Downloaded from http://oem.bmj.com/ on March 15, 2015 - Published by group.bmj.com
Workplace
ORIGINAL ARTICLE
Association of physical workload and leisure time physical activity with incident mobility limitations: a follow-up study M Mänty,1,2,3 A Møller,4,5,6 C Nilsson,1 R Lund,1 U Christensen,1 K Avlund1,2,7 For numbered affiliations see end of article. Correspondence to Dr Minna Mänty, Department of Public Health, Hjelt Institute, University of Helsinki, P.O. Box 41, Helsinki FIN-00014, Finland; minna.manty@helsinki.fi Received 25 September 2013 Revised 9 May 2014 Accepted 15 May 2014 Published Online First 30 May 2014
ABSTRACT Objectives To examine individual as well as joint associations of physical workload and leisure time physical activity with incident mobility limitations in initially well-functioning middle-aged workers. Methods This study is based on 6-year follow-up data of the Danish Longitudinal Study on Work, Unemployment and Health. Physical workload was reported at baseline and categorised as light, moderate or heavy. Baseline leisure time physical activity level was categorised as sedentary or active following the current recommendations on physical activity. Incidence of mobility limitations in climbing stairs and running among initially well-functioning workers (n=3202 and n=2821, respectively) was assessed during follow-up. Results Higher workload increased whereas active leisure time decreased the risk of developing mobility limitations. The incidence of limitations increased progressively with higher workload regardless of level of leisure time physical activity, although the risks tended to be higher among those with sedentary leisure time compared with their active counterparts. All in all, the risk for onset of mobility limitations was highest among those with heavy workload combined with sedentary leisure time and lowest among those with light workload combined with active leisure time. Conclusions Although leisure time physical activity prevents development of mobility decline, high workload seems to accelerate the progression of mobility limitations among both those with active and sedentary leisure time. Therefore, efforts should be made to recommend people to engage in physical activity regardless of their physical workload.
INTRODUCTION
To cite: Mänty M, Møller A, Nilsson C, et al. Occup Environ Med 2014;71:543–548.
Adequate physical functioning is required for managing daily life independently, and limitations in mobility, such as difficulty in walking, have been shown to predict various poor health outcomes and mortality later in life.1–4 Hence, restrictions in physical functioning are considered as important outcomes in epidemiological and intervention studies.5 Many cross-sectional as well as retrospective studies have indicated that physical workload is inversely related to physical functioning among middle-aged and aging workers.6–10 Although, mixed or even opposite results especially among younger workers have also been observed.11–14 To date, some prospective longitudinal studies have been reported in the area15–19 and all these have
Mänty M, et al. Occup Environ Med 2014;71:543–548. doi:10.1136/oemed-2013-101883
What this paper adds ▸ Previous studies have indicated that high physical workload accelerates, while leisure time physical activity postpones functional decline. ▸ The effects of physical workload on functional decline have been mainly studied in small samples of specific working populations, and it is not known whether leisure time physical activity could prevent the deteriorating effects of high physical workload on physical functioning. ▸ The results of this longitudinal study among Danish workers suggest that the risk of developing functional limitations increases progressively with higher workload regardless of the level of leisure time physical activity, although the risk tends to be higher among those with sedentary leisure time compared with their active counterparts. ▸ Engagement in leisure time physical activity should be encouraged regardless of the level of physical workload, and optimal interventions to prevent functional decline among those with physically demanding work should be elucidated.
indicated a negative effect of high physical workload on physical functioning. However, most of these studies have included relatively small study samples and/or included only specific working populations, such as workers with inflammatory joint conditions or industrial employees. Therefore, population-based longitudinal studies are warranted in the area. In contrast to the physical workload, many observational and intervention studies have suggested beneficial effects of leisure time physical activity on physical functioning in middle-aged and ageing populations.20–24 However, it is not known whether leisure time physical activity could prevent the deteriorating effects of high physical workload on physical functioning. Using the Danish Longitudinal Study on Work, Unemployment and Health, we first examine individual associations of physical workload and leisure time physical activity with risk of developing mobility limitations in middle-aged workers during a 6-year prospective follow-up. Second, we describe 543
Downloaded from http://oem.bmj.com/ on March 15, 2015 - Published by group.bmj.com
Workplace the joint associations of physical workload and leisure time physical activity with onset of mobility limitations.
METHODS Design and study population The present study is based on data from the Danish Longitudinal Study on Work, Unemployment and Health. The study has been described in detail elsewhere25 and is approved by The Committees on Biomedical Research Ethics of the Capital Region of Denmark. The study population included a random sample of Danish adults aged 40 and 50 years in 1999 (n=11 082), comprising 10% of the Danish population aged 15 years or older. Baseline data were collected in 2000 by postal questionnaire (n=7588, response rate 69%). Follow-up data were collected by a postal questionnaire in 2006 on surviving participants and participants who had not emigrated or refused to participate in scientific studies (N=4893, response rate 71%). Non-responders of the 2006 questionnaire differed somewhat from responders. More men than women and more persons with low socioeconomic status did not respond to the questionnaires. There were no significant differences between responders and non-responders regarding number of contacts with general practitioner. In this paper, individuals who were part of the workforce at baseline, with full records on all study variables, and without any mobility limitations at baseline constituted the study population (n=3202 for climbing stairs, n=2821 for running). Among the working population with full records on all study variables, 89% and 78% were without any mobility limitations in climbing stairs and running, respectively. The corresponding numbers for unselected baseline population were 82% and 72%. The selected participants tended to have slightly better health compared with excluded participants (data not shown).
Measures Mobility limitations in 2000 and 2006 were measured by a modified version of the Rosow–Breslau functional status measure,26 assessing whether the study participant feel limited, because of health problems, when running 100 m and climbing two flights of stairs, respectively, with the following response categories: ‘yes, very limited’, ‘yes, somewhat limited’ and ‘no, not limited at all’. Participants who reported being somewhat or very limited were considered as having limitations in that specific task. All results are presented separately for running and climbing stairs. Similar measures of mobility limitations have been shown to be useful measures in describing functional changes with increasing age27 and correlated with physical work demands among middle-aged individuals.9 28 Physical workload was measured at baseline by a question: “How would you describe the physical activity in your daily work?” with the following response alternatives: “heavy or fast work with physical strain”, “standing or walking work including occasional lifting or carrying burdens”, “standing or walking work without physical strain” and “mostly sedentary work without physical strain”. Physical workload was categorised as light (sedentary work), moderate (standing work with or without lifting) and heavy (heavy and demanding work). This question has been successfully used in several Danish studies on work exposures in working life.29 In addition, previous studies have indicated good reproducibility and validity for questions regarding general body postures and level of physical effort at work.30 Leisure time physical activity at baseline was evaluated by the following three questions: (1) “How many hours a week are you 544
physically active? Please include sport, physical training, gardening, walking and bicycle trips including transportation between work and home”; (2) “How many hours a week do you usually exercise so much that you get out of breath or sweat?” and (3) “How many hours a week do you participate in physical training or sport which strengthen your muscles, for example, gymnastics, body-building etc?” Response alternatives for the questions 1 and 2 were ‘none’, ‘half an hour’, ‘1 h’, ‘2–3 h’, ‘4–6 h’ and ‘7 h or more’, and the alternatives for the question 3: ‘none’, ‘less than 1 h’, ‘1–2 h’, ‘3–4 h’ and ‘5 h or more’. Participants were considered to be active it they reported leisure time physical activities at least 2–3 h per week (question 1) or vigorous intensity physical activities about an hour per week (question 2) and, in addition, reported muscle strength training at least 1–2 h per week (question 3). Participants who did not reach this level of activity were categorised as sedentary. This categorisation is comparable to current WHO Global Recommendations on Physical activity for Health.31 According to these recommendations, adults aged 18–64 should do at least 150 min of moderate-intensity aerobic physical activity throughout the week or do at least 75 min of vigorous-intensity aerobic physical activity throughout the week or an equivalent combination of moderate-intensity and vigorous-intensity activity. In addition, muscle-strengthening activities should be done two or more days a week.31 Covariates: The following covariates were measured at baseline and used in the multivariate analyses: gender, age, education, body mass index (BMI), smoking and chronic diseases. BMI was calculated on the basis of responses to questions regarding height and weight (weight (kg)/height (m)2) and divided into four groups: (1)
Workplace
ORIGINAL ARTICLE
Association of physical workload and leisure time physical activity with incident mobility limitations: a follow-up study M Mänty,1,2,3 A Møller,4,5,6 C Nilsson,1 R Lund,1 U Christensen,1 K Avlund1,2,7 For numbered affiliations see end of article. Correspondence to Dr Minna Mänty, Department of Public Health, Hjelt Institute, University of Helsinki, P.O. Box 41, Helsinki FIN-00014, Finland; minna.manty@helsinki.fi Received 25 September 2013 Revised 9 May 2014 Accepted 15 May 2014 Published Online First 30 May 2014
ABSTRACT Objectives To examine individual as well as joint associations of physical workload and leisure time physical activity with incident mobility limitations in initially well-functioning middle-aged workers. Methods This study is based on 6-year follow-up data of the Danish Longitudinal Study on Work, Unemployment and Health. Physical workload was reported at baseline and categorised as light, moderate or heavy. Baseline leisure time physical activity level was categorised as sedentary or active following the current recommendations on physical activity. Incidence of mobility limitations in climbing stairs and running among initially well-functioning workers (n=3202 and n=2821, respectively) was assessed during follow-up. Results Higher workload increased whereas active leisure time decreased the risk of developing mobility limitations. The incidence of limitations increased progressively with higher workload regardless of level of leisure time physical activity, although the risks tended to be higher among those with sedentary leisure time compared with their active counterparts. All in all, the risk for onset of mobility limitations was highest among those with heavy workload combined with sedentary leisure time and lowest among those with light workload combined with active leisure time. Conclusions Although leisure time physical activity prevents development of mobility decline, high workload seems to accelerate the progression of mobility limitations among both those with active and sedentary leisure time. Therefore, efforts should be made to recommend people to engage in physical activity regardless of their physical workload.
INTRODUCTION
To cite: Mänty M, Møller A, Nilsson C, et al. Occup Environ Med 2014;71:543–548.
Adequate physical functioning is required for managing daily life independently, and limitations in mobility, such as difficulty in walking, have been shown to predict various poor health outcomes and mortality later in life.1–4 Hence, restrictions in physical functioning are considered as important outcomes in epidemiological and intervention studies.5 Many cross-sectional as well as retrospective studies have indicated that physical workload is inversely related to physical functioning among middle-aged and aging workers.6–10 Although, mixed or even opposite results especially among younger workers have also been observed.11–14 To date, some prospective longitudinal studies have been reported in the area15–19 and all these have
Mänty M, et al. Occup Environ Med 2014;71:543–548. doi:10.1136/oemed-2013-101883
What this paper adds ▸ Previous studies have indicated that high physical workload accelerates, while leisure time physical activity postpones functional decline. ▸ The effects of physical workload on functional decline have been mainly studied in small samples of specific working populations, and it is not known whether leisure time physical activity could prevent the deteriorating effects of high physical workload on physical functioning. ▸ The results of this longitudinal study among Danish workers suggest that the risk of developing functional limitations increases progressively with higher workload regardless of the level of leisure time physical activity, although the risk tends to be higher among those with sedentary leisure time compared with their active counterparts. ▸ Engagement in leisure time physical activity should be encouraged regardless of the level of physical workload, and optimal interventions to prevent functional decline among those with physically demanding work should be elucidated.
indicated a negative effect of high physical workload on physical functioning. However, most of these studies have included relatively small study samples and/or included only specific working populations, such as workers with inflammatory joint conditions or industrial employees. Therefore, population-based longitudinal studies are warranted in the area. In contrast to the physical workload, many observational and intervention studies have suggested beneficial effects of leisure time physical activity on physical functioning in middle-aged and ageing populations.20–24 However, it is not known whether leisure time physical activity could prevent the deteriorating effects of high physical workload on physical functioning. Using the Danish Longitudinal Study on Work, Unemployment and Health, we first examine individual associations of physical workload and leisure time physical activity with risk of developing mobility limitations in middle-aged workers during a 6-year prospective follow-up. Second, we describe 543
Downloaded from http://oem.bmj.com/ on March 15, 2015 - Published by group.bmj.com
Workplace the joint associations of physical workload and leisure time physical activity with onset of mobility limitations.
METHODS Design and study population The present study is based on data from the Danish Longitudinal Study on Work, Unemployment and Health. The study has been described in detail elsewhere25 and is approved by The Committees on Biomedical Research Ethics of the Capital Region of Denmark. The study population included a random sample of Danish adults aged 40 and 50 years in 1999 (n=11 082), comprising 10% of the Danish population aged 15 years or older. Baseline data were collected in 2000 by postal questionnaire (n=7588, response rate 69%). Follow-up data were collected by a postal questionnaire in 2006 on surviving participants and participants who had not emigrated or refused to participate in scientific studies (N=4893, response rate 71%). Non-responders of the 2006 questionnaire differed somewhat from responders. More men than women and more persons with low socioeconomic status did not respond to the questionnaires. There were no significant differences between responders and non-responders regarding number of contacts with general practitioner. In this paper, individuals who were part of the workforce at baseline, with full records on all study variables, and without any mobility limitations at baseline constituted the study population (n=3202 for climbing stairs, n=2821 for running). Among the working population with full records on all study variables, 89% and 78% were without any mobility limitations in climbing stairs and running, respectively. The corresponding numbers for unselected baseline population were 82% and 72%. The selected participants tended to have slightly better health compared with excluded participants (data not shown).
Measures Mobility limitations in 2000 and 2006 were measured by a modified version of the Rosow–Breslau functional status measure,26 assessing whether the study participant feel limited, because of health problems, when running 100 m and climbing two flights of stairs, respectively, with the following response categories: ‘yes, very limited’, ‘yes, somewhat limited’ and ‘no, not limited at all’. Participants who reported being somewhat or very limited were considered as having limitations in that specific task. All results are presented separately for running and climbing stairs. Similar measures of mobility limitations have been shown to be useful measures in describing functional changes with increasing age27 and correlated with physical work demands among middle-aged individuals.9 28 Physical workload was measured at baseline by a question: “How would you describe the physical activity in your daily work?” with the following response alternatives: “heavy or fast work with physical strain”, “standing or walking work including occasional lifting or carrying burdens”, “standing or walking work without physical strain” and “mostly sedentary work without physical strain”. Physical workload was categorised as light (sedentary work), moderate (standing work with or without lifting) and heavy (heavy and demanding work). This question has been successfully used in several Danish studies on work exposures in working life.29 In addition, previous studies have indicated good reproducibility and validity for questions regarding general body postures and level of physical effort at work.30 Leisure time physical activity at baseline was evaluated by the following three questions: (1) “How many hours a week are you 544
physically active? Please include sport, physical training, gardening, walking and bicycle trips including transportation between work and home”; (2) “How many hours a week do you usually exercise so much that you get out of breath or sweat?” and (3) “How many hours a week do you participate in physical training or sport which strengthen your muscles, for example, gymnastics, body-building etc?” Response alternatives for the questions 1 and 2 were ‘none’, ‘half an hour’, ‘1 h’, ‘2–3 h’, ‘4–6 h’ and ‘7 h or more’, and the alternatives for the question 3: ‘none’, ‘less than 1 h’, ‘1–2 h’, ‘3–4 h’ and ‘5 h or more’. Participants were considered to be active it they reported leisure time physical activities at least 2–3 h per week (question 1) or vigorous intensity physical activities about an hour per week (question 2) and, in addition, reported muscle strength training at least 1–2 h per week (question 3). Participants who did not reach this level of activity were categorised as sedentary. This categorisation is comparable to current WHO Global Recommendations on Physical activity for Health.31 According to these recommendations, adults aged 18–64 should do at least 150 min of moderate-intensity aerobic physical activity throughout the week or do at least 75 min of vigorous-intensity aerobic physical activity throughout the week or an equivalent combination of moderate-intensity and vigorous-intensity activity. In addition, muscle-strengthening activities should be done two or more days a week.31 Covariates: The following covariates were measured at baseline and used in the multivariate analyses: gender, age, education, body mass index (BMI), smoking and chronic diseases. BMI was calculated on the basis of responses to questions regarding height and weight (weight (kg)/height (m)2) and divided into four groups: (1)
