feel sad (0), I feel sad (1), I am sad all the time and I can’t snap out of it (2), I am so sad and unhappy that I can’t stand it (3)”. Item 4 consists of the following responses: “I get as much satisfaction out of things as I used to (0), I don’t enjoy things the way I used to (1), I don’t get real satisfaction out of anything anymore (2), I am dissatisfied or bored with everything (3)”. Items 1 and 4 measure the essential diagnostic criteria of depression, such as depressive mood and loss of pleasure(166).

4.4 STATISTICAL METHODS

The data in studies I-IV are presented as means with standard deviations (SD) for continuous variables, median and interquartile range (IQR) for ordinal/continuous variables, and as frequencies with percentages for