Introduction

Leisure-time physical activity (LTPA) can be defined as volitional activity obtained through participation in sports, exercise and recreation at a moderate and/or vigorous intensity level, independent of other key physical activity (PA) domains, i.e., active transport (purposeful walking or cycling), domestic and occupational activity [1], [2]. In most high-income nations, modern technology and amenities have reduced the necessity for regular higher-level intensity activity via housework, physically demanding occupations, and active transport [3]. This is reflected in time-trend data showing declines in the average amount of time spent in domestic and work activity domains over recent decades [4], [5]; trends in active transport have been mixed, indicating both a decline [4] and an increase in this domain [6], [7]. Unlike other domains, time spent in LTPA has either remained stable [7], [8] or increased in several countries [2], [6], including the United Kingdom (UK) [9], [10]. Despite this population-level increase in LTPA, the proportion of UK adults meeting the minimum recommended PA guidelines (≥30 minutes of moderate or vigorous intensity PA on ≥5 days a week) was low in the Health Survey for England 2008 [10], [11]. Among older (≥65 years) UK adults, only 16% of men and 12% of women met the guidelines [10], [11], with exercise and fitness activities constituting only a small proportion of time spent in moderate-to-vigorous PA [11]. Data from Sport England's 2012/13 Active People Survey suggest that, of English adults aged 55–64 and ≥65 years, 61.6% and 73.9%, respectively, do not play any sports [12]. However, to achieve recommended levels of PA, LTPA is thought to be the domain most amenable to intervention especially in later life because other domains (e.g. occupational activity) are unlikely to be viable targets due to factors including retirement. Medical and public health professionals, as well as policymakers, have therefore focused intently on increasing the levels of activity obtained through LTPA at all ages, including older adults, in efforts to improve population health [13], [14].

Physical inactivity is associated with increased risk of numerous chronic conditions, cognitive decline and physical disability, as well as premature mortality [15]–[19]. Given the health benefits of PA, previous research has explored and identified numerous real and/or perceived personal and environmental barriers to initiating and maintaining PA [20], [21]. In older adults, barriers to PA can include current health status, availability of social support, and access to safe and affordable resources [21]–[24]. Additionally, a narrower range of different types of LTPAs may be acceptable and/or feasible in older adults because of increasing chronic disease burden and perceived and real injury risk. To help health promotion programs to be successful in improving levels of LTPA, it may also be useful to examine what sports and exercises adults in early old age organically engage in during their leisure-time, identifying the types and diversity of activity that are most acceptable and therefore potentially amenable to intervention.

Only a few nationally representative studies have examined the type and diversity of LTPA self-reported by community-dwelling older adults. Walking for exercise was the most commonly reported LTPA among older Americans (≥60 years) [25], Australians (≥65 years) [26], European Union citizens (≥55 years) [3], and English adults (≥65 years) [11]. After walking, activities such as cycling, golf, aerobics, swimming/water sports, and stretching were most often reported [3], [25]. Less than a third of older Australians reported two or more LTPA activities and only 2.6% reported engaging in a combination of aerobic, balance and flexibility exercises, as well as strength activities [26].

Health promotion programs also need to take account of how gender and obesity may influence type and diversity of LTPA. Studies of younger adults have highlighted notable gender differences in LTPA type, with men engaging in sports, jogging/running, cycling, and golf more often than women [27]–[29], however gender differences may change with increasing age. Previous research suggests that non-obese individuals are more likely to engage in LTPA than obese individuals [3], [29] but it is less clear whether type and diversity of activity are also influenced by obesity status in older age.

The aim of this study was to use data from the Medical Research Council (MRC) National Survey of Health and Development (NSHD) (1946 British Birth Cohort) to describe the types and diversity of leisure-time sports and exercise activities that adults aged 60–64 years report undertaking by gender and obesity status.

Particpants And Methods

Results

The percentage of participants reporting participation in each sport and exercise activity in the past year, as well as the mean number of minutes per week participants reported undertaking an activity are given in Table 1. Overall, 71% of participants reported walking for pleasure in the past year for an average of 192.7 minutes per week. Other activities were less frequently reported; the top 10 most commonly reported activities in the last year were swimming (33%), floor exercises (24%), conditioning exercises (16%), cycling (15%), backpacking/hill-walking (14%), dancing (14%), golfing (12%), exercises with weights (11%), and aerobics (8%). Walking for pleasure was also the most common activity reported on a regular basis (≥30 minutes per week), as it was reported by 59% of women and 52% of men (test of gender difference, p = 0.002). While similarities existed between men and women with regard to the top 10 activities reported on a regular basis, gender differences were observed in the percentage of individuals reporting each given activity. Briefly, women more often participated in walking for pleasure, swimming, aerobics, floor exercises, and dancing on a regular basis (Figure 1), whereas men more often engaged in backpacking/hill-walking, jogging and running, cycling and golfing.

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Figure 1. The percentage (%) of participants, (n^§ = 2188) reporting sport and exercise activities on a regular basis^‡, by gender.

^§ Percentages reported are based on available n for each specific activity; ^‡‘report of weekly participation in ‘x’ activity of minimum duration, 30 minutes per episode’. ^*p<0.05; ^‡p<0.10: test of gender difference. Note: No difference by gender existed for exercises with weights and conditioning exercises either in the last year or report of regular participation; N's were not robust to examine football, horse-riding, cricket, ice-skating, martial arts, and netball by gender due to low number of participants reporting these activities. Activity order was determined by the most frequent activity in both genders combined. Top ten most frequently reported activities by gender (where ‘1’ indicates most frequently reported activity): Men: 1) walking for pleasure, 2) golfing, 3) floor exercises, 4) backpacking/hill-walking, 5) conditioning exercises, 6) cycling, 7) swimming, 8) exercises with weights, 9) fishing and 10) snooker. Women: 1) walking for pleasure, 2) floor exercises, 3) swimming, 4) conditioning exercises, 5) aerobics, 6) dancing, 7) backpacking/hill-walking, 8) exercises with weights, 9) golfing and 10) cycling.

https://doi.org/10.1371/journal.pone.0098901.g001

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Table 1. The percentage (%) of participants reporting each sport and exercise activity in the past year and mean (SD) time (minutes per week) spent in each activity.

https://doi.org/10.1371/journal.pone.0098901.t001

Among men (Figure 2A), the top 10 regular reported activities were similar by obesity status, however differences were observed in the percentage of individuals reporting each given activity. A greater percentage of non-obese men regularly engaged in walking for pleasure (55% vs. 46%, p = 0.02) and floor exercises (12% vs. 5%, p = 0.002) than obese men. A trend for non-obese men to more often report cycling (8% vs. 5%, p = 0.08) than obese men was also observed. Similar to men, among women the top 10 regular activities were comparable by obesity status but again differences were observed in the reported percentages. Among women (Figure 2B), those who were non-obese more often reported regularly walking for pleasure (64% vs.47%, p<0.001), engaging in floor exercises (23% vs. 17%, p = 0.02), as well as backpacking/hill-walking (7% vs. 3%, p = 0.01), and golfing (5% vs 2%, p = 0.01) when compared to obese women. However, obese women more frequently reported taking part in conditioning exercises (12% vs. 8%, p = 0.04) than non-obese women.

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Figure 2. The percentage (%) of men (n^§ = 1046) and women (n^§ = 1142) reporting sport and exercise activities on a regular basis^‡, by obesity status.

^§ Percentages reported are based on available n for each specific activity; ^‡‘report of weekly participation in ‘x’ activity of minimum duration, 30 minutes per episode’. ^*p<0.05; ^‡p<0.10: test of difference by obesity status. (A) Activity order was determined by the most frequent activity among men. Top ten most frequently reported activities among men (where ‘1’ indicates most frequently reported activity): BMI<30 kg/m²: 1) walking for pleasure, 2) golfing, 3) floor exercises, 4) backpacking/hill-walking, 5) conditioning exercises, 6) cycling, 7) swimming, 8) fishing, 9) exercises with weights and 10) snooker. BMI≥30 kg/m²: 1) walking for pleasure, 2) golfing, 3) conditioning exercises, 4) backpacking/hill-walking, 5) fishing, 6) exercises with weights, 7) swimming, 8) floor exercises, 9) sailing and 10) cycling. (B) Activity order was determined by the most frequent activity among women. Top ten most frequently reported activities among women (where ‘1’ indicates most frequently reported activity): BMI<30 kg/m²: 1) walking for pleasure, 2) floor exercises, 3) swimming, 4) aerobics, 5) conditioning exercise, 6) dancing,7) backpacking/hill-walking, 8) exercises with weights, 9) golfing and 10) cycling. BMI≥30 kg/m²: 1) walking for pleasure, 2) floor exercises, 3) swimming, 4) conditioning exercise, 5) aerobics, 6) exercises with weights, 7) dancing, 8) bowling, 9) backpacking/hill-walking and 10) cycling.

https://doi.org/10.1371/journal.pone.0098901.g002

Overall, 16% of participants reported no engagement in any of the activities at least once within the past year, while approximately 21% engaged in one, 19% in two, 15% in three and 28% in four or more activities; the distribution across groups was comparable by gender (p = 0.2) (Table 2). When restricting analyses to activities participants engaged in on a regular basis, there was less activity diversity; nearly 27% of participants reported no regular engagement in any of the activities, 34% reported one activity, 20% reported two, 11% reported three, and just 9% of participants reported regular engagement in four or more different activities. Diversity of regular activity was comparable by gender (p = 0.9). The majority of activity was classified as cardio-respiratory and the percentage engaging in cardio-respiratory activity was comparable by gender, both at least once throughout the year (p = 0.2) and on a regular basis (p = 0.3). However, when compared to men, women were more likely to engage in activities beneficial for balance and flexibility at least once throughout the year and on a regular basis (both p<0.001). A lower percentage of men and women engaged in all combinations of activity on a regular basis than at any point throughout the year. When compared to men, women were more likely to engage in all combinations of activity at least once throughout the year (p = 0.02) and on a regular basis (p = 0.04).

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Table 2. Diversity in leisure-time physical activity and participation in different activity-types, % (CI), by gender and obesity status.

https://doi.org/10.1371/journal.pone.0098901.t002

BMI was associated with both activity diversity and activity type for both men and women (Table 2). A greater percentage of non-obese men reported engaging in four or more activities, while a greater percentage of obese men reported no participation in any of the activities at any point throughout the year (p = 0.03). Diversity was not significantly associated with obesity status among men when examining activity on a regular basis (p = 0.3), though trends remained. In women, however, diversity of activity was associated with obesity status both throughout the year and on a regular basis (both p<0.001). When examining the activity type reported, a greater percentage of non-obese men and women reported cardio-respiratory activity at some point throughout the year (p = 0.01 and p<0.001, respectively) and on a regular basis (p = 0.02 and p<0.001, respectively), than did obese participants. In addition, a greater percentage of non-obese men also reported activities beneficial for balance and flexibility at some point throughout the year (p = 0.04), as well as on a regular basis (p = 0.01). This was also observed among women throughout the year (p = 0.03), as well as on a regular basis (p = 0.01). No difference was observed by BMI status for participation in activities beneficial for strength or all combinations of activities among men and women (all p>0.05).

Discussion

Using data from a nationally representative study, we have characterized the types and diversity of LTPA that British adults in early old age reported undertaking in the past year. We found gender differences, as well as differences by obesity status, in the activities reported, the levels of activity diversity and activity types. Walking for pleasure was the most commonly reported LTPA among both men and women, and these findings are consistent with the literature [3], [11], [25], [26]. In addition to walking, we found that 62% of participants reported diversity (i.e. ≥2 unique activities) of leisure-time activities at least once throughout the year, but only 40% reported doing so on a regular basis. Levels of participation diversity were higher in this study than previously reported in a sample of older Australians (≥65years) [26].

There were gender differences found in the activities reported. Among the list of the top 10 activities undertaken on a regular basis, a greater percentage of men reported golfing, cycling, and backpacking/hill-walking, whereas more women reported walking for pleasure, floor exercises, aerobics, dancing and swimming. The activities men more often reported engaging in are of greater intensity and have higher associated metabolic equivalent (MET) values [35], [36] yet high-impact team activities (e.g. football) that are often popular in earlier adulthood, especially among men [28], are noticeably absent from the top 10 list in this study. Indeed, football was one of the most frequently reported activities among men in the NSHD at age 36 years [37]. Swimming (in both sexes) and golf (in men) were among the most frequently reported activities at both ages [37], suggesting that such lower intensity activities may be more likely to be maintained with increasing age than more vigorous activities such as football and running. That more of the activities frequently reported among women at age 36 years (e.g. swimming and dancing) were also in the top 10 most frequently reported activities at age 60–64 years [37], suggests that greater changes in activity type may occur among men than women with increasing age.

Study results also suggest that activity diversity and activity type varied by obesity status among men and women. Non-obese women reported greater activity diversity on a regular basis than obese women, though this relationship was not observed among men. These results are in line with findings from a Canadian study that found the prevalence of physical inactivity increased with increasing BMI among women, but not in men and that the largest difference between BMI status occurred among the oldest age group (50–64 years) [38]. In the current study, lower BMI was associated with more regular participation in cardio-respiratory activity, as well as balance and flexibility activity for both men and women. To our knowledge, this study is the first to examine the relationship between leisure-time sport and exercise activity, gender and BMI in this way. Despite different PA measurement and operationalization (e.g., leisure METS), our findings are also supported by prior research suggesting an association between higher levels of recreational activity and lower BMI, as well as no association for vigorous active recreation (time spent in any activity of ≥5METS) among men by BMI status [29].

Although walking is often recommended to adults, especially those overweight and/or older, as a way to increase PA levels through low-impact activity, our study found that regular weekly walking for pleasure varied by BMI status among both men and women. This difference was not observed among another low-impact activity, swimming, which is commonly recommended to older and/or overweight populations as a low weight-bearing, joint-friendly activity [39], [40]. While the difference in reports observed by BMI status may reflect lower BMI as a result of regular walking for pleasure during one's lifetime or adulthood, our findings may also indicate that obese individuals face additional barriers to walking for pleasure (e.g. pain, physical disability, embarrassment) that go beyond, but are also related to body size and weight [41]. Indeed, findings from the EPIC-Norfolk cohort suggest that weight status and weight gain are associated with both contemporaneous levels and subsequent changes in physical inactivity [42]. Combined with findings from the current study, this may suggest that the benefits of walking should be promoted within a context that acknowledges personal, social, and/or environmental barriers among older adults with higher BMI, so as to increase engagement in walking for pleasure as a LTPA and reduce the observed difference by BMI status.

Previous research has found that, in contrast to domestic activities, leisure pursuits, outdoor pursuits, sports (team and non-team), and exercise and fitness contributed very little towards the proportion of total time per week spent in moderate-to-vigorous physical activity among English adults aged 65 years and older [11]. We extend these observations through our examination of diversity and activity type in the current study. While fewer than 10 percent of older adults reported high activity diversity, i.e. four or more different leisure sport and exercise activities on a regular basis, nearly a third were found to have high diversity throughout the year. Seasonality of activity participation may play a role in the finding of higher diversity when considering activity undertaken at any point throughout the year, as some activities can only be undertaken in specific seasons and better conditions exist for many activities (e.g., reduced access/transportation barriers, increased daylight, fairer weather conditions), especially those conducted outdoors, in spring and summer. However, these findings do suggest that older adults have varied activity interests and that there may be great potential for increasing the time older adults spend in sport and exercise activities by encouraging regular participation in a variety of diverse activities. That nearly 60 percent of participants reported either none or participation in just one of the activities on a regular basis represents an opportunity for public health practitioners and clinicians to discuss and encourage older adults to increase their PA through a varied and diverse routine of sport and exercise activities. Engagement in a greater number of different activities may be a strategy that results in greater time spent in overall activity, especially for older adults who are either overweight or obese.

Our study has several strengths. It is a nationally representative sample of adults in early old age, with good characterization of LTPA as measured by a validated questionnaire, the EPAQ2. However, some limitations should be noted. In general, self-report PA, as measured by questionnaire, is noted to suffer from recall bias, especially among older adults [43]–[45]. For example, participants may have difficulty remembering whether or not they engaged in a particular activity in the past, as well as the average length of time per episode. Self-report PA is also prone to social desirability bias, as participants might feel compelled to over-report activity levels knowing the benefits of PA on health. However, self-reported questionnaires are currently the best method for ascertaining information on participation in different types of activity, as these parameters of PA are not yet easily captured by objective monitoring. Further, we purposefully chose to focus on sport and exercise activities that are of higher intensity (moderate-to-vigorous) partly because they are reported with greater reliability and validity than lower intensity (light) activities [46], [47]. Additionally, higher intensity activities are often thought to enable older adults to meet the currently recommended PA levels. We were unable to explore reasons for choice of activity and explanations of non-participation, as we did not ask participants whether or not non-participation or low participation frequency was due to lack of interest, lack of opportunity/resources, or physical inability to engage in a specific activity. Nor did we ask participants if they independently engaged in an activity, if they were active with a group or someone in their social network, or even their preference for solo or group activity. Therefore, we suggest that these factors are explored in future research, as well as in advance of development/implementation of interventions to increase PA among older men and women.

Conclusion

In conclusion, there is considerable variation in types and diversity of leisure sports and exercise activities in this population of British adults in early old age, and different patterns of activity were observed by gender and obesity status. While 40 percent engaged in two or more types of activity on a regular basis, the majority reported no diversity or regular participation in any of the activities queried. In general, walking for pleasure is the activity most often reported among older adults, perhaps due in part to its ease, convenience, lack of associated risk and inexpensive nature, as well as perhaps increased likelihood of exposure to an outdoor environment. Clinicians, public health professionals and researchers might capitalize on this knowledge when developing trials of PA interventions tailored and targeted to older men and women, and those with high BMI.

Acknowledgments

The authors are grateful to NSHD study members who took part in this latest data collection for their continuing support. We thank Professor Michael Wadsworth, Suzie Clennell, and members of the NSHD scientific and data collection team at the following centres: MRC Unit for LHA, MRC Human Nutrition Research, Cambridge; MRC Epidemiology Unit, Cambridge; MRC Lifecourse Epidemiology Unit, Southampton; Wellcome Trust (WT) Clinical Research Facility (CRF) Manchester, the Manchester Heart Centre, and the Department of Clinical Radiology at the Central Manchester University Hospitals NHS Foundation Trust; WTCRF, Medical Physics and the Department of Cardiology at the Western General Hospital in Edinburgh; WTCRF, Department of Nuclear Medicine and the Department of Cardiology at University Hospital Birmingham; WTCRF and the Department of Nuclear Medicine at University College London Hospital; CRF, the Department of Medical Physics and the Department of Cardiology at the University Hospital of Wales; CRF and Twin Research Unit at St Thomas' Hospital London; Vascular Physiology Unit, Institute of Child Health, London; National Heart and Lung Institute, Imperial College London; Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow; Cardiovascular Institute, Sahlgrenska Academy, Gothenburg University; National Centre of Social Research (NatCen).

Members of the NSHD scientific and data collection teams (lead Diana Kuh; email: d.kuh@ucl.ac.uk) are:

Rachel Cooper (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Rebecca Hardy (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Diana Kuh (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Mary Pierce (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Marcus Richards (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Jane Abington (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Andrew Wong (MRC Unit for Lifelong Health and Ageing at UCL, London, UK), Judith E. Adams (Clinical Radiology, Manchester Royal Infirmary, Manchester, UK), Mike Machin (Clinical Radiology, Manchester Royal Infirmary, Manchester, UK), Alison M. Stephens (MRC Human Nutrition Research, Cambridge, UK), Kerina Bonar (MRC Human Nutrition Research, Cambridge, UK), Susan Bryant (MRC Human Nutrition Research, Cambridge, UK), Darren Cole (MRC Human Nutrition Research, Cambridge, UK), Wing Nip (MRC Human Nutrition Research, Cambridge, UK), Gina Ambrosini (MRC Human Nutrition Research, Cambridge, UK), Denis Pellerin (Department of Echocardiography, The Heart Hospital, London, UK), Nishi Chaturvedi (International Centre for Circulatory Health (ICCH), National Heart and Lung Institute, Imperial College London, London, UK), Alun Hughes (International Centre for Circulatory Health (ICCH), National Heart and Lung Institute, Imperial College London, London, UK), Arjun Ghosh (International Centre for Circulatory Health (ICCH), National Heart and Lung Institute, Imperial College London, London, UK), Katherine March (International Centre for Circulatory Health (ICCH), National Heart and Lung Institute, Imperial College London, London, UK), Peter Macfarlane (Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK), Louise Inglis (Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK), Peter Friberg (Cardiovascular Institute, Sahlgrenska University Hospital, Göteborg, Sweden), Walter Osika (Cardiovascular Institute, Sahlgrenska University Hospital, Göteborg, Sweden), Soren Brage (MRC Epidemiology Unit, Cambridge, UK), Ulf Ekelund (MRC Epidemiology Unit, Cambridge, UK), Stefanie Mayle (MRC Epidemiology Unit, Cambridge, UK), Kate Westgate (MRC Epidemiology Unit, Cambridge, UK), John Deanfield (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), Ann Donald (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), Sarah Kok (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), Stefano Masi (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), Ravneet Phalora (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), John Woodside (Vascular Physiology Unit, Institute of Child Health, University College London, London, UK), Ian Bruce (Wellcome Trust Clinical Research Facility, Manchester, UK), Nikki Harwood (Wellcome Trust Clinical Research Facility, Manchester, UK), Emma Oughton (Wellcome Trust Clinical Research Facility, Manchester, UK), Alison Chapman (Department of Clinical Radiology, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK), Rajdeep S Khattar (The Manchester Heart Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK), Satheesh Balakrishnan Nair (The Manchester Heart Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK), Jayne Franklyn (Wellcome Trust Clinical Research Facility, Birmingham, UK), Sue Palmer (Wellcome Trust Clinical Research Facility, Birmingham, UK), Karen Boardman (Wellcome Trust Clinical Research Facility, Birmingham, UK), Nicola Crabtree (Department of Nuclear Medicine, University Hospital Birmingham, Birmingham, UK), Ross Clements (Department of Cardiology, University Hospital Birmingham, Birmingham, UK), Michael Suvari (Department of Cardiology, University Hospital Birmingham, Birmingham, UK), Rick Steeds (Department of Cardiology, University Hospital Birmingham, Birmingham, UK), Kathrine Craig (Wellcome Trust Clinical Research Facility, Cardiff, UK), Emma Howard (Wellcome Trust Clinical Research Facility, Cardiff, UK), Terese Morley (Wellcome Trust Clinical Research Facility, Cardiff, UK), Maurice Scanlon (Wellcome Trust Clinical Research Facility, Cardiff, UK), Rebecca Petit (Department of Medical Physics, University Hospital of Wales, Cardiff, UK), Wil Evans (Department of Medical Physics, University Hospital of Wales, Cardiff, UK), Alan Fraser (Department of Cardiology, University Hospital of Wales, Cardiff, UK), Julie Edwards (Department of Cardiology, University Hospital of Wales, Cardiff, UK), Emma Reece (Department of Cardiology, University Hospital of Wales, Cardiff, UK), David Newby (Wellcome Trust Clinical Research Facility, Edinburgh, UK), Fiona Marshall (Wellcome Trust Clinical Research Facility, Edinburgh, UK), Jim Hannan (Department of Medical Physics, Western General Hospital, Edinburgh, UK), Carol Miller (Department of Medical Physics, Western General Hospital, Edinburgh, UK), Audrey White (Department of Cardiology, Western General Hospital, Edinburgh, UK), Raymond MacAllister (Wellcome Trust Clinical Research Facility, University College London, London, UK), Joanne Harris (Wellcome Trust Clinical Research Facility, University College London, London, UK), Roldan Singzon (Wellcome Trust Clinical Research Facility, University College London, London, UK), Peter Ell (Department of Nuclear Medicine, University College London Hospital, London, UK), Caroline Townsend (Department of Nuclear Medicine, University College London Hospital, London, UK), Camelia Demetrescu (Department of Echocardiography, The Heart Hospital, London, UK), Philip Chowienczyk (Wellcome Trust Clinical Research Facility, St. Thomas' Hospital, London, UK), Paula Darroch (Wellcome Trust Clinical Research Facility, St. Thomas' Hospital, London, UK), Karen McNeill (Wellcome Trust Clinical Research Facility, St. Thomas' Hospital, London, UK), Tim Spector (Twin Research Unit, St Thomas' Hospital, London, UK), Gail Clements (Twin Research Unit, St Thomas' Hospital, London, UK), Benyu Jiang (Twin Research Unit, St Thomas' Hospital, London, UK), Carli Lessof(NatCen, London, UK), Hayley Cheshire(NatCen, London, UK).