- Email: [email protected]
The challenge of assessing physical activity in populations
or requires “high efficacy” by the receivers. In other words, we strongly believe that stressing the harms of inactivity could not only work but potentially be much more effective than stressing the benefits of activity, similar to the example of smoking.1 As we advocated in our Comment,1 it takes a comprehensive plan, with repeated and intensified delivery of key messages, to achieve success in the promotion of exercise. This is why we suggest implementation of an approach similar to MPOWER, such that multiple facets of behaviour that lead to inactivity can be combated simultaneously.4 Among lessons that we have learned from tobacco control, it is clear that national campaigns should not rely on a single action, but multipronged, comprehensive programmes. The more we learn from success stories in tobacco control, the more we believe in our proposal to stress the harms of inactivity. With 60–80% of people characterised as inactive,5 no one will feel threatened when told that lack of regular exercise is bad for them. In fact, the more we emphasise, the clearer the message. We declare that we have no conflicts of interest.
*Chi Pang Wen, Min Kuang Tsai, Xifeng Wu [email protected] Institute of Population Health Sciences, National Health Research Institutes, Zhunan, Miaoli County 350, Taiwan (CPW, MKT); China Medical University Hospital, Taichung, Taiwan (CPW, MKT); and Department of Epidemiology, MD Anderson Cancer Center, Houston, TX, USA (XW) 1
2
3
4
5
Wen CP, Wu X. Stressing harms of physical inactivity to promote exercise. Lancet 2012; 380: 192–93. World Lung Foundation and American Cancer Society. The tobacco atlas: harm from smoking. http://www.tobaccoatlas.org/harm/harm_ from_smoking/text/ (accessed Sept 18, 2012). WHO. WHO FCTC health warnings database. http://www.who.int/tobacco/ healthwarningsdatabase/en/index.html (accessed Sept 17, 2012). WHO, Research for International Tobacco Control. WHO report on the global tobacco epidemic, 2008: the MPOWER package. Geneva: World Health Organization, 2008. Wen CP, Wai JP, Tsai MK, et al. Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. Lancet 2011; 378: 1244–53.
www.thelancet.com Vol 380 November 3, 2012
The challenge of assessing physical activity in populations In your Series on physical activity (July 21) I believe that the challenge of measuring physical activity should have been given more attention. Most of the data presented in the Series are based on estimates of time spent in intensity levels. Nevertheless, no gold standard exists for the measurement of time spent in intensity levels in a reallife environment in a representative sample of the population and in a way that does not interfere with the behaviour of the study participants. As a consequence, the accuracy of both questionnaires and accelerometry to estimate time spent in intensity levels during daily life cannot be assessed. In other words, these physical activity data come with a measurement error that cannot be quantified. A similar problem applies to counting steps per day with pedometers. The problem described above complicates both innovation of measurement techniques and interpretation of the collected data. Reconsideration of what it is that we want to measure might be necessary. Paradoxically, however, methodological innovation is impossible without violation of methodological consistency, yet both are needed for reliable physical activity research. I declare that I have no conflicts of interest.
Vincent van Hees [email protected] Movelab, Institute of Cellular Medicine, Newcastle University, Newcastle-upon-Tyne NE2 4HH, UK; and MRC Epidemiology Unit, Institute of Metabolic Science, Cambridge, UK
Authors’ reply Vincent van Hees raises an excellent point—that measurement of physical activity is complex. However, our overarching intent in The Lancet’s physical activity Series was to draw attention to the high prevalence of
inactivity worldwide, its determinants, harms, and intervention strategies, and to issue a call for global action at a time when many people were likely to think about physical activity: the 2012 summer Olympic Games. A detailed discussion of issues around measurement of physical activity, although extremely important, was not our goal. Although limitations remain in currently used methods of physical activity assessment, we prefer to see the glass as half full, not half empty. First, global surveillance of physical activity has progressed substantially, as shown in the first paper in our series.1 We were able to analyse comparable adult data from 122 countries and adolescent data from 105 countries. If we remind ourselves that no standardised instrument was used internationally 15 years ago, this is a great achievement. Second, assessment of other health behaviours, such as diet, are as challenging as assessment of physical activity.2 Discussions around the validity of available instruments are also seen in the published studies on smoking,3 owing to the possibility of underreporting. Third, we believe that finding a gold-standard measure of physical activity is a long-term goal, whereas current monitoring is sufficiently accurate to identify the magnitude of physical inactivity, sufficient to warrant a much greater focus on inactivity in non-communicable diseases prevention efforts. Additionally, we must also remind ourselves that instruments such as the international physical activity questionnaire and the global physical activity questionnaire were created for population-level surveillance purposes, and not for classification of “active or inactive” at the individual level. Furthermore, the data presented in our Series are based on self-report, and are unlikely to affect participants’ behaviours. With regard to the issue of reactivity with the use of objective monitors for physical activity, some
Corbis
Correspondence
For the Series on physical activity see http://www. thelancet.com/series/physicalactivity
1555
*Chi Pang Wen, Min Kuang Tsai, Xifeng Wu [email protected] Institute of Population Health Sciences, National Health Research Institutes, Zhunan, Miaoli County 350, Taiwan (CPW, MKT); China Medical University Hospital, Taichung, Taiwan (CPW, MKT); and Department of Epidemiology, MD Anderson Cancer Center, Houston, TX, USA (XW) 1
2
3
4
5
Wen CP, Wu X. Stressing harms of physical inactivity to promote exercise. Lancet 2012; 380: 192–93. World Lung Foundation and American Cancer Society. The tobacco atlas: harm from smoking. http://www.tobaccoatlas.org/harm/harm_ from_smoking/text/ (accessed Sept 18, 2012). WHO. WHO FCTC health warnings database. http://www.who.int/tobacco/ healthwarningsdatabase/en/index.html (accessed Sept 17, 2012). WHO, Research for International Tobacco Control. WHO report on the global tobacco epidemic, 2008: the MPOWER package. Geneva: World Health Organization, 2008. Wen CP, Wai JP, Tsai MK, et al. Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. Lancet 2011; 378: 1244–53.
www.thelancet.com Vol 380 November 3, 2012
The challenge of assessing physical activity in populations In your Series on physical activity (July 21) I believe that the challenge of measuring physical activity should have been given more attention. Most of the data presented in the Series are based on estimates of time spent in intensity levels. Nevertheless, no gold standard exists for the measurement of time spent in intensity levels in a reallife environment in a representative sample of the population and in a way that does not interfere with the behaviour of the study participants. As a consequence, the accuracy of both questionnaires and accelerometry to estimate time spent in intensity levels during daily life cannot be assessed. In other words, these physical activity data come with a measurement error that cannot be quantified. A similar problem applies to counting steps per day with pedometers. The problem described above complicates both innovation of measurement techniques and interpretation of the collected data. Reconsideration of what it is that we want to measure might be necessary. Paradoxically, however, methodological innovation is impossible without violation of methodological consistency, yet both are needed for reliable physical activity research. I declare that I have no conflicts of interest.
Vincent van Hees [email protected] Movelab, Institute of Cellular Medicine, Newcastle University, Newcastle-upon-Tyne NE2 4HH, UK; and MRC Epidemiology Unit, Institute of Metabolic Science, Cambridge, UK
Authors’ reply Vincent van Hees raises an excellent point—that measurement of physical activity is complex. However, our overarching intent in The Lancet’s physical activity Series was to draw attention to the high prevalence of
inactivity worldwide, its determinants, harms, and intervention strategies, and to issue a call for global action at a time when many people were likely to think about physical activity: the 2012 summer Olympic Games. A detailed discussion of issues around measurement of physical activity, although extremely important, was not our goal. Although limitations remain in currently used methods of physical activity assessment, we prefer to see the glass as half full, not half empty. First, global surveillance of physical activity has progressed substantially, as shown in the first paper in our series.1 We were able to analyse comparable adult data from 122 countries and adolescent data from 105 countries. If we remind ourselves that no standardised instrument was used internationally 15 years ago, this is a great achievement. Second, assessment of other health behaviours, such as diet, are as challenging as assessment of physical activity.2 Discussions around the validity of available instruments are also seen in the published studies on smoking,3 owing to the possibility of underreporting. Third, we believe that finding a gold-standard measure of physical activity is a long-term goal, whereas current monitoring is sufficiently accurate to identify the magnitude of physical inactivity, sufficient to warrant a much greater focus on inactivity in non-communicable diseases prevention efforts. Additionally, we must also remind ourselves that instruments such as the international physical activity questionnaire and the global physical activity questionnaire were created for population-level surveillance purposes, and not for classification of “active or inactive” at the individual level. Furthermore, the data presented in our Series are based on self-report, and are unlikely to affect participants’ behaviours. With regard to the issue of reactivity with the use of objective monitors for physical activity, some
Corbis
Correspondence
For the Series on physical activity see http://www. thelancet.com/series/physicalactivity
1555