The benefits of physical activity are wide ranging and associated with reduced disease risk and improved mental health. Strong evidence from high-income countries (HICs) has revealed a clear dose–response relationship between physical activity and improved health status. Regular physical activity is associated with a reduced risk of coronary heart disease, high blood pressure, stroke, metabolic syndrome, type 2 diabetes, breast and colon cancer, depression and dementia. Similarly, in low-income and middle-income countries (LMICs), higher physical activity levels are associated with a lower risk of cardiovascular disease and mortality. Physical activity has also been associated with improved mental health outcomes and increased self-esteem, self-efficacy and social capital; however, the direction and strength of these relationships needs further investigation to fully understand the impact of physical activity on mental well-being.This work was funded by http://dx.doi.org/10.13039/100004440 Wellcome Trust (grant number: 206194), National Institute for Health Research Cambridge Biomedical Research Centre (UK) http://dx.doi.org/10.13039/501100000265 and the African Partnership for Chronic Disease Research (Medical Research Council UK partnership grant number MR/K013491/1)

Barr, Anna Louise

Sandhu, Manjinder S

Young, Elizabeth H

Apollo (Cambridge)

 1Barr AL, et al. BMJ Glob Health 2018;3:e001044. doi:10.1136/bmjgh-2018-001044Objective measurement of physical activity: improving the evidence base to address non-communicable diseases in AfricaAnna Louise Barr,1 Elizabeth H Young,1,2 Manjinder S Sandhu1,2CommentaryTo cite: Barr AL, Young EH, Sandhu MS. Objective measurement of physical activity: improving the evidence base to address non-communicable diseases in Africa. BMJ Glob Health 2018;3:e001044. doi:10.1136/bmjgh-2018-001044Handling editor Seye AbimbolaReceived 9 July 2018Revised 31 August 2018Accepted 15 September 20181Department of Medicine, University of Cambridge, Cambridge, UK2Wellcome Sanger Institute, Genome Campus, Hinxton, UKCorrespondence toDr Manjinder S Sandhu;   ms23@ sanger. ac. uk© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY. Published by BMJ.Summary box ► Physical inactivity is one of the major modifiable risk factors for non-communicable diseases (NCDs). ► African countries, many of which are in the early stages of an emerging NCD epidemic, have the op-portunity to reduce the financial and health burden of NCDs through the early implementation of preven-tion strategies that promote physical activity. ► The design and success of physical activity promo-tion strategies requires an improved understanding of the physical activity patterns of African popula-tions and their multiple determinants. ► Integrating objective physical activity measurement devices within research and routine surveillance infrastructures in Africa would improve the quality, coverage and resolution of physical activity data on the continent and inform the design and implemen-tation of effective policies and interventions for the local context. ► This framework also permits the monitoring of pop-ulation physical activity patterns and trends, as well as the evaluation of interventions at the individual and population level.InTroduCTIonThe benefits of physical activity are wide ranging and associated with reduced disease risk and improved mental health. Strong evidence from high-income countries (HICs) has revealed a clear dose–response relation-ship between physical activity and improved health status. Regular physical activity is asso-ciated with a reduced risk of coronary heart disease, high blood pressure, stroke, meta-bolic syndrome, type 2 diabetes, breast and colon cancer, depression and dementia.1 2 Similarly, in low-income and middle-income countries (LMICs), higher physical activity levels are associated with a lower risk of cardi-ovascular disease and mortality.3 Physical activity has also been associated with improved mental health outcomes and increased self-es-teem, self-efficacy and social capital; however, the direction and strength of these relation-ships needs further investigation to fully understand the impact of physical activity on mental well-being.4Global burden of pHySICal InaCTIvITyGuidelines on the total volume of phys-ical activity required to reduce the risk of specific NCDs are imprecise; however, the WHO recommends that adults undertake at least 150 min of moderate-intensity physical activity per week, or 75 min of vigorous-inten-sity physical activity per week, to reduce the overall risk of NCDs.1 Worldwide 23.3% of adults do not meet these recommendations and are considered physically inactive.2 Low physical activity was identified as one of the leading risk factors responsible for the global disease burden, with an estimated 1.4 million deaths attributed to low physical activity in 2016, an increase of 18.4% since 2006.5 The disease burden is especially high in LMICs, with 75% of the estimated 13.4 million disa-bility-adjusted life years lost to physical inac-tivity in 2013 attributed to these regions.6 In the same year, physical inactivity was esti-mated to have cost global healthcare systems international $ 53.8 billion.6burden of pHySICal InaCTIvITy In afrICaAfrica is a region in transition. The demo-graphic profile of the continent is changing: reductions in infant and child mortality have contributed to rapid population growth and a concomitant rise in life expectancy. Africa is also the fastest urbanising continent, with the number of people living in urban areas projected to triple in the next 50 years.7 Globalisation, technological advances and  on 4 April 2019 by guest. Protected by copyright.http://gh.bmj.com/BMJ Glob Health: first published as 10.1136/bmjgh-2018-001044 on 8 October 2018. Downloaded from 2 Barr AL, et al. BMJ Glob Health 2018;3:e001044. doi:10.1136/bmjgh-2018-001044BMJ Global Healtheconomic development have all contributed to a trend towards sedentary lifestyles and the uptake of unhealthy behaviours on the continent. These demographic, social and environmental changes have led to an emerging NCD epidemic, complicated by an existing high preva-lence and incidence of chronic infectious diseases such as tuberculosis, malaria and HIV. Physical activity is influ-enced by a complex interaction of biological, social and environmental factors. As such, the distribution and determinants of physical inactivity, and its relative contri-bution to the burden of NCDs, will likely differ within and between African countries at varying stages of economic development and with diverse sociocultural contexts. A meta-analysis of self-reported physical activity data from 22 African countries found 16% of men and 24% of women were physically inactive, which is comparable to prevalences reported in HICs.8 However, the prevalence of physical inactivity varied between countries, ranging from 46.2% of men and 60.3% of women in Mali to 3.8% of men and 4.2% of women in Mozambique.8 The source of this variation is not well understood, but differences in body mass index, perceptions of body image, socio-economic status, urbanicity, safety, security and access to spaces that support physical activity are likely to be contributing factors.9–15MeTHodS To MeaSure pHySICal aCTIvITyCurrent epidemiological evidence on the physical activity patterns of African populations and their relationship to NCDs is largely based on self-report questionnaires and a small number of studies using objective measurement devices. While self-report questionnaires are the most popular tool used to measure physical activity, particu-larly at scale, their validity often tends to be moderate-to-poor due to their reliance on participants accurately reporting their physical activity patterns.16 Discrepancies have previously been found between objectively meas-ured and self-reported data. In one study conducted in the Seychelles, Ghana and South Africa, all men reported accumulating over 60 min of moderate-to-vigorous phys-ical activity per day; however, when compared with accel-erometery data only 32%, 56% and 58% of men accumu-lated 30 min or more of physical activity per day in each respective country.17 The differences for women were even greater.17 Furthermore, lower education may be associated with reduced reliability and validity estimates for certain physical activity measures in LMICs.18 19 Objec-tive physical activity monitors, meanwhile, permit contin-uous data collection in real-life conditions at greater resolution for longer periods of time, improving the volume and accuracy of data available. Objective meas-urement devices, designed for academic purposes, have been used in large-scale population studies in HICs for over a decade, while commercial physical activity trackers and smart phone applications are increasingly being used in clinical trials and National Institutes of Health funded research.20 An optional protocol for the objective measurement of physical activity is being incorporated in the WHO STEPwise Approach to Chronic Disease Risk Factor Surveillance data collection tool, signalling the broad acceptance that these devices are an important resource in the epidemiologists’ toolkit.IMprovInG our evIdenCe baSe THrouGH THe objeCTIve MeaSureMenT of pHySICal aCTIvITyThe limitations of self-report data currently restrict our ability to accurately characterise the dose–response rela-tionship between physical activity and disease risk in these populations. Meanwhile, the technology of objective meas-urement devices is constantly evolving: manufacturers are continually refining device algorithms to improve activity pattern recognition, increasing our ability to delineate the health benefits of specific activities.9 Our knowledge of the social, biological and environmental determinants of physical activity in Africa, including the impact of urbanisation and economic development, is limited by the need for context-specific measures for these determi-nants and the paucity of longitudinal data to determine causation.21 Smart phone ownership in Africa is acceler-ating: a median of 33% reported owning a smart phone in 2018, with a 14%–15% increase in ownership reported in Senegal, South Africa and Ghana between 2015 and 2017.22 This and the increasing availability of commer-cial physical activity monitors presents an opportunity to harness physical activity data collected as users carry out their daily lives.22 With careful consideration of ethical, data privacy and security issues, these devices have the potential to facilitate routine surveillance and moni-toring of population physical activity patterns and trends, as well as evaluating clinical, societal and environmental interventions at the individual and population level.opporTunITy for InTervenTIonThe majority of African countries have a policy or strategy which addresses physical inactivity, but only 70% report that these are operational,23 and evidence of effective-ness is scarce, partly due to the limited surveillance of physical activity across the continent. Integrating active living and sports programmes within schools and work places is a strategy advocated by global policy makers and a recommended ‘best buy’ intervention for the preven-tion and control of the global NCD pandemic.24 Like-wise, creating environments which support the integra-tion of physical activity into people’s daily lives through active travel or leisure activity is highly recommended.25 However, evidence of effective and sustainable inter-ventions to increase physical activity at the population level within these settings is limited. Furthermore, the observed benefits of such interventions may not transfer directly to the African context. The unprecedented, and often uncontrolled, growth in urbanisation on the conti-nent calls for urgent and innovative urban planning poli-cies that support an active population. on 4 April 2019 by guest. Protected by copyright.http://gh.bmj.com/BMJ Glob Health: first published as 10.1136/bmjgh-2018-001044 on 8 October 2018. Downloaded from Barr AL, et al. BMJ Glob Health 2018;3:e001044. doi:10.1136/bmjgh-2018-001044 3BMJ Global HealthUsing context-specific data on population activity levels and their social and environmental determinants in the design and implementation of policies ensures they address the specific needs of populations in these regions. Similarly, integrating objective measurement of physical activity patterns and trends within research and surveillance infrastructure will be integral to improving the evidence base for policy development and the effec-tive evaluation of these interventions at the population level. The success of such interventions will likely require engagement with education, commercial, urban plan-ning, transportation, environmental and sports and recreation sectors. Consideration of individual-level factors such as wearer compliance and participation, as well as broader environmental issues such as climate, geography, safety and security will be necessary for the long-term sustainability of these interventions.9 12 20 21 25 Capacity building initiatives and financial support will also be integral to the widespread deployment of objec-tive measurement devices. Finally, physical activity inter-ventions should be integrated within a broader NCD prevention strategy addressing NCD risk factors such as diet, smoking and alcohol consumption.ConCluSIonAfrican countries are in a position to reduce the finan-cial and health burden of the burgeoning NCD epidemic through the early implementation of prevention strat-egies targeting modifiable risk factors such as physical inactivity. Encouraging populations to regularly under-take physical activity requires a cultural shift: the bene-fits of physical activity to health and well-being need to be valued by both individuals and civil society. Govern-ments and industrial partners have a pivotal role to play in realising these societal changes by adopting social and environmental policies and interventions that promote physical activity. Investing in objective measurement tools and physical activity surveillance infrastructure would improve the quality and coverage of physical activity data and ensure that clinical and public health decision making is guided by the best available evidence.Contributors ALB, EHY, MSS: conceived the commentary. ALB: drafted the manuscript. All authors were involved in the writing of the manuscript at revision stages and have read and approved the final version.funding This work was funded by http:// dx. doi. org/ 10. 13039/ 100004440 Wellcome Trust (grant number: 206194), National Institute for Health Research Cambridge Biomedical Research Centre (UK) http:// dx. doi. org/ 10. 13039/ 501100000265 and the African Partnership for Chronic Disease Research (Medical Research Council UK partnership grant number MR/K013491/1).Competing interests None declared.patient consent Not required.provenance and peer review Not commissioned; externally peer reviewed.data statement No data to share.open access This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: http:// creativecommons. org/ licenses/ by/ 4.0RefeRenCes 1. World Health Organization. Global recommendations on physical activity for health. Geneva: WHO, 2010. 2. Sallis JF, Bull F, Guthold R, et al. Progress in physical activity over the olympic quadrennium. Lancet 2016;388:1325–36. 3. Lear SA, Hu W, Rangarajan S, et al. The effect of physical activity on mortality and cardiovascular disease in 130 000 people from 17 high-income, middle-income, and low-income countries: the PURE study. Lancet 2017;390:2643–54. 4. Mason OJ, Holt R. Mental health and physical activity interventions: a review of the qualitative literature. J Ment Health 2012;21:274–84. 5. Vos T, Abajobir AA, Abate KH, et al. Global, regional, and national incidence, prevalence, and years lived with disability for 328 diseases and injuries for 195 countries, 1990-2016: a systematic analysis for the global burden of disease study 2016. Lancet 2017;390:1211–59. 6. Ding D, Lawson KD, Kolbe-Alexander TL, et al. 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The toronto charter for physical activity: a global call for action. http://www. paha. org. uk/ Resource/ toronto- charter- for- physical- activity- a- global- call- for- action on 4 April 2019 by guest. Protected by copyright.http://gh.bmj.com/BMJ Glob Health: first published as 10.1136/bmjgh-2018-001044 on 8 October 2018. Downloaded from 

Objective measurement of physical activity: improving the evidence base to address non-communicable diseases in Africa.

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Objective measurement of physical activity: improving the evidence base to address non-communicable diseases in Africa.

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