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Age and Ageing 1998; 27-S3: 17-23 Stability and change in levels of habitual physical activity in later life GILLIAN K. ARMSTRONG, KEVIN MORGAN Centre for Ageing and Rehabilitation Studies, School of Health and Related Research, University of Sheffield, Northern General Hospital, Sheffield S5 7AU, UK Address correspondence to G. K. Armstrong. Fax: (+44) I 14 271 5771; E-mail: g.k.armstrong@sheffield.ac.uk Abstract Objectives: to describe stability and change in levels of customary physical act
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  Age and Ageing 1998; 27-S3: 17-23 Stability and change in levels ofhabitual physical activity in later life GILLIAN K. ARMSTRONG, KEVIN MORGANCentre for Ageing and Rehabilitation Studies, School of Health and Related Research, University of Sheffield, NorthernGeneral Hospital, Sheffield S5 7AU, UKAddress correspondence to G. K. Armstrong. Fax: (+44) I 14 271 5771; E-mail: g.k.armstrong@sheffield.ac.uk Abstract Objectives: to describe stability and change in levels of customary physical activity assessed in recall-basedquestionnaire surveys of older people conducted in 1985, 1989 and 1993- Design: longitudinal study. Subjects: 1042 people srcinally aged 65 and over randomly sampled from general practitioner lists in Nottingham,UK. Methods: logistic and multiple regression analyses, intraclass correlation coefficients. Main outcome measures: self-reported time spent per day walking and shopping; self-reported time spent perweek in other indoor, outdoor and leisure activities; frequency of performance of strength and  flexibility  activities. Results: among survivors, activity levels at baseline tended to be higher than those of their non-surviving peers.Overall, 8-year change between 1985 and 1993 was characterized by progressively declining activity levels.Nevertheless, in both trajectories and stability profiles, differences did emerge among the seven activity categoriesstudied. At least one in four respondents increased the time they spent walking, and approximately one in threerespondents increased the time they spent shopping between 1985 and 1993. Conclusions: these  findings  suggest that, while some activity variables show levels of stability consistent with trait-like constructs, others are clearly more labile. While the present data cannot offer a definitive explanation for thesedifferences, it seems reasonable that within each activity the influence of ability, opportunity and need interact todetermine levels of participation. Keywords: activity, ageing, exercise, leisure, longitudinal study, shopping, stability Introduction The physiological benefits of regular exercise andaerobic training have now been demonstrated acrossthe human Iifespan [1]. However, since current cohortsof elderly people show relatively low participationrates in sports and formal exercise programmes [2], thehealth implications of habitual or customary physicalactivity levels in later life have attracted particularattention [3 - 5]. While recall-based survey assessmentsof physical activity appear to offer a practical researchtool for both cross-sectional and longitudinal researchin this area, data on the reliability and stability of suchmeasurements remain scarce [6]. Nevertheless, theresearch literature continues to reflect the widespreadassumption that later life activity levels are trait-like (i.e.personally enduring) constructs the measurement ofwhich allows individual's to be classified on an active-inactive continuum (e.g. [7]). For a variety of reasons,activity levels can be expected to decline withadvancing age. However, the extent to which olderindividuals might maintain their relative position onsuch a continuum remains unknown.Using 8-year data from the Nottingham LongitudinalStudy of Activity and Ageing (NLSAA) [8], this paperexplores these assumptions by examining temporaltrends in physical activity levels among survivors of arandom sample, all of whom were aged 65+ at baseline.Specifically, the analyses focus on aspects of stabilityand change with the aim of (i) describing stability/change in the overall levels of activity participationamong survivors of the srcinal sample and (ii)estimating stability/change in the relative position ofrespondents within selected distributions of activityvalues. Methods Data were derived from the NLSAA, full details of which 17   b  y g u e  s  t   on N o v e m b  e r 2  0  ,2  0 1 1 h  t   t   p :  /   /   a  g e i  n g . oxf   or  d  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   G. K. Armstrong, K. Morgan are presented elsewhere [8]. Briefly, the NLSAA is an 8-year survey of activity, health and wellbeing conductedwithin a representative stratified sample of peoplesrcinally aged 65 and over. The baseline (Tl) surveyfor the NLSAA was conducted between May andSeptember 1985, during which time 1042 people(507 aged 65-74; 535 aged 75+), randomly sampledfrom general practitioner's lists, were interviewed intheir own homes (a response rate of 80%). Subsequentanalyses showed that the age, sex, and social classstructure of this sample closely resembled that forEngland and Wales as a whole. Follow-up surveys wereconducted at 4-yearly intervals in 1989 (T2) and 1993(T3), with re-interview rates of 88% (690 interviewsfrom 781 eligible respondents) and 73% (410 inter-views from 564 eligible respondents) respectivelyobtained among survivors [8]. Assessment of customary physical activity (CPA) For the questionnaire assessment of CPA, all activitieswere divided into seven mutually exclusive functionalcategories: outdoor productive activities (e.g. garden-ing, house and car maintenance), indoor productiveactivities (e.g. housework, decorating, indoor main-tenance), walking (purposeful walking outside thehouse or garden), shopping (i.e. continuous ambula-tory behaviour associated with shopping), leisureactivities (e.g. cycling, swimming), strength activities(e.g. climbing high steps, dragging heavy loads) andjoint flexibility activities (e.g. reaching for high shelves,bending for low shelves). Time spent walking andshopping was scored as min per typical day [9]. Timespent in all other continuous activities was scored asmin per week. For strength and flexibility activities, atotal score was calculated from individual tasks, eachscoring 0-4 for the following ordered categoricalresponse: performed never; performed occasionally;performed once or twice a week; performed daily;performed several times a day. Statistical analysis To summarize the data, and allow for comparisons ofresults from all three survey waves, data for indoor,outdoor, leisure, walking and shopping activities wererecoded into appropriate time categories. Multipleregression, adjusting for age, was used to estimate themean differences for men and women in baseline (Tl)levels of indoor activities and strength and flexibilityscores. The indoor activity variable was square roottransformed before the regression analysis. Since aproportion of older people recorded 0 scores onoutdoor, leisure, walking or shopping activities, binaryvariables (none versus some) were created and used inthe logistic regressions to estimate the differencesbetween men and women, again adjusting for age. Forthe multiple and logistic regression analyses, age inyears and a dummy variable for gender with male = 0and female = 1 were entered into the model. Multipleand logistic regressions were also used to assessdifferences in Tl CPA levels between those who did,and those who did not survive to 1993. Age in years,gender, and the dummy variable died = 0 and alive in1993 = l were entered into these models. All data wereanalysed using SPSS for Windows (Release 6.0) [10]. Analyses of survivors Respondents who were still alive in 1993 and with dataat all three time points were classified as an elite sub-group, and used to assess stability and change in CPAlevels. To assess the temporal stability of an individual'sposition within each activity distribution (i.e. to assessthe extent to which individuals remain more, or lessactive than their peers), activity values were standard-ized (z-scores) for each survey wave. Intraclasscorrelation coefficients QCC) were then calculatedfor each activity using the 2r-score transformed values,providing an estimate of the average correlation amongmeasurements. A one-way analysis of variance wasfitted to the z-scores and the ICC (p) was calculated as: P = ° subject^subject ' ^ error Results Indoor, outdoor and leisure activities Levels of indoor, outdoor and leisure activities areshown in Table 1. The table is split by age group in1985 and by gender. All 1985' are the distributions forthe total baseline sample interviewed at Tl in 1985.The distributions of the elite sub-group of older peopleat all three time points are also shown. Gender differences Significant differences were present in the levels ofindoor, outdoor and leisure activities between men andwomen in 1985. A higher proportion of women didmore indoor activities per week than men (square roottransformed: adjusted j3 = 8.77; 95% CI 7.55-10.00,P< 0.001). The reverse was true for outdoor andleisure activities. A higher proportion of women did nooutdoor activities compared with men [adjusted oddsratio (OR) = 0.39; 95% CI 0.30-0.51, P<0.001[.Women were also less likely to participate in leisureactivities (adjusted OR = 0.61; 95% CI 0.47-0.79,< 0.001). Stability and change Older people who were still alive in 1993 did more 18   b  y g u e  s  t   on N o v e m b  e r 2  0  ,2  0 1 1 h  t   t   p :  /   /   a  g e i  n g . oxf   or  d  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   Stability and change in levels of physical activity in later life Table I. Time spent per week in indoor, outdoor and leisure activities by all subjects and by the elite sub-group a Activity/age group/time spent (h/week) Indoor 65-74 years in 1985 0 ^3 >3-7>7-l4 >14 n 75+ years in 1985 0=£3 >3-7 >7-l4 >14 n Outdoor 65-74 years in 1985 0 ^3 >3-7 >7 n 75+ years in 1985 0 ^3 >3-7 >7 n Leisure 65-74 years in 1985 0=£3 >3-7 >7 n 75+ years in 1985 0 ^3 >3-7 >7 n % of subjects MenAll 1985 24%27%29%15% 5% 216 29%25%24%17% 4% 181 25%20%18% 37% 218 47% 20% 11% 22% 181 41% 24%17%18% 217 51%21% 12% 16% 181 Elite1985 20%30%26%16% 7% 99 19%19% 35% 19% 6% 31 10%20% 21% 48% 99 26%26% 29%19% 31 35% 22%20% 23% 100 39% 19% 23% 19% 31 1989 25%26% 23% 17% 8% 99 23% 39% 26%10% 3% 31 16%15% 31% 37% 99 39% 26%16%19% 31 49% 19%18%14% 100 58%19% 6% 16% 31 1993 27%32%29% 8% 3% 99 29% 35% 26%10% 0%31 30% 33% 10% 26% 99 61% 16% 6% 16% 31 62% 23% 10% 5% 100 55% 32%10% 3% 31 Women All 1985 4% 7% 31% 36% 22% 283 9% 17%29%28%17% 336 46% 29%15%10% 283 71% 18% 8% 4% 336 55% 27%12% 6% 283 63% 27% 8% 2% 336 Elite1985 0%7% 32% 37%24% 153 3% 13% 31% 28%25% 96 37% 31% 20% 13% 143 54% 22%14%10% 79 47% 31% 15% 8% 144 48% 34% 14% 5% 80 1989 4% 7% 30%37%22% 153 2%20%40%28%10% 96 48%28% 11% 13% 143 63% 19%10% 8%79 53% 28%10% 8%144 69% 20%10% 1%80 1993 5% 17% 44% 27% 7%153 23% 20% 31% 24%2% 96 58% 27%10% 6% 143 78%16% 1% 4% 79 74%19% 6% 1% 144 86% 9% 3%3% 80 Older people who are still alive in 1993, for whom data are available for all three time points. 19   b  y g u e  s  t   on N o v e m b  e r 2  0  ,2  0 1 1 h  t   t   p :  /   /   a  g e i  n g . oxf   or  d  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   G. K. Armstrong, K. Morgan Table 2. Changes between the categories (scores for strength and flexibility) of habitual physical activity over the 8-yearperiod 1985-93 ActivityIndoorOutdoorLeisureWalkingShoppingStrengthFlexibility Men % showingDecrease 38% 51% 49% 41% 27%40% 59% change in None 41% 43% 41% 34%39% 8% 9%categoryIncrease 22% 6% 11% 25% 34% 52%32% n 130130131120120131132 Women% showingDecrease 58% 41% 44% 36% 29% 61% 67% change in None 29%50%47% 36%39% 8% 11% categoryIncrease 13% 10% 9% 28%32% 31% 22% n 249222224 196 192252 254indoor activities in 1985 than those who died withinthe 8 year period (square root transformed: adjusted (3 = 2.11; 95% CI 0.83-3.38, P<0.001). Table 1 showsthat the distribution of time spent on indoor activitiesby the elite sub-group of older people reduced overtime in each age/gender group. At the individual level,more than 50% of women had reduced their time spenton indoor activities over the 8-year period, whilst therewas no change for 41% of men (Table 2). Table 2 alsoshows that a further 22% of men had increased theirtime spent on indoor activities over the same period.The stability of an individuals position relative to others, as indicated by intraclass correlation coeffi-cients (average correlation among two measurementson the same person) computed for z-score transformedvalues, for indoor activities was fair for both men and women (Table 3). Survivors in 1993 were more than twice as likely in 1985 to have spent time on outdoor activities than thosewho died before 1993 (adjusted OR =2.10; 95% CI 1.58-2.80, P< 0.001). Nevertheless, within the elitesub-group, the distribution of time spent on outdooractivities decreased over 8 years in each age/genderTable 3. The intraclass correlation coefficient 3 of the z scores for each habitual physicalactivity by genderCorrelation coefficientActivity Men WomenIndoorOutdoorLeisureWalkingShoppingStrengthFlexibility0.310.500.450.450.170.490.390.270.580.250.180.160.560.48 ã Average correlation among two scores on the samesubject. group (Table 1). Table 2 also shows that 43% of men and 50% of women spent the same time on outdooractivities in 1993 as they did in 1985. Intraclasscorrelations showed only moderate stability for outdooractivities (Table 3). Again, older people still alive in 1993 were morelikely in 1985 to have participated in leisure activitiesthan those who had died within the 8-year period(adjusted OR=1.63; 95% CI 1.24-2.15, /><0.001).Table 1 also shows, however, that for the elite sub- group, participation in leisure activities decreased overtime for each age/gender group. Overall, 49% of menand 44% of women reduced their participation in leisure activities from 1985 to 1993 (Table 2). The stability of an individual's position relative to others for leisure activities was lower for women (ICC = 0.25)than for men (ICC = 0.45; Table 3). Walking and shopping Gender differences In 1985, over 60% of older people in each age/gendergroup walked less than 30 min on a typical day (i.e. lessthan 3-5 h a week; Table 4). Women were less likely to walk on a typical day than men (adjusted OR = 0.65; 95% CI 0.49-0.86, P<0.01). Although a high propor-tion of older people did not shop in 1985, there wereno statistically significant differences between men and women (adjusted OR=1.27; 95% CI 0.95-1.71, Stability and change Older people who were alive 8 years later were no more likely to have walked on a typical day in 1985 than those who died before 1993 (adjusted OR= 1.28; 95% CI 0.96- 1.71, P= 0.09). Table 4 shows that for theelite sub-group of older people, the distribution of timespent walking decreased over the 8 years, although 35% of women aged under 75 years did no walking per 20   b  y g u e  s  t   on N o v e m b  e r 2  0  ,2  0 1 1 h  t   t   p :  /   /   a  g e i  n g . oxf   or  d  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om 
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