Screen-Based Sedentary Behavior, Physical Activity, and Muscle Strength in the English Longitudinal Study of Ageing

and Muscle Strength in the English Longitudinal Study of Ageing. PLoS ONE 8(6): e66222. doi:10.1371/journal.pone.0066222 Screen-Based Sedentary Behavior, Physical Activity, and Muscle Strength in the English Longitudinal Study of Ageing Mark Hamer 0 Emmanuel Stamatakis 0 Mel B. Feany, Brigham and Women's Hospital, Harvard Medical School, United States of America 0 1 Population Health Domain Physical Activity Research Group, University College London , London , United Kingdom , 2 Department of Epidemiology and Public Health, University College London , London , United Kingdom , 3 School for Physiology, Nutrition and Consumer Sciences, North-West University , Potchefstroom, South Africa, 4 Prevention Research Collaboration , School of Public Health, University of Sydney , Sydney , Australia Background: Sarcopenia is associated with loss of independence and ill-health in the elderly although the causes remain poorly understood. We examined the association between two screen-based leisure time sedentary activities (daily TV viewing time and internet use) and muscle strength. Methods and Results: We studied 6228 men and women (aged 64.969.1 yrs) from wave 4 (2008-09) of the English Longitudinal Study of Ageing, a prospective study of community dwelling older adults. Muscle strength was assessed by a hand grip test and the time required to complete five chair rises. TV viewing and internet usage were inversely associated with one another. Participants viewing TV $6hrs/d had lower grip strength (Men, B = 21.20 kg, 95% CI, 22.26, 20.14; Women, 20.75 kg, 95% CI, 21.48, 20.03) in comparison to ,2hrs/d TV, after adjustment for age, physical activity, smoking, alcohol, chronic disease, disability, depressive symptoms, social status, and body mass index. In contrast, internet use was associated with higher grip strength (Men, B = 2.43 kg, 95% CI, 1.74, 3.12; Women, 0.76 kg, 95% CI, 0.32, 1.20). These associations persisted after mutual adjustment for both types of sedentary behaviour. Conclusions: In older adults, the association between sedentary activities and physical function is context specific (TV viewing vs. computer use). Adverse effects of TV viewing might reflect the prolonged sedentary nature of this behavior. - Funding: National Institute on Aging in the United States (grants 2RO1AG7644-01A1 and 2RO1AG017644) and a consortium of UK government departments coordinated by the Office for National Statistics. MH is supported by the British Heart Foundation (RE/10/005/28296); ES is supported by a National Institute for Health Research Career Development Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Age related declines in muscle mass and strength, known as sarcopenia, are a risk factor for health and independence in the elderly. Measures of muscle strength have been associated with morbidity, functional independence and mortality in older populations [14] even after 25 yrs or more of follow-up. Several studies have documented associations between physical activity and muscle strength tests [5,6] and direct measures of lean mass [79] in older individuals, although the findings are not always consistent with some studies observing no associations [1012]. Inconsistencies in the data might be explained by different measures of physical activity (objective versus self-report) but also the failure to consider sedentary activities as an independent domain of behavior. Prolonged sedentary activities, particularly watching TV, have been associated with a range of adverse health outcomes independently from physical activity [1318]. Thus, sedentary behavior is now considered as a distinct domain of behavior, which may pose a risk to health in its own right. However, most research to date has focused on cardiometabolic and mortality outcomes but the independent role of sedentary behavior in explaining the declines in muscle strength with ageing remains unknown. Previous research suggests that not all types of sedentary behaviors are related with adverse health markers in elderly populations [19,20], thus it is unclear if the effects are being driven by physiological processes linked to excessive sitting or the specific and broader context of the activity. If associations are only apparent for specific types of sedentary activity this might suggest that residual confounding may be driving the effects. To test the overall hypothesis that excess screen-based sedentary behavior is inversely associated with muscle strength, we examined two types of common sedentary activities in relation to several key functionally relevant tests of physical performance. Ethics statement Participants gave full informed written consent to participate in the study and ethical approval was obtained from the London Multi-centre Research Ethics Committee. Study sample and procedures The English Longitudinal Study of Ageing (ELSA) is an ongoing cohort study that contains a nationally representative sample of the English population living in households [21]. The ELSA cohort consists of men and women born on or before 29 February 1952, using multistage stratified probability sampling with postcode sectors selected at the first stage and household addresses selected at the second stage. The data were collected by a team of trained researchers that adhered to strict protocols. For the purposes of the present analyses, data collected at wave 4 (2008-09) were used as this was the first occasion that information on sedentary activities was gathered. Sedentary and physical activity Participants were asked to recall How many hours of television do you watch on an ordinary day or evening, that is, Monday to Friday? and How many hours of television do you normally watch in total over the weekend, that is, Saturday and Sunday? Average daily time spent watching TV was calculated as {(weekday TV time x 5) + (Weekend TV time)}/7. Daily TV time was categorized into four groups (,2hrs/d; 2 to ,4 hrs/d; 4 to ,6hrs/d; $6 hrs/d). In addition participants were asked if they used a computer for internet or email. We have described the ELSA physical activity measurements in detail previously [22]. In brief, participants were asked how often they took part in three different types of physical activity: vigorous, moderate- and lowintensity physical activity. The response options were: more than once a week, once a week, one to three times a month and hardly ever/never. Physical activity was further categorized into three groups: None (no moderate or vigorous activity on a weekly basis); Moderate activity at least once a week; and Vigorous activity at least once a week. Physical strength measures Physical strength measures included hand grip and a timed chair stand test. Hand grip strength (kg) of the dominant hand was assessed using a hand held dynamom (...truncated)