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Physical activity and functional limitations in older adults: a systematic review related to Canada's… Paterson, Donald H; Warburton, Darren E May 11, 2010

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Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activ-ity 2010, 7:38Open AccessR E V I E WReviewPhysical activity and functional limitations in older adults: a systematic review related to Canada's Physical Activity GuidelinesDonald H Paterson*1,2 and Darren ER Warburton3,4AbstractBackground: The purpose was to conduct systematic reviews of the relationship between physical activity of healthy community-dwelling older (>65 years) adults and outcomes of functional limitations, disability, or loss of independence.Methods: Prospective cohort studies with an outcome related to functional independence or to cognitive function were searched, as well as exercise training interventions that reported a functional outcome. Electronic database search strategies were used to identify citations which were screened (title and abstract) for inclusion. Included articles were reviewed to complete standardized data extraction tables, and assess study quality. An established system of assessing the level and grade of evidence for recommendations was employed.Results: Sixty-six studies met inclusion criteria for the relationship between physical activity and functional independence, and 34 were included with a cognitive function outcome. Greater physical activity of an aerobic nature (categorized by a variety of methods) was associated with higher functional status (expressed by a host of outcome measures) in older age. For functional independence, moderate (and high) levels of physical activity appeared effective in conferring a reduced risk (odds ratio ~0.5) of functional limitations or disability. Limitation in higher level performance outcomes was reduced (odds ratio ~0.5) with vigorous (or high) activity with an apparent dose-response of moderate through to high activity. Exercise training interventions (including aerobic and resistance) of older adults showed improvement in physiological and functional measures, and suggestion of longer-term reduction in incidence of mobility disability. A relatively high level of physical activity was related to better cognitive function and reduced risk of developing dementia; however, there were mixed results of the effects of exercise interventions on cognitive function indices.Conclusions: There is a consistency of findings across studies and a range of outcome measures related to functional independence; regular aerobic activity and short-term exercise programmes confer a reduced risk of functional limitations and disability in older age. Although a precise characterization of a minimal or effective physical activity dose to maintain functional independence is difficult, it appears moderate to higher levels of activity are effective and there may be a threshold of at least moderate activity for significant outcomes.IntroductionThis review is focused on the relationship between physi-cal activity and functional outcomes for older adults (>65years of age, but <85 years of age) in the general "commu-nity-dwelling" population. A significant body of researchhas also examined the relationship between physicalactivity and outcomes of premature all-cause mortalityand morbidity (of various chronic diseases). This evi-dence has been detailed in the companion paper review-ing physical activity for "adults" [1] and has beenreviewed previously (see [2,3]). This research has demon-strated compelling support for the health benefits ofphysical activity across the adult lifespan.Previous studies of morbidity and mortality in adults* Correspondence: dpaterso@uwo.caBioMed Central© 2010 Paterson and Warburton; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and repro-duction in any medium, provided the original work is properly cited.have provided important information for "older" individ-1 School of Kinesiology, University of Western Ontario, London, Ontario, CanadaFull list of author information is available at the end of the articlePaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 2 of 22uals. In fact, studies with a group mean age of 45-50 yearsoften included participants who were at least 65 years ofage, and a follow-up period of 5 years or more (see [2]).The findings of these studies are weighted strongly by theoutcome incidence or prevalence being much greater inthe older groups, and thus the information is very appli-cable to the older population. Indeed some studies havefocused on older adults; and some have sub-divided theirpopulation by age facilitating interpretations for differentage groups. In gestalt overview these latter groups ofstudies suggest a somewhat lower requisite "intensity" ofexercise (even in relative terms) to delay mortality orreduce the incidence of disease for older adults comparedto middle-aged groups [2]. A number of these studieshave specifically examined walking and whether the"amount" of walking relates to outcomes. Indeed thesedata show that walking is a physical activity that leads todecreases in all-cause mortality and in morbidity. Theamount of walking is often equivalent to approximately1000 to 1500 kcal/week (4200 to 6300 kJ/week), butsometimes less (minimally 500 kcal/week; 2100 kJ/week);and the intensity within the walking domain may beimportant for health benefits (see [4]), but again, mini-mally, even normal walking speeds have been related tobetter outcomes. Further research is clearly warranted toevaluate the minimal requisite intensity of physical activ-ity or exercise for (morbidity and mortality) health bene-fits in the older adults.It is essential to highlight that many older individualsconsider the capacity to carry out activities of daily living(i.e., functional independence) to be of greater concernthan prevention of disease [5-7]. Moreover, the health-related quality of life and life expectancy of individualswho live in a dependent state is greatly reduced. Theassociated nursing home or long-term care health-carecosts of are high. Research (as reviewed in this paper) hasincreasingly examined the role that habitual physicalactivity plays in the maintenance of functional indepen-dence. However, questions remain regarding the minimal,and dose-response characteristics of the intensity andamount of physical activity or exercise required for themaintenance of functional independence in older adults.Accordingly, the present paper analyses the relationshipbetween physical activity and outcomes related to func-tional limitations, disability and loss of independence inolder adults. The primary purpose of this systematicreview is to examine the role of physical activity in themaintenance of functional independence in the elderly.Furthermore, it is our intention to focus on the functional(physical) and cognitive determinants of independence inhealthy (asymptomatic) individuals and derive a recom-The present "aging population" will result in substantialincrease in the numbers and proportion of older adults.Aging is characterized by loss of function and prevalenceof chronic diseases and older adults are among the mostsedentary (physically inactive) segment of society. Inmany respects the increased life expectancy now appearsto be exceeding our ability to maintain function and func-tional independence. A large proportion of older adultsmay live perilously close to important thresholds of phys-ically ability that may render them dependent. Thereduced quality of life and the social and economic(health-care) consequences are staggering. In terms ofpublic health the benefits that may be derived with amore physically active older population may be essentialin the maintenance of our health-care system.MethodsIn analysis of physical activity, specifically for olderadults, it was decided that an important aspect was main-tenance of functional abilities and functional indepen-dence (i.e., "performance-related fitness") with functionaloutcomes to supplement the information on "health-related fitness" of all-cause mortality and morbidity out-comes, reviewed in the adult paper by Warburton et al.[1] and by Paterson et al. [2]. Functional outcomesincluded assessments of functional status decline, impair-ment or functional limitations, or disability, includingself-report questionnaire assessments or measured physi-cal performance tests. Thus prospective cohort studies ofthe relationship between physical activity and functionaloutcomes were reviewed. Determining the nature of thephysical activity that was related to outcome measuresrequired close inspection of the criteria set out in eachstudy, as there was no consistent categorization of physi-cal activity groupings or of the components of physicalactivity that might relate to the dose-response. In somestudies the physical activity was quantified by volume (asa total energy expenditure, or as a frequency and durationof activities) and other studies also attempted to accountfor the relative intensity of the activities (light, moderate,vigorous) and types of activity (walking, exercising, sportsplay, recreation, household chores). Thus, the level ofphysical activity was determined from analysis of types ofactivities that were reported for each activity level in eachstudy; for example, in a number of studies there were onlytwo activity groups but to be in the higher group therehad to be report of vigorous activities (sports) or walkingof about 1 hour per day. This analysis was used to catego-rize the physical activities or physical activity groups thatwere related to the outcome as those of: vigorous activi-ties and/or high volume of systematic activity (walkingmended types of physical activity and volume and inten-sity dose-response relationships required to achieve thesehealth benefits.for exercise); moderately-vigorous groups as the activitiesincluded vigorous activity (not included in moderategroup) or walking for exercise, but at a lower volume thanPaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 3 of 22for the vigorous high-volume group; moderate levels ofactivity from participation in normal walking or garden-ing with a volume of 3-5 days/week and 30 min per day;participation mainly in light activities of daily living withonly occasional walking or gardening.Additionally it was recognized that as well as reviewingstudies of the relationship of physical activity with out-comes in the long-term, or the effects of life-long physicalactivity (as characterized in prospective cohort studieswith a relatively long-term follow-up), it was also essen-tial to analyse the short-term outcomes of the moreimmediate effects consequent to physical activity inter-ventions over a few weeks to months. Thus, the moreimmediate effects of exercise training programmes onphysiological outcomes related to increased cardiorespi-ratory fitness or strength aspects which were reviewed inPaterson et al. [2] were supplemented in this review withresults of short-term exercise interventions that reportedfunctional outcomes. Thus, aerobic and strength exercisetraining programmes with functional outcomes werereviewed.Criteria for considering studies for this reviewThe review was restricted to published, original, scientificjournal manuscripts written in English. Studies evaluat-ing the relationship between the "intervention" of anyphysical activity (or cardiorespiratory or strength assess-ment) and outcomes of variables related to functionalindependence and of cognitive function were included.Population samples included asymptomatic "community-dwelling" older adults between 65 and 85 years of age.The review was restricted to participants with "mini-mal" initial impairment or functional inability; thus, stud-ies of rehabilitation, subject groups initially very old (e.g.,> 85 years of age), those considered to be "frail", individu-als in nursing home environments, and those in long-term care were excluded. Studies of samples with specificdisease or conditions (e.g., diabetes, heart disease, priorstroke) were also excluded, with the exception of studiesincluding participants with arthritis as this conditionaffects a large portion of older adults.As a functional outcome, the extensive literatureregarding "falls" as a major outcome was not included,since a falls outcome differs from an outcome of disabilityor functional limitation, and studies have suggested thatfalls can be prevented through specific modification tothe physical activity prescription (i.e., by including bal-ance activities). Additionally, outcomes of anxiety anddepression are not reviewed as these are specific clinical(or sub-clinical) conditions and their treatment may allowmodification of the "general" physical activity "prescrip-existing dementia and/or Alzheimer's disease wereexcluded from the analyses.Search strategyLiterature searches were conducted in the following elec-tronic bibliographical databases:• MEDLINE (1966-March 2008, OVID Interface);• EMBASE (1980-March 2008, OVID Interface),• CINAHL (1982-March 2008, OVID Interface);• PsycINFO (1840-March 2008, Scholars Portal Inter-face);• Cochrane Library (-March 2008),• SPORTDiscus (-March 2008).The Medical Subject Headings (MeSH) were keptbroad. See Tables s1 and s2 (see additional file 1) forexamples of the complete MEDLINE search strategy andkeywords used. The electronic search strategies were cre-ated and carried out by researchers experienced with sys-tematic reviews of the literature. Searches were limited tothe English language, human subjects, and participantsover age 65 years. The citations and applicable electronicversions of the article (where available) were downloadedto an online research management system (RefWorks,Bethesda, Maryland, USA). Duplicate citations wereremoved.ScreeningTwo reviewers (research staff ) independently screenedthe title and abstract of the citations to identify potentialarticles for inclusion. The reviewers were not blinded tothe authors or journals. For those articles that appearedrelevant, the full text study report was obtained and datawas extracted using a common template. Selected articleswere retrieved electronically or manually via the Cana-dian interlibrary system. Disagreements regarding inclu-sion were resolved through discussion with a thirdreviewer. All studies that were excluded during the cita-tion and full-article screening processes were recorded(this list of excluded studies is available upon request).Reference lists of key studies and reviews in the field werealso cross-referenced in order to identify further litera-ture and references from personal files were added. (It isnoted that this cross-referencing yielded many studiesnot found in the electronic search, particularly for pro-spective cohort studies of the relationship between physi-cal activity and functional outcomes. The search strategyproblems appear to relate mainly to two factors: the studysample ages were often given for the study baseline (as <65 years) but with the follow-up time the data actuallymet the inclusion age (>65 years) (and these referencesbecame included from the cross-reference or personaltion" to achieve an outcome related to the specific clinicalcondition. Similarly, studies examining persons with pre-files search); the terms related to functional outcomes arenot standardized and often the functional outcomes werenot in the title or abstract.)Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 4 of 22Data ExtractionTwo reviewers (research staff ) completed standardizeddata extraction forms. One person performed the dataextraction for each paper assigned to them and theextraction was verified by another reviewer. Informationwas extracted regarding the study design, the countrywhere the study was conducted, the participant charac-teristics, the sample size, the objectives of the study, themethodologies employed, the major outcomes of func-tional decline or limitation, disability or dependence, andthe results and conclusions of the studies. The reviewerswere not blinded to the journal or the author names whenextracting information from the articles. Subsequently,one author (and one research staff ) extracted furtherdetail or clarifications as needed in assembling theTables, and completed the tabular data for referencesobtained from cross-referencing subsequent to the elec-tronic search.Level of EvidenceThe approach used to establish the level and grade of evi-dence was consistent with that used during creation ofthe "Canadian clinical practice guidelines on the manage-ment and prevention of obesity in adults and children"[8]. The level of evidence provides information regardingthe strength of the evidence in favour of physical activity/exercise in the primary prevention of functional limita-tions, disability or dependence. This evaluation process isbased on a pre-defined and objective criteria (see Table s3in additional file 1). Thus, grade and level of evidencewere assessed for both general recommendations regard-ing physical activity for older adults, and also for morespecific guidelines regarding the appropriate dose ofphysical activity and the strength of the data supportingthe recommendation. A physical activity guideline thatreceives the highest grading would indicate that the bene-fits clearly outweigh the risk and receive a strong support.However in the present review "risks" of physical activitywere not assessed. Studies reviewed in this paper did notreport or assess risks such as acute cardiovascular eventsassociated with increased physical activity (see AmericanHeart Association Scientific Statement by Thompson etal. [9]). The studies reviewed also did not report on theincidence of injury in more physically active individuals,or with increases in physical activity.Quality AssessmentThe Downs and Black [10] scale was selected to assess thequality of each study as it is appropriate to evaluate non-randomised investigations, and it contained the highestnumber of relevant items for the needs of this review.(randomised control trials), and non-RCT study types.Thus, the quality of each study was also established simi-lar to the method of Gorber et al. [11] to include the mostrelevant components of the scoring tool. Therefore, amodified version of the Downs and Black checklist wasused with the final checklist consisting of 12 items with amaximum score of 12 points for the studies of a prospec-tive cohort design (with functional outcomes or cognitiveoutcomes). For studies of exercise training interventionsthe scale was modified to 22 items or an additional oneitem for the RCT exercise training interventions and totalscore of 23 or 24, respectively. Higher scores reflected asuperior quality of investigation.Integration of FindingsDue to the heterogeneity across study populations, meth-ods used, and outcomes assessed in drawing conclusionsand recommendations from the review we conducted anarrative synthesis of the results.ResultsFunctional IndependenceSearch Results: Physical Activity and Functional IndependenceA total of 2,309 citations were identified during the elec-tronic database search (Figure 1). Of these citations,1,209 were identified in MEDLINE, 780 in EMBASE, 123in Cochrane, and 197 in the CINAHL/SportDiscus/PsychInfo search. A total of 229 duplicates were found,leaving a total of 2,080 unique citations. A total of 1,735articles were excluded after scanning, leaving a total of345 articles. From these articles 260 were excluded afterfurther (abstract) review leaving 85 articles. The reasonsfor exclusion included: participant group did not meetthe inclusion criteria for age, absence of disease (i.e.,study was of a clinical population) or for life-style (werenursing home or long-term care residents or of a "frail"sample or >85 years of age versus community-dwellingolder adults); functional measure not reported; physicalactivity level or exercise capacity not reported; or thecitation was a review, dissertation, thesis, or abstract.With full review 24 further papers did not meet inclusioncriteria, leaving 61 articles. A further 19 (now n = 42)were omitted as the subject sample was actually a frail,not community-living group (n = 15), with others omit-ted when detailed reading showed no acceptable func-tional outcome measure (these had included falls oranxiety and depression outcomes). Lastly (as explainedlater) it was decided not to include studies of cross-sec-tional design regarding the relationships between physi-cal activity and functional outcome, and this eliminated aHowever, as not all items were relevant to the variousstudy types included in this review, a modified version ofthe checklist was employed for each of prospective, RCTfurther 12 studies. Thus the search revealed 30 studiesfully reviewed for inclusion in the systematic review andsummarized on the extraction Tables. Additional litera-Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 5 of 22ture was tracked from reference citations and author files.These searches provided an additional 36 studies (and 11supplementary reports). Therefore, a total of 66 uniquestudies were included in the systematic review of the lit-erature regarding the relationship between physical activ-ity and functional independence.Data from longitudinal or prospective studies with anoutcome of functional limitation were considered mostinfluential in our analyses. Cross-sectional or retrospec-antedated the functional decline or were a consequenceof the functional decline. Thus, for cross-sectional or ret-rospective analyses of the relationships between physicalactivity and functional outcomes we have not performedan exhaustive systematic review but have cited somestudies that were influential in the field. Exercise trainingstudies that included an outcome of function were alsoexamined. These included exercise training interventionsof either aerobic or aerobic supplemented with resistancetraining, or programmes of resistance training alone.These studies allow for the examination of the moreimmediate effects of increased physical activity, but usu-ally only assessed proxy measures of function that mightbe related to subsequent limitations or disability,whereas, the longitudinal studies generally indicated therelationships of physical activity status with function overa more prolonged period of time.Prospective cohort studies of physical activity and functional limitations in older adultsDescription of Studies (population, intervention, outcome) The present review captured articles analysingassociations between physical activity or cardiorespira-tory fitness or muscle (strength) fitness with outcomes ofimpairment or functional limitation (or functional statusdecline) or disability in older adults using a longitudinal,prospective cohort design. Table s4 (see additional file 2)provides summary details of 35 prospective cohort stud-ies (plus 7 "supplemental" reports from the same database with different outcome measures or with a longerfollow-up). Table s4 (see additional file 2) captures studiesfrom 1995 to 2008; earlier studies have been frequentlyreviewed (see [12,13]). The 35 studies included 83,740participants with study sizes ranging from 141 to 10,209participants. About half of the studies (n = 19) were oflarger sample sizes with subject numbers from ~1000 to10,000 (median 3075) with most of the remaining studieswith sample sizes usually of 200 to 400 (but with up to800 subjects, median = 387). Ethnicity was generally notreported explicitly, although two studies reported onAfrican Americans ("Blacks") and Caucasians ("Whites"),one was of Japanese Americans and one of MexicanAmericans. Data were obtained from studies from a vari-ety of countries and regions including the USA (21), Fin-land (3), Denmark (2), UK (2), Canada (1), Taiwan (1),Israel (1), and a combination of countries (Finland, Italyand the Netherlands, n = 2; Europe, n = 1; and USA withEngland, n = 1).Age groups studied included samples: of "younger" age,starting the study in their 6th decade with follow-up gen-erally at a mean age of 65 to 70 years (11 studies); "older"groups initially aged 60 to 70 years and followed-up inFigure 1 Results of the literature search for functional limitations.Citations from electronic database search: MEDLINE   1209 EMBASE     780 Cochrane     123 CINAHL/SportDiscus/PsycInfo   197  Total Citations Downloaded to RefWorks: Total in RefWorks  2309 Total with Duplicates Excluded (N = 2080Articles Excluded after Full Review  N =43 And Cross-sectional studies (N = 12) Articles Included (N = 30) Articles Included from Search of Biographies and Authors Knowledge of Area (N = 36) Total Articles Included (N = 66) Full Articles Assessed for Eligibility after Scanning (N = 85) Citations Excluded after Scanning Titles/Abstracts (N = 1995) tive studies were considered; however, these studies wereoften limited as they did not adequately discriminatewhether the factors associated with functional limitationstheir mid-seventies (13 studies); and, "oldest" groups aged70 years and up with many followed into their late-seven-ties and older (5 studies); and the other studies surveyed aPaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 6 of 22very broad age range. Most studies included both menand women, but a few were of men only (n = 7) or womenonly (n = 1).The "intervention" of interest was physical activity.Physical activity reports were almost all from self-reportquestionnaires (with one study also having an objectiveassessment of physical activity, and two studies also mea-suring cardiorespiratory fitness). About one-half of thestudies used "walking as exercise" and various other activ-ities described as "vigorous" as those "counting" towardbeing physically active (mostly in samples of youngerbaseline age). Thus, it was possible from studies to char-acterize the variety of aerobic activities as being of light,moderate or vigorous intensity. About one-third of thestudies used some assessment of total score for a breadthof activities, with a few focused mainly on assessing fre-quency and distance of walking as the main activity (usu-ally in older groups), but in general a distinction betweenfrequency and duration was not clear and thus only total"volume" of activity could be characterized. In six [14-19]reports the "exercise group" were members of a joggingclub (over the long-term) or long-term adherents to exer-cise programmes, compared with a reference group. Ingeneral physical activity level was categorized into groupswith the studies using two groups (n = 9) or three groups(often tertiles, n = 9) or more groups or a continuousvariable (n = 8). In a small group of studies physical activ-ity assessment was made on more than one occasion, thusallowing groups to be formed to assess change in activitylevel (e.g. became active, or became inactive, or alwaysactive or inactive) over time [14,20,21]. For three studiesthe report was on the association of strength with func-tional outcomes [22-24].Outcomes of impairment or functional limitations, orfunctional status decline, or disability were all considered.Across the studies a very wide range of measures (fromdisability to self-report difficulties in tasks like walking400 m or taking a flight of stairs, and to performance testsinvolving walking speed, chair rises or carrying a load)were used to assess these functional independence out-comes. The outcome measures were mostly by self-reportquestionnaires. About one-half (n = 19) of the studiesused functional status questionnaires of abilities (or levelof difficulty) in activities of daily living (ADLs) andinstrumental ADLs (i.e. IADL) or the Health AssessmentQuestionnaire for Disabilities (HAQ-D1). Other categori-zations of similar low level functional capacity or depen-dence included self-report of functional status and"quality of life" questionnaires (including the MedicalOutcomes "Short-form 36" scale, SF36). In a few studiesthe report of a mobility limitation was also used as theassessed physical performances such as ability in stairclimbing or walking a distance, or tasks involving boththe upper and lower extremity (e.g., Huang et al.[25]), andfive studies reported on both ADL-type measures as wellas higher level performances. Only a very few studiesused a measured physical performance (a physical perfor-mance test battery, and/or short distance gait speed)."Performance" measures used as the outcome includedwalking speed or chair rises, with a common proxy ofmobility disability relating to various tests of walkingsuch as the 400 m walk.The period of follow-up ranged from 2 years up to 35years with many in the 5 to 10 year range (median follow-up 7 years), and included one-time follow-up (n = 22), butalso follow-up at multiple time points (two to four timepoints, or in some cases annual evaluations), (n = 13). Inanalyses of the relationship of physical activity and func-tional outcomes in all papers there were statistical adjust-ments for confounding variables.Results, Data Greater physical activity (categorized byvarious methods) predicted higher functional status(expressed in a variety of ways) in older age. To facilitateanalysis of these studies they have been grouped intothose with an outcome related to disability, and thosewith an outcome related to a higher level of functionssuch as functional limitation.In overview, with regard to an outcome of "disability" inADLs or IADLs, or a level of disability, studies have con-sistently shown a reduced risk in the more physicallyactive. A meta-analysis of the data was considered, how-ever, heterogeneity in both the categorization of physicalactivity levels and in the functional outcome measuresprecluded pooling the study results. Rather, Figure 2depicts that with higher levels of physical activity there isa reduction in risk for various outcomes related to func-tional limitations or disability with an "average" odds ratio(OR) of ~0.5. There is also the suggestion that a "moder-ate" physical activity level is also effective in preventingfunctional limitations and disability. Although two stud-ies [26,27] showed a significant trend across activity lev-els only one study [27] suggested a significant effect for alight or low physical activity group. Thus, it appears thatmoderate to high levels of physical activity are effective,but based on current literature there is limited justifica-tion for recommending the pursuit of merely a low levelof physical activity. Many of the studies emphasized intheir physical activity assessment the amount of walking,but wherein the duration or total walking (or the relativeintensity) to qualify in the higher versus lower activitygroups most often implied an "intention to exercise" ver-sus accumulating daily activities of various sorts. Thus,outcome. Eleven of the studies reviewed used functionallimitations or reported performance abilities at a muchhigher level usually in the younger samples. Thesealthough from the present data and in particular the vari-ety of ways in which physical activity was categorized, aspecification of a minimal amount (or intensity) of physi-Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 7 of 22cal activity needed for a reduction in risk of functionaloutcomes is not feasible, Figure 2 does suggest a 50%reduction in risk of functional limitation/disability is pos-sible with physical activity categorized as moderate tohigher levels in total amount and at least of moderate sus-tained intensity.It is instructive to examine some of the individual stud-ies to determine the physical activity categorizations thatresulted in reduced risk of functional disability. Chris-tensen et al. [28] reported being active versus sedentaryat age 70 years had an OR for disability at age 75 years of0.17. Haveman-Nies et al. [29] found for the intermediateand high-active versus low-active the risk of functionaldependence in ADLs was 0.53 in men and 0.38 in women.Schroll et al. [30] summarized studies in a Danish popula-tion; in older age the OR for mobility dependence waslevels of impairment and functional decline. In Wu et al.[32] those who participated in "routine exercise" had anOR of 0.52 for subsequent ADL disability.From five studies (see Figure 2) it is possible to analysedose-response relationships between different physicalactivity levels and a disability outcome. Boyle et al. [33]noted a 7% reduction in disability risk for each hour ofwalking (and/or other exercise), or expressed another waya 40-50% reduction in risk with 1 hour of such activitiesdaily (7 to 8 hours per week). Leveille et al. [26], for theprobability of disability versus being free from ADL dis-ability prior to death, expressed a 0.53 odds ratio in thoseof higher levels of physical activity, but not for intermedi-ate activity levels, versus the low activity group; neverthe-less, the statistical trend across categories of physicalactivity was significant. Østbye et al. [27] reported the ORFigure 2 Prospective cohort studies of the odds ratio of functional limitations or disability in ADLs and IADLs or quality of life disability in-dexes in relation to physical activity level. The odds ratio (OR) for each level (1,2,3) of physical activity are compared with the lowest physical activity group assigned as the referent (physical activity group = 0, OR = 1). The odds ratios are those reported for analyses statistically adjusted for confounder variables. The OR is an approximation as the actual data may have been separated into men versus women, or other groupings and thus in assembling the data these values have been combined. The level of physical activity was determined from analysis of types of activities that were reported for each activity level in each study; for example, in a number of studies there were only two activity groups but to be in the higher group there had to be report of vigorous activities or walking of 1 hour per day. Thus the physical activity groups were determined to require: 3 - vigorous activities and/or high volume of systematic activity (walking for exercise); 2 - moderate level of activity from participation in normal walking or gardening with a volume of 3-5 days/week and 30 min per day; 1 - participation mainly in light activities of daily living with only occasional walking or gardening; and some physical activity groups were scored as 2.5 as they included vigorous activity (not included in group 2) or exercise walking but at a lower volume than group 3. Dashed lines indicate study data where only two activity groups were categorized, whereas solid lines join the data points for studies in which more than two activity groups were formed.Physical Activity Level0 1 2 3Odds Ratio0.00.20.40.60.81.0Boyle [33] Christensen [28]Haveman-Nies [29]Leveille [26]Ostbye [27]Paterson [5]Schroll [30]Van Den Brink [34]Wu [32]~0.25 in physically active (approximately 20 min/day or2-3 hours/week) versus sedentary. Unger et al. [31]showed greater frequency of walking was related to lowerfor ADL disability or dependence was more linearlyrelated to activity level from light with OR ~0.5, throughmoderate with OR ~0.4, to vigorous OR of ~0.2, with thePaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 8 of 22statistical test of trend across physical activity groupsagain significant. From Van Den Brink et al. [34] totalphysical activity in walking cycling and gardeningreduced risk of disability with OR in the range of 0.6 forthe middle-tertile and 0.4 for the highest-tertile com-pared to lowest, with duration of these activities (up to100 min per day) being the important criteria. Paterson etal. [5] reported the OR for those living independentlybecoming dependent in follow-up in relation to their car-diorespiratory fitness and demonstrated a ~30% reduc-tion in those of moderate and ~50% reduction in those ofhigher fitness versus the low fit group; however in thisstudy the reported physical activity levels among theolder groups were not related to subsequent dependence.There were two studies that had negative findings interms of supporting the relationship of greater physicalactivity with functional limitations or disability. Hirven-salo et al. [35] noted that for those with intact mobilitythe risk of dependency did not differ between active andsedentary. Wannamethee et al. [21] found that the inverserelationship between physical activity and mobility limi-tation showed a trend, but was not significant, when theodds ratio of moderately vigorous activity related tomobility limitation was adjusted for the presence ofchronic disease.In study samples at the "higher" function level the rela-tive risk or odds of functional decline or limitation wassignificantly reduced in those more physically active, usu-ally defined by regular, vigorous activities. Again a meta-analysis was not possible due to heterogeneity in thephysical activity categorizations and in the outcome mea-sures. Nevertheless, Figure 3 depicts in these studies therisk of a functional limitation outcome was again ~50%reduced in the high active group, and also a reduced oddsratio was evident in the moderately physically activegroup. Although a few studies (see below) showed a dose-response relationship only two studies actually had a lightphysical activity group to compare to a sedentary groupand thus to date there is not enough data or consistencyto support a recommendation of light activity. Thus, inoverview in preventing decline or limitations in "higher"levels of performance the comparisons have oftenrevealed that the physical activity is "exercise", or "vigor-ous", but there is some evidence for "moderate" activity aswell (e.g., a "middle" moderate-activity group versus sed-entary group).Again it is instructive to attempt to discern the levels ofphysical activity that were protective. The studies of Dun-lop et al. [36], Ebrahim et al. [37] (and follow-up report byWannamethee et al. [21], Haight et al. [38] and Lang et al.[39] each reported that "vigorous" exercise (3 times/weekodds ratios consistently close to 0.5. Huang et al. [25] alsoassessed higher level physical functions and reported anOR for prevalence of functional limitation of ~0.4 forthose of moderate and high fitness versus lower fitness,and an OR of ~0.7 for moderate and high versus lowphysical activity. Koster et al. [40] reported the protectiveeffect of physical activity (particularly for the high versuslow activity groups) on incident mobility limitationacross different adiposity levels and in overview the ORwas ~0.6. Stessman et al. [41] found an OR of 0.2 to 0.4for continued "ease" of performance of ADLs and IADLsin the group "exercising" at least 4 times/week. Straw-bridge et al. [42] reported an OR of 0.57 for variousdescriptors of loss of function in those who reported"often walking for exercise" versus those who did notreport walking for exercise. Wang et al. [43] included per-formance-based physical function measures and notedthat those who exercised 3 times/week or more had bet-ter functional outcomes and decreased rates of functionaldecline. Young et al. [44] found those who were high ver-sus low active on total activity level maintained optimalfunction for basic ADL with an OR of 0.43, and for physi-cal endurance type tasks an OR of 0.59 versus the lowactive subjects (and in those with a chronic disease atleast moderate physical activity appeared sufficient tomaintain physical functioning).The study of Wannamethee et al. [21] is of importanceas it examined the effect of change in physical activitylevel in older age. Wannamethee et al. [21] noted in themoderately vigorous physically active group the OR of amobility limitation was 0.77, compared to no vigorousactivity, and maintaining or taking up physical activitywas associated with less mobility limitation such thatbecoming active yielded an OR of 0.43 for mobility limi-tation versus remaining inactive.Seven of the studies shed light on the dose-responserelationship (with odds ratios available from 5 of thesestudies and plotted on Figure 3). Brach et al. [20,45] notedthat being consistently active (defined as 30 min/daymoderate physical activity, on most days, 1000 kcal/week;4200 kJ/week) was associated with better physical func-tion. Clark et al. [46] found that walking 4 to 7 days/weekreduced the onset of disability by 50 to 80% (OR 0.5 to0.2). In both Brach et al. [20] and Clark et al. [46] therewere trends across lower levels of physical activity (e.g.,walking 1 mile 2 times/week) or with some of the func-tional outcomes. Ferrucci et al. [47] expressed results ofan increased active life expectancy of about 4 years with a1 to 2 year compression of morbidity in the more activecompared to the lower quartile of activity, with incre-mental benefits in the moderate (2 quartiles) to upperof greater than 30 min) or as one stated "exercise at highaerobic levels" limited functional decline and functionallimitation in "high level" physical functioning tasks with(top quartile) activity groupings. Ebrahim et al. [37]reported an OR for locomotor disability of 0.7 in theoccasional or light active and 0.4 in the moderate to mod-Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 9 of 22erately-vigorous group, compared to the sedentary group,although from these data Wannamethee et al. [21]reported the trend (after adjustment for chronic disease)was marginally non-significant. Huang et al. [25]reported significant linear trends across both activity andfitness categories. From Visser et al. [48] in those meeting30 min of moderate activity on most days the hazard ratio(HR) of mobility functioning was ~0.5 versus the inactive,and in those who were "life-style active" but did not meetthe "exercise group criteria" the risk compared to theinactive was intermediate at ~0.7; also noted was theimportance of walking and expending 400 kcal/week(1680 kJ/week) in walking versus the inactive whichyielded a HR of ~0.6.The longitudinal data also include six studies [14-19]wherein analyses are done for older adults who werecommitted "joggers" or long-term exercisers. In theselife. However, it does not seem feasible to extrapolatethese findings in an exceptionally active group to deter-mine useful interventions for the general older popula-tion.Three studies related hand grip strength to subsequentdisability. With greater hand grip strength there was adecrease in functional limitations and disability in ADLs[22-24]. These studies show a relationship with strengthbut do not provide the evidence that regular, strength-related activities are associated with reduced risk of func-tional limitations. Buchman et al. [49] reported that bothphysical activity and leg strength were independent pre-dictors of mobility decline in older persons (age 80 years).Schroll et al. [30] reported that an increase in leg musclestrength over a 5-year period in women aged 75 years wasrelated to mortality (but not to functional outcomes) andthe strength factor was not significant for men. Neverthe-Figure 3 Prospective cohort studies of odds ratio of lower functional performance or functional limitations in "higher" level functions (such as walking a distance or climbing stairs) in relation to physical activity level. The odds ratio (OR) for each level (1,2,3) of physical activity are com-pared with the lowest physical activity group assigned as the referent (physical activity group = 0, OR = 1). The odds ratios are those reported for anal-yses statistically adjusted for confounder variables. The OR is an approximation as the actual data may have been separated into men versus women, or other groupings and thus in assembling the data these values have been combined. The level of physical activity was determined from analysis of types of activities that were reported for each activity level in each study; for example, in a number of studies there were only two activity groups but to be in the higher group there had to be report of vigorous activities or walking of 1 hour per day. Thus the physical activity groups were determined to require: 3 - vigorous activities and/or high volume of systematic activity (walking for exercise); 2 - moderate level of activity from participation in normal walking or gardening with a volume of 3-5 days/week and 30 min per day; 1 - participation mainly in light activities of daily living with only occasional walking or gardening; and some physical activity groups were scored as 2.5 as they included vigorous activity (not included in group 2) or exercise walking but at a lower volume than group 3. Dashed lines indicate study data where only two activity groups were categorized, whereas solid lines join the data points for studies in which more than two activity groups were formed.Physical Activity Level0 1 2 3Odds Ratio0.00.20.40.60.81.0Clark (Blacks) [46]Clark (Whites) [46]Dunlop [36]Ebrahim [37]Haight [38]Huang (fitness) [25]Huang (pa) [25]Koster [40]Lang [39]Stessman [41]Strawbridge [42]Visser [48]Wannamethee [21]Wannamethee (change) [21]Young [44]studies the jogging groups or those exercising at high lev-els in middle-age and later clearly postponed a disabilityor functional limitations and prolonged disability-freeless a dose- response relationship was reported fordeclining muscle mass in relation to functional limita-tions in both men and women.Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 10 of 22Interpretation Overall it can be concluded from pro-spective studies that regular physical activity (in "aerobic"activities) in middle-aged and older adults confers areduced risk of functional limitations and disability inolder age. The reduction in risk for the effect of physicalactivity on a variety of outcomes related to function mostoften appears to be in the range of 30 to 50%.A modified scale [10] for the evaluation of quality of theprospective studies was employed (with the followingitems omitted: items 4, 5 and 8 in the reporting scale;items 12, 13 in the external validity section; 14, 15, and 19in the section on bias; items 21-26 relating to confound-ing; and item 27 addressing power). The final checklistwas made up of 12 items with a maximum score of 12points (with higher points indicating superior quality)rather than the original 32 points. The studies examinedwere of good quality scoring 8 to 12 (median 9) on themodified Downs and Black scale (Table s5, see additionalfile 3).The strength of the recommendations is related to aconsistency in the findings across studies. This strengthof evidence is underscored by the fact that there is a con-sistency of the effect of physical activity across a verywide range of outcome measures from disability in ADLor scores on quality of life or the SF36, to self-report diffi-culties in tasks like walking 400 m or taking a flight ofstairs, and to performance tests involving walking speed,chair rises or carrying a load. Furthermore the effect ofphysical activity has been demonstrated with short-termfollow-up of a couple of years as well as for long-term fol-low-up. In the former there is some concern that thephysical activity groups formed initially may have differedin undetected ways in "health status" and the physicalactivity effect was exaggerated; however, in the long-termfollow-up it is likely that the effect of physical activity isunderestimated in that in the initially designated activegroup it is likely that many became much less active overthe long-term follow-up and thus should have been in theinactive group. Nevertheless, an additional strength ofthe data comes from studies that assessed physical activ-ity at different time points and have shown that beingconsistently active was associated with a reduced risk offunctional limitations, a perhaps of even greater impor-tance that becoming physically active (from inactive inolder age) similarly reduced risk of functional limitations.A further reassurance is the evidence of a dose-responserelationship of physical activity level with the various out-comes of function.The included studies have some limitations. A clearweakness in the data available to date is in the limitationsof the physical activity assessments. Most studies havedefined as those who participated in a grouping of vigor-ous activities, to defining the active as the middle-tertileor even middle two quartiles of the physical activity"scores" of the sample. It is not possible to discern formost categorizations when a "high" or "moderate" physi-cal activity score was related to intensity of activitiesundertaken or a score from total volume of activities.Thus, whereas there appears to be a dose-response rela-tionship with physical activity and functional outcomesthe expression of this "dose" in terms of a recommenda-tion is not precise. Particularly, whereas there is data toshow that "higher" levels of physical activity are beneficialthere is not the data to support that "lower" physicalactivity levels are effective and thus there is need to estab-lish whether there is a minimal threshold of physicalactivity for benefit. In this aspect we reviewed only pub-lished literature and there is the possible publication biasof rejection of studies that did not show significantresults, which would be more likely if studies had com-pared light activity groups to sedentary rather than com-parisons of heavy or at least mid-range activity groups tothe inactive group. This bias in publication (that non-sig-nificant comparisons for light activity groups that mayhave been found would not get published) underscoresthe caution in recommending activities of less than mod-erate intensity and volume.Given the above analyses, there appears to be a dose-response effect that more activity has a greater effect butprecise categorization of a minimal or effective or sub-stantive dose is not clear cut. Critical evaluation and anal-ysis of each of the studies was required to attempt todiscern, or speculate, regarding any of the physical activ-ity details of type and mode, and duration or intensity ofthe activity in relation to outcomes. The studies with out-comes related to ADLs and disability, generally in olderage groups (baseline age >70-75 years), often assessedactivity level by participation in walking (>1 mile on eachsession, or "for exercise"), gardening and exercising. Thus,for individuals of these age groups, those classified asphysically active were doing some moderately-vigorousactivities and one would conclude that the requisite phys-ical activity level was high with conclusions such as walk-ing 1 hour/day, frequently walking > 1 mile, walking forexercise 20 min/day 3 times/week, walking and gardening100 min/day, optimally; nevertheless others did finddose-response trends suggestive that the middle-tertile ofphysical activity groups also had reduced risk of ADL dis-ability. In older groups (>70-75 years of age) frequentlywalking 1 mile or more appears effective in preventingdisability. Thus, for older groups (>70-75 years of age) theprevention of functional losses and limitations is metused just two categories of physical activity, sedentaryversus active, but there is a large variation in how thesecategorizations were derived from the active beingthrough physical activity levels equivalent to recommen-dations of walking or other activities 5 times/week for 30min (or 150 min/week) or more vigorous exercise walkingPaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 11 of 22of minimally 60 min/week (20 min, 3 times/week),although the dose-response data suggest that some lowerlevels of physical activity may also have influence in this"older" group.With regard to studies where the outcome was func-tional decline or functional limitation or ability to per-form or performance on "higher" level tasks, in six studies[21,36-39,41] in sample groups usually younger (60 to 70years of age at baseline) the active group were defined bya rather vigorous or a "high" level of activity and inanother group of studies with sample ages usually in their70s the protective activity was at least moderate (and usu-ally >4 times/week) [16,20,42,44-46,48]. Nevertheless in anumber of studies there was a dose-response relationshipof physical activity level (usually inactive, to moderate, tohigh) with the outcome [20,25,40,45-48]. Thus, moderateto higher levels of activity of at least 4 times/week or 180min/week are effective; although there may be an inversedose-response relationship of physical activity level withfunctional limitations and disability there remains thepossibility that there is a minimal threshold of at least a"moderate" activity level for a significant effect on out-comes. For younger groups (generally age 60-70 years)the activities proven effective were vigorous or at a highlevel, although again there was a noted dose-responsebetween moderate and heavy in a couple of these studies[20,25,45].Beyond the aspects of intensity or duration, or totalenergy expenditure, as Keysor [50] point out, it remainsunknown as to what aspects of physical activity (or exer-cise) behaviours are important in terms of disablementoutcomes, or for that matter functional outcomes. Thusas well as conventional physical activities or exercise,multi-factorial activities that include balance, endurance,trunk rotation, transfers, weight shift transitions andstrengthening may be effective as they relate directly tospecific functions or disabilities, but for the present onlyrecommendations of aerobic activities are supported bythe data. In this regard the physical activity of walkingseems ideal in direct relation to daily functions of olderindividuals and prevention of mobility disability. Never-theless, a host of aerobic activities are suitable includingother recreational activities (e.g., cycling), sport partici-pation (of an aerobic nature, e.g., squash, soccer, basket-ball, ice-hockey), or household chores of an aerobicnature (e.g., mowing the lawn).Recommendations The prospective cohort studies pro-vide evidence that a 50% reduction in risk of functionallimitations and disability is possible in more physicallyactive older individuals. The evidence of this relationshipis Level 2, Grade A. It appears that this degree of protec-descriptors equate moderate to higher levels of physicalactivity as about 30 to 60 min/day or totalling about 150to 180 min/week (and approximating 1000 kcal/week;4200 kJ/week) with intensity descriptors of moderatelyvigorous to vigorous or "walking for exercise" (Level 2,Grade A). Although there is a dose-response trend acrossat least moderate to high activity levels, a recommenda-tion of lower level (light) physical activity lacks evidenceand may be ineffective (i.e., a recommendation of lightactivity would be at Level 3 or 4, and Grade B). At pres-ent, based on prospective cohort studies, only recom-mendations of aerobic physical activities are supportedby the data, as there is little data regarding the relation-ship between strength-related activities and reduced riskof functional limitations (although there is evidence thatthese may be recommended in persons with clinical con-ditions, functional limitations, disability or frailty of oldage). Thus, from prospective studies a recommendationof strength-related activities would be Level 3 or 4 andGrade B.Cross-sectional and retrospective cohort studies of physical activity and functional limitations in older adultsInformation from cross-sectional observational studieslinking physical activity levels to functional measures wasreviewed but a complete systematic review and tabula-tion of the papers was not done as these studies showrelationships of physical activity to functions, but it isusually unclear as to whether a functional limitation pre-ceded or was consequent to a lower physical activity level.An important study relating physical activity and func-tional outcomes is that of Morey et al. [51]. In this studyof 161 men and women of mean age 72 years it wasshown that both lower cardiorespiratory fitness and mus-cle strength were associated with functional deficits(from self-reported functional abilities and a perfor-mance test) and thus lack of "fitness" was a critical modi-fier on the path to disability. Among the cross-sectionalstudies four that were reviewed had large subject samples(>2000 subjects). Brach et al. [45] for subjects over age 70years found that exercisers compared to life-style activeand inactive scored higher on the performance test bat-tery and a 400 m walk. Brown et al. [52,53] found thatsubjects age >65 years with physical activity levels of 3-4days/week or 5-6 days/week reported fewer "unhealthydays" than the inactive group (although 7 days/week andextensive vigorous exercise were negative in that "toomuch" predicted more unhealthy days). Simoes et al. [54]in subjects >60 years of age found a dose-response rela-tionship of physical activity to level of ADL and IADL dis-ability with the active group 45 to 60% less likely to reporta disability. Sulander et al. [55] examined a number oftive effect requires physical activity of moderate to higherlevels (or moderate to high cardiorespiratory levels),again supported by Level 2, Grade A evidence. The dosehealth behaviours and noted physical activity associatedwith poorer ADL functions in subjects aged 65 to 79years.Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 12 of 22Other studies reported relationships of moderate phys-ical activity with SF36 scores [56]; relatively high physicalactivity significantly related to lower ADL or IADL dis-ability [57]; and a better functional status index in thosewho "exercised" even a minimal amount [58]. Othersrelated fitness measures to functional performance withVO2max related to functional limitations [59]; aerobicexercise capacity explaining 25% of the variance of physi-cal function on the SF36 questionnaire [60]; VO2max, butnot strength, being related to SF36 scores [61]; andVO2max relating to ability to perform functional testsand ADL activities [62]. Additionally, cross-sectionalanalyses have related strength measures to various func-tional outcomes [59,62-65]. Overall, the cross-sectionalinformation relates physical activity or aerobic orstrength fitness to "better" functional measures, but thestudies essentially do not add to the determination of rec-ommended physical activity levels.Exercise training studies in older adults with functional outcomes: Aerobic programmes and "combined" programmesDescription of Studies (population, intervention, outcome) This systematic review also examined theinfluence of exercise training programmes on functionaloutcomes. Exercise training intervention studies, ofeither aerobic or aerobic supplemented with resistancetraining, are summarized in Table s6 (see additional file4). A total of 14 articles (14 unique data sets, and 3 sup-plementary reports) met the criteria for inclusion in theevaluation of the effects of aerobic training programmeson indicators of functional status in older adults. Thisincluded 1,938 unique participants with study sizes rang-ing from 13 to 582 (median n = 114). Five studies were offemale samples only, with the remaining including bothmen and women. The median training duration of thestudies (excluding a study that used a 10-year telephonebased follow-up [66]) was 24 weeks. Ethnicity was gener-ally not reported explicitly. However, data were obtainedfrom studies from a variety of countries and regionsincluding the USA (8), Canada (2), Japan (2), Turkey (1),and Greece (1). The articles were published between 1996and 2009.Results, Data From exercise training programmes thefunctional outcomes include changes in physical perfor-mance functions such as walking speed/distance, or self-report functional abilities such as physical functionassessed by the SF36. To date these studies have usedproximal outcomes taken at the end of the training pro-gramme; but, the effects on distal outcomes, whetherimpairments and functional limitations, or disability areitations in older persons after aerobic or combined exer-cise training.The pilot data reported by Pahor et al. [67] is perhapsmost important to date. A combined exercise programmefor ~400 men and women of mean age 77 years reporteddata up to 12 months. The physical activity programmeresulted in higher physical performance scores; and thisstudy used the 400 m walk as an indicator for mobilitydisability finding that there was a lower incidence of theinability to complete the walk in the physical activitygroup versus an educational control group, with an oddsratio of 0.71 approaching significance in this pilot data.Thus, this study has examined the proximal outcomes ofa 12 month programme, but with a measure that is anindicator of disability rather than just functional mea-sures.Interpretation The quality of the studies reviewed issummarized in Table s7 (see additional file 5). For RCTstudies, a modified scale was employed (with the follow-ing items omitted: item 13 in the external validity section;14 in the section on bias; item 24 relating to confounding;and item 27 addressing power). The final checklist wasmade up of 23 items with a total score of 24. For non-RCT studies, a modified scale was employed (with thefollowing items omitted: item 13 in the external validitysection; 14 in the section on bias; items 23 and 24 relatingto confounding; and item 27 addressing power). The finalchecklist was made up of 22 items with a total score of 23.The median score of the 10 RCT studies was 21 of a pos-sible 24, thus the studies were of good quality. For thefour non-RCT studies the median was 17.5 of a possible23.It is not possible to clearly define the minimal volumeand intensity of exercise training required to elicit theimprovements in functional status owing to the variabil-ity in the methodologies employed and the lack ofdescriptive information regarding the volume of activityin many studies. Indeed the majority of the studiesemployed moderate intensity aerobic exercise for 3 days/week and generally 30 to 45 min/session.Thus, in overview, training interventions of aerobicexercise and walking programmes are effective inimproving functional abilities. Additionally there are alarge number of studies measuring an improved physio-logical outcome (VO2max) with training, but not a func-tional outcome (see [2]). The exercise training studies dodemonstrate that a short-term exercise programme inolder adults is effective, and thus add to the informationfrom prospective follow-up studies wherein a physicallyactive lifestyle is presumed to have been a characteristicof an individual over the long-term and thus implicatingnot as apparent (Table s6, see additional file 4). Nonethe-less, the literature was consistent in supporting thereduction in the risk for functional impairments and lim-that lifelong activity was needed. There is some expressedconcern that a physiological improvement or animproved score on functional abilities may not translatePaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 13 of 22to prevention of physiological limitations or future dis-ability; however, the link between physiological and func-tional limitations has been established in the cross-sectional studies. And the prospective cohort study ofPaterson et al. [5] showed a relationship of VO2max withsubsequent dependent living.Recommendations Thus, the prospective studies pro-vided evidence regarding a long-term lifestyle of physicalactivity, whereas these exercise training interventions addthat a short-term physical activity intervention (exerciseprogramme of moderate intensity, 3 times/week) is alsoeffective (and adds to prospective study conclusions) inreducing functional impairment or limitation with Level2, Grade A evidence. It is also notable that functional out-comes were more greatly affected using combined aero-bic and muscle resistance exercise programmes [68,69].Thus resistance training of older adults appears to com-plement aerobic physical activity benefits, and could be arecommended adjunct to a physical activity programme,but at Level 3, Grade B.Exercise training studies in older adults with functional outcomes: Resistance training programmesDescription of Studies (population, intervention, outcome) Exercise training intervention studies of pro-grammes of resistance training (or muscle function train-ing) are summarized in Table s8 (see additional file 6). Atotal of 17 articles met the criteria for inclusion in theevaluation of the effects of resistance training pro-grammes on indicators of functional status in older adults(Table s8, see additional file 6). This included 845 uniqueparticipants with study sizes ranging from 10 to 124(median n = 40), and 11 studies included both males andfemales with six of females only. The average trainingduration of the studies (excluding a study that used a 7.7year follow-up [70] was approximately 24 weeks (rangingfrom 6 to 72 weeks). Ethnicity was generally not reportedexplicitly. However, data were obtained from studies froma variety of countries and regions including the USA (9),UK (3), Canada (1), Chile (1), Italy (1), Austria (1), andSouth Africa (1). The articles were published over a 12year period ranging from 1995 to 2007.Results, Data Similar to the aerobic training literature,the effects of resistance training programmes on disabil-ity are not as apparent as the more immediate measuresof effects on functional impairments and limitations. Ingeneral the subject groups were of mean age between 70and 80 years, and most studies of 6 to 24 weeks showedchanges in strength or muscle power in various musclegroups. With regard to functional outcomes, there wassome compelling evidence that moderate intensity resis-tance training was effective in improving functional sta-moderate intensity (50% of 1 RM (repetition maximum)or moderate weights allowing 12-15 repetitions), therewere improvements on a number of functional abilities[71] or specific functions such as a chair rise test [74] orstair climb [75]. Nevertheless four studies [68,76](reported on Table s4, see additional file 2); [73,77] eachof greater than 16 weeks and relatively heavy resistancetraining programmes showed adequate strength gains butmarginal or no improvement in various functional per-formances. Other studies listed in Table s8 (see additionalfile 6) also did not clearly demonstrate substantial func-tional changes.Interpretation As reviewed in Table s9 (see additionalfile 7) the resistance training studies were on average offair to good quality with RCT studies scoring a median of17/24 and non-RCT 15/23. (As per the aerobic table, forRCT studies, a modified scale was employed with the fol-lowing items omitted: item 13 in the external validity sec-tion; 14 in the section on bias; item 24 relating toconfounding; and item 27 addressing power. The finalchecklist was made up of 23 items with a total score of 24.For non-RCT studies, a modified scale was employedwith the following items omitted: item 13 in the externalvalidity section; 14 in the section on bias; items 23 and 24relating to confounding; and item 27 addressing power.The final checklist was made up of 22 items with a totalscore of 23.)However, in summary, as in a detailed in a review byLatham et al. [78], although progressive resistance inter-ventions in older people yield increases in strength andcan have a positive effect on some functional limitations,the evidence of improved functional performances iscontroversial, and the effect on substantive outcomes ofdisability or aspects of health are not clear. Resistancetraining alone (i.e., without the aerobic training recom-mendations) does not seem to be a supportable recom-mendation for functional outcomes, or for morbidity ormortality in older adults (although a greater muscle massmay be associated with reduced mortality reportedly sec-ondary to a reduced risk of type 2 diabetes).Recommendations Thus, progressive resistancestrength programmes may yield improvements in someselected functional tasks but to date it cannot be con-cluded that these will result in reduced functional limita-tions or disability. If a recommendation of resistancestrength programmes based on the evidence from thesetraining interventions were to be made it would be atLevel 3, Grade B or C.Mechanisms of the relationship of physical activity and functional limitationsThere are plausible mechanisms to explain a relationshiptus in older adults. Five studies [71-75] showed that withtraining programmes ranging from 6 weeks to one year,and resistance training programmes that ranged frombetween physical activity and lower risk of functionallimitations. Randomised control trials of exercise pro-grammes show improvements in physiologic capacityPaterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 14 of 22related to aerobic fitness, muscle strength and power andalso improved functional abilities. Lang et al. [39] sug-gested a number of factors: i) physical activity may relatespecifically to physical function; for example musclestrength may have a mediating role between physicalactivity and disability; ii) physical activity is protectiveagainst the metabolic syndrome thus reducing incidenceof conditions whose consequences include reduced phys-ical function; iii) exercise and physical activity are associ-ated with lower inflammatory markers in older adults andmay reduce the damaging effects of inflammation,including those associated with excess adipose tissue; iv)physical activity provides psychological benefits; v) physi-cal activity may maintain body weight and strength (andmitigate against age-related loss of lean body mass).Boyle et al. [33] also suggested mechanisms that mayunderlie the complex association between physical activ-ity and disability. They included the effects of: improvedaerobic capacity, muscle strength, and flexibility; protec-tion against development and progression of disablingconditions (diseases such as cardiovascular, respiratory,osteoporosis, as well as nerve growth factors relating tocognitive function and protection against ischemic andneurotoxic damage); and, favourable psychologicaleffects.As noted earlier, a variety of recreational, sport orhousehold activities may be appropriate for aerobic exer-cise. And as a caveat to recommended physical activitiesregarding sex difference - in older women exercise train-ing yields minimal change in heart stroke volume (centraladaptation, see [79]); thus specificity of exercise program-ming to the muscle groups used in mobility of daily activ-ities is important. Walking is of course specific, and anactivity such as cycling would probably have carry-over toaerobic adaptations in muscle groups used in mobility ofdaily activities, whereas swimming (arm exercise) lacksthe specificity and would not be a recommended activityfor older women wishing to gain aerobic fitness foraccomplishing daily functions.Cognitive FunctionSearch Results: Physical Activity and Cognitive FunctionA total of 861 citations were identified during the elec-tronic database search (Figure 4). Of these citations, 180were identified in MEDLINE, 512 in EMBASE, 49 inCochrane, and 120 in the CINAHL/SportDiscus/PsychInfo search. A total of 37 duplicates were found,leaving a total of 824 unique citations. A total of 747 arti-cles were excluded after scanning, leaving a total of 77articles for full review. From these articles 45 wereexcluded after full review leaving 32 articles for inclusionclinical population) or for life-style (community-dwell-ing); functional measure not reported; physical activitylevel or exercise capacity not reported; the citation was areview, dissertation, thesis, or abstract.A total of 32 articles met the criteria for inclusion in thesystematic review of the literature regarding the relation-ship between physical activity and cognitive function inolder adults (Table s10, see additional file 8). Additionalliterature was tracked from reference citations and authorfiles. These searches provided an additional 2 citations.Therefore, a total of 34 articles were included in the sys-tematic review of the literature regarding the relationshipbetween physical activity and cognitive function.Figure 4 Results of the literature search for cognitive function.Citations from electronic database search: MEDLINE   180 EMBASE   512 Cochrane   49 CINAHL/SportDiscus/PsycInfo 120  Total Citations Downloaded to RefWorks: Total in RefWorks  861 Total with Duplicates Excluded (N = 824)Articles Excluded after Full Review  (N = 45) Articles Included (N = 32) Articles Included from Search of Biographies and Authors Knowledge of Area (N = 2) Total Articles Included (N = 34) Full Articles Assessed for Eligibility after Scanning Titles (N = 77) Citations Excluded after Scanning Titles (N = 747) in the systematic review. The reasons for exclusionincluded: participant group did not meet the inclusioncriteria for age, absence of disease (i.e., study was of aDescription of Studies (population, intervention, outcome) The systematic review captured articlesanalysing associations between physical activity or car-Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 15 of 22diorespiratory or muscle fitness and a cognitive functionoutcome and included prospective cohort studies, cross-sectional studies, and exercise training intervention stud-ies. These studies included 19,988 participants with studysizes ranging from 14 to 4,615 participants. Ethnicity wasgenerally not reported explicitly. However, data wasobtained from studies from a variety of countries andregions including the USA (15), Australia (6), Canada (1),Turkey (1), France (1), Brazil (1), UK (2), Sweden (1),Japan (1), Greece (1), Italy (1), Nigeria (1), Netherlands(1), and a combination of countries (Finland, Italy and theNetherlands). The articles were published over an 18 yearperiod ranging from 1989 to 2007.The "intervention" of interest was physical activity.Physical activity reports were almost all from self-reportquestionnaires, and a few studies used cardiorespiratoryfitness measures, or strength measures, to relate to cogni-tive function. The physical activity descriptors used totalamount of activity, categories of frequency of participa-tion, or intensity of activities to categorize groups.There was considerable variability in the measuresemployed to evaluate cognitive function, which made theinterpretation of the findings difficult. In fact, there wasno consistent battery of tests to evaluate cognitive func-tion. Measures may have included cognitive speed (e.g.simple reaction time, choice reaction time), visual mem-ory (e.g. Wechsler Memory Scales visual reproduction,Benton visual retention test), verbal memory (e.g. Randtmemory test, Weschler memory scale), motor function(finger tapping), working memory (e.g. digit span tests),perception (face recognition), executive functions (e.g.verbal fluency, problem solving, word comparison), cog-nitive inhibition (e.g. Stroop test), visual attention (e.g.letter search, visual search), and auditory attention (e.g.Digit span forward).Results, Data The majority of the articles (24 (71%))demonstrated a positive relationship between physicalactivity/fitness and indices of cognitive function.Nine studies provided prospective "follow-up" cohortdata with 7 (78%) of these demonstrating a positive rela-tionship between the physical activity level and cognitivefunction outcomes. The two negative studies did not finda relationship to cognitive performance or impairmentrelated the amount of walking or sports [80] and a contin-uous 0-70 point activity scale [81]. The positive studieshad physical activity descriptors of physical activity ornot [82], walking greater than 2 miles per day (versus lessthan 1 mile [83]), engaging in a number of activities [84],or various activities more versus less than 3 times perweek [85], or for less than 30 up to greater than 120 min/day [86], and high intensity versus low or moderate inten-delayed onset of dementia. In overview from these stud-ies it would appear that positive cognitive outcomes aregenerally associated with a "higher" amount or intensityof physical activity.The literature that employed an exercise intervention(n = 12) provided some controversy in the findings. Aslight majority of these studies (7 (58%)) demonstrated apositive effect on at least one measure of cognitive func-tion. These studies employed moderate intensity aerobicphysical activity interventions; however, it is difficult toquantify the actual volume of exercise used in each inter-vention. The positive studies generally showed smallchanges in usually just one or two cognitive measures.One study showed some beneficial cognitive functionsscores with either moderate or higher intensity resistancetraining over 24 weeks [89]. Nevertheless in the negativestudies the exercise intervention appeared to be verygood and the finding of no significant change in outcomecognitive function measures extended across a number ofvariables. Thus, each of the negative studies appeared tobe well-conducted [90-93]. Other studies in the cognitivefunction category were of a cross-sectional nature andagain mixed results were found as to whether there was arelationship of physical activity level, or fitness level, withcognitive function measures. Therefore, there is mixedevidence to support or refute the benefits of habitualphysical activity and/or exercise training on cognitivefunction in older individuals.Interpretation The quality of investigations was evalu-ated for the various studies (Table s11, see additional file9). The Downs and Black [10] scale was varied accordingto the different types of study designs (as described ear-lier). Of the prospective/longitudinal designs, the studieswere of generally good quality ranging from 8 to 11(median 10.0 out of a possible 12). The randomised con-trol trials were varied in quality ranging from 15 to 19(out of possible score of 24) with a median score of 17.5.The non-randomised control intervention trials and thenon-prospective cohort trials were generally of lowerquality (median 15.0 out of 23) with a range of 14 to 17. Itis important to note that there is insufficient data to con-clude that a change in aerobic or musculoskeletal fitnessis required to elicit positive changes in cognitive function[94,95]. Some evidence does however demonstrate posi-tive changes in cognitive function with improvements inboth aerobic [96] and musculoskeletal [89,97] fitness [95].Moreover, and more convincing, there is consistent evi-dence that habitual physical activity reduces the subse-quent risk for dementia and Alzheimer's disease inhealthy older individuals [82,84,85,98].Recommendation It would appear that habitual (long-sity [87], or grouped by fitness tertile [88]. The positiveoutcomes ranged from better cognitive function, to lesslikely to develop dementia or Alzheimer's disease, or aterm) physical activity is associated with a decreased riskof dementia and Alzheimer's disease, with the evidenceLevel 2 and grade A. It would also appear exercise train-Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 16 of 22ing can result in an improvement in cognitive function inhealthy older adults. However, these conclusions must betempered owing to the balance of negative and positivestudies and considerable variability in the battery of testsused to measure cognitive function. Thus, it appears thatthere is a relationship between physical activity (probablyof a relatively "high" level of physical activity) and bettercognitive function outcomes; however, to date it cannotbe concluded that an exercise training programme willnecessarily maintain or improve cognitive function or inthe longer-term alter the course of dementia. To make arecommendation for a "standard" aerobic or resistancetraining programme to affect cognitive function of olderadults would at the moment be at Level 3, Grade B.Other factors to be considered related to physical activity recommendationsWhat other factors should be considered in recommen-dations of physical activity for older adults?Stretching and flexibility exercises, primarily for shoul-der and hip joints, may have some benefit in relation tofunction and may be recommended in rehabilitationwhere joint range of motion has been compromised bydisuse or injury, but in general a recommendation of flex-ibility exercises is not supported by the scientific litera-ture. Thus, although greater flexibility may facilitate someaspects of daily life, and stretching activities are incorpo-rated into most physical activity programmes there are noknown health benefits of greater flexibility and stretchingexercises have not been demonstrated to reduce risk ofactivity-related injuries or reduce post-exercise musclesoreness. In fact pre-performance stretching exerciseshave been shown to reduce scores on some performance-related tasks (see [99]). Observation of many older adultactivity classes and programmes gives evidence of aninordinate emphasis on flexibility and at the expense ofaerobic and strength programming; thus in guidelines orrecommendations it may be prudent to discouragespending an excessive amount of time in flexibility exer-cises and suggest stretching exercises be done at the con-clusion of an activity session.On the other hand a general whole body warm-up bygradually increasing the physical activity intensity up tothat of the exercise session target level is advisable, and agradual cool-down back toward baseline is a prudentsafety factor to avoid "pooling of blood in the periphery"and potentially depriving the heart and brain of neededblood flow.Comments on starting a programme of increased phys-ical activity are also warranted. Often at the start of a pro-gramme it is not possible or feels too demanding to meetapproach) to begin at a lower intensity and duration of aphysical activity session (either in relation to aerobic orresistance exercises) and then incrementally progress tomeet the duration goal and subsequently the intensitygoal. Nevertheless research has shown that older adultsdo adapt physiologically to a given imposed exercisestress over a similar time frame to that observed inyounger individuals [100]. Further exercise training pro-grammes of community-dwelling older adults have beensafe and effective with progression to 70% VO2max (vig-orous exercise) within one or two weeks (and similarrapid progression in resistance training). If one starts toolow and has a minimal "overload" the adaptation will besmall, and if progression is too slow one loses the motiva-tion of seeing and feeling, the "improvements" and gain infitness and function; reward of improvement likely helpsmaintains adherence to the activity programme.Integration of Data from Different Study Designs and Different "Health" OutcomesStudies of the relationship between long-term physicalactivity and morbidity and mortality outcomes werereviewed in the "adult" paper [1] and the previous reviewspecific to older adults [2]. With regard to achieving areduced risk of various morbidities, or of all-cause mor-tality, the recommended physical activity was of a moder-ate (brisk walking was a descriptor) with a total volume of150 to 200 min/week to moderately-vigorous intensity(with >4.5 METS recommended, but scaled relativelylower in older adults) and volume of 90 min/week, andenergy equivalent approaching 1000 kcal/week. Higherintensity was seen to engender additional benefit. Therewas little evidence to support the concept of accumulat-ing or "counting-up" light, moderate short-duration activ-ities like walking (here and there during the day), or shortduration non-aerobic activities (taking stairs), or smallmuscle group activities (like raking leaves, or painting awall). Evidence does support 10-min segments of "exer-cise training" being additive [101].From the point of view of maintaining cardiorespira-tory fitness above important functional thresholds (per-formance-related fitness) and postponing functional loss,the earlier review [2] determined that this could beachieved with a moderate exercise programme of 150min/week or vigorous exercise of 90 min/week, but thatlight intensity activity or an accumulated volume of activ-ity throughout the day was not effective in maintaining orincreasing cardiorespiratory fitness of older adults.The present systematic review focused specifically onfunctional independence outcomes. It is concluded thatreduced risk of functional limitations and disability inthe recommended guidelines. Although scientists havenot established a standard for how to gradually increasephysical activity over time it is prudent (and a safeolder age can be achieved with moderate and moderately-vigorous physical activity, but not light activity, with avolume of 150 to 180 min/week or approximately 1000Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 17 of 22kcal/week (4200 J/week) energy expenditure, and takingup physical activity or undertaking an exercise pro-gramme, usually of moderate intensity in the range of 150min/week to moderately-vigorous aerobic exercise of 30min/session and 3 times/week, is effective. There was adose-response with greater volume in either the moder-ate or vigorous domain yielding further reduction in rela-tive risk of functional limitations or disability.Exercise intervention studies have also shown thatresistance training of 2 times/week of the major musclegroups is recommended to preserve muscle mass andmaintain strength and power for daily activities, andresistance training also receives some support from datarelated to morbidity and mortality outcomes. Physicalactivity appears also to have a role in prevention ofdementia, and exercise interventions appear to improvesome aspects of cognitive function, however statement ofthe details of the requisite dose of activity to achievethese benefits is to date premature. Thus, information islacking to determine the dose of physical activityrequired for cognitive benefits or to modify the recom-mended activity levels based on the other outcome vari-ables.There is some concern that "significant" effects of phys-ical activity were derived from studies in which the com-parison was between the most sedentary groups and amoderate to moderately high active group and once a rec-ommended physical activity level was established subse-quent studies compared those below to those above therecommended level. Thus these cut points for active ver-sus inactive have produced a "line in the sand" and a self-fulfilling prophecy that further studies would concur.Nevertheless, as reviewed, there are studies that haveexamined lighter volume or intensity of activities and notfound a "meaningful" reduction in risk of the outcomevariable and in studies examining a number of physicalactivity groups and noting a "significant" trend the con-cept of a dose-response has generally been that more vol-ume in the moderate or moderately vigorous domains hashad a greater effect. Thus, there is not the data to supporta recommendation below the present commonly citedintensity levels, and it is reassuring to note that if the rec-ommendation is "higher" than some minimum thisgreater dose is associated with a greater response - it isbeneficial (there is a "response") to do more above a mini-mum or moderate level. It might also be noted that estab-lishment of any minimum at present would be derivedfrom comparison with a "least-active" group, whereas therecommendations are for physical activity above an indi-vidual's present baseline. Perhaps from a public healthperspective it is prudent to note that there is a dose-the more active segments of the population will all bene-fit from increasing their own physical activity levels.How are moderate and vigorous interpreted in guidingphysical activities for older adults? The following exam-ples of what have been described as moderate and vigor-ous walking paces for older adults may help clarify themoderate and vigorous recommendations and the recom-mendations of total volume or energy expenditure perweek:• Moderate intensity walk of 3.0 mph = 3.3 METS =11.6 ml/kg.min = (at 60 or 80 kg) ~700 - 900 ml/min VO2(or 3.5 - 4.5 kcal/min) = ~46-58% VO2max (for olderadult VO2max in the range of 20-25 ml/kg.min); and 180min/wk = 630 - 810 kcal/wk = 594 MET.min.• Vigorous intensity walk of 4.0 mph = 4.2 METS = 14.7ml/kg.min = (at 60 or 80 kg) ~ 880 -1180 ml/minVO2 (or4.4 - 5.9 kcal/min) = ~59-74% VO2max (for older adultVO2max in the range of 20-25 ml/kg.min); and 150 min/wk = 660 - 885 kcal/wk = 630 MET.min.It should be noted that there is good evidence that thephysiological and performance responses of older adultsat a given "relative" intensity are similar to those of youngadults. It has been demonstrated that performance timeat a given intensity relative to VO2max, or to other rela-tive intensity markers is similar in older adults to thatobserved in younger samples [102]. Thus, recommendingexercise at a percentage of VO2max, or relative to othermarkers of exercise intensity in older adults is relativelysimilar to the recommendation for younger adults. Forexample, Overend et al. [103] documented similarachievement of quasi-steady state physiologicalresponses with 24 minutes of exercise at critical power(highest sustainable exercise rate) in older compared toyounger individuals, and in fact the older adults per-formed at approximately 90% of their VO2max comparedto 85% of VO2max in young. Additionally, the "anaerobic"threshold (or estimated lactate threshold or gas exchangethreshold) usually occurs at a higher percentage ofVO2max for older versus younger adults (due to a greaterage-related rate of loss in VO2max versus the thresholdmeasure, e.g. Paterson et al., [104]) and thus relative tothis marker of the intensity for sustained steady stateexercise the recommended relative intensity could evenbe somewhat higher in older versus younger individuals.It should also be noted, however, that whereas physicalactivity recommendations in younger adults may halvethe volume of vigorous activity versus moderate activity,in older adults there is a "narrow scale" between moderateand vigorous such that a vigorous intensity is much lessresponse such that the least active or the average or even than twice the moderate dose and one-half of the volumeof vigorous does not yield a similar volume to that ofmoderate.Paterson and Warburton International Journal of Behavioral Nutrition and Physical Activity 2010, 7:38http://www.ijbnpa.org/content/7/1/38Page 18 of 22ConclusionsDose of Physical Activity - Recommendations for Older AdultsThe present systematic review emphasized the relation-ship between physical activity and functional indepen-dence and cognitive function outcomes in older adults.The data support the physical activity recommendationsderived from analysis of the relationship between physi-cal activity and morbidity and mortality outcomes. Thesedata support the following recommendation:Physical activity (above baseline "normal" daily activ-ity levels) at an intensity of moderate to moderatelyvigorous aerobic (endurance) activity (3.3 to 4.2METS; 3-4 mph walk; >50%VO2max), with a totalweekly volume of 150 - 180 min/wk (3 hours at mod-erate pace or 2.5 hours of a more vigorous "brisk"walking, or other types of aerobic activities, with eachphysical activity session of greater than 10 minutes)and, a gain of 0.5 MET (~2 ml/kg.min) in cardiorespi-ratory fitness.This physical activity would translate to a >30%decrease in the relative risk of morbidity and mortality,and loss of independence, and further benefit wouldaccrue with greater physical activity and greater fitnessgains (~60% reduction in risks).Additionally, intervention studies of aerobic exercisetraining programmes for older adults support this inten-sity and amount of exercise as being effective in prevent-ing functional limitations and potentially delayingmobility disability in older age. Exercise training inter-ventions that supplemented the aerobic exercise byincluding twice per week "resistance" exercises of majormuscle groups support a recommendation that there maybe additional benefit in including resistance exercise (asan adjunct to the aerobic physical activity) to counter theage-related loss of muscle mass, and maintain thestrength and power requirements needed in daily activi-ties and to prevent falls.These short-term intervention studies of exercise train-ing have also suggested that the short-term response ofimproved fitness may translate into longer-term adher-ence to increased physical activity and thus it is appropri-ate for older adults to take up exercise to "Get Fit forActive Living" [105], and for physically active older adultsto maintain their activity and fitness levels to postponefunctional losses.Additional materialCompeting interestsDP and DW declare no competing interests.Authors' contributionsDP was the principal author of the text. DP also took responsibility for staffinvolved in cross-reference searching and adding these papers to the dataextraction tables, and quality assessment of the studies (prospective, aerobic,resistance). DP and staff produced and edited the final manuscript.DW took responsibility for the staff involved in the electronic search and prepa-ration of the initial data extraction tables, cross-referencing for the cognitivesection, and the quality assessment of the papers in the cognitive section. DWprovided the initial authorship of the search methods and of the cognitivefunction section. DW assisted in reading and editing of the final manuscript.AcknowledgementsProduction of the paper has been made possible through a financial contribu-tion from the Public Health Agency of Canada. The views expressed herein do not necessarily represent the views of the Public Health Agency of Canada. The leadership and administrative assistance was provided by the Canadian Soci-ety for Exercise Physiology. The authors gratefully acknowledge the large vol-ume of work undertaken by the staff: Lindsey Nettlefold (PhD candidate), Sarah Charlesworth (PhD), and Liza Stathokostas (PhD) and Juan Murias (PhD candi-date). Dr. Paterson's research is supported the Natural Sciences and Engineer-ing Council (NSERC, Canada). Dr. Warburton is supported by scholar/salary awards from the Canadian Institutes of Health Research and the Michael Smith Foundation for Health Research.Author Details1School of Kinesiology, University of Western Ontario, London, Ontario, Canada, 2Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada, 3Cardiovascular Physiology Rehabilitation Laboratory, University of British Columbia, Vancouver, British Columbia, Canada and 4Experimental Medicine Programme, University of British Columbia, Vancouver, British Columbia, CanadaReferences1. Warburton DER, Charlesworth S, Ivey A, Nettlefold L, Bredin SSD: A systematic review of the evidence for Canada's Physical Activity Guidelines for Adults.  Int J Behav Nutr Phys Act 2010, 7:39.2. Paterson D, Jones G, Rice C: Ageing and physical activity: evidence to Additional file 1 Supplemental tables 1-3. Table s1: Results of literature MEDLINE search regarding the relationship between physical activity/exer-Additional file 2 Supplemental table 4. Table s4: Prospective (longitudi-nal) cohort studies examining the relationship between physical activity and functional limitations in older adults [106-110].Additional file 3 Supplemental table 5. Table s5: Prospective studies assessed with the modified Downs and Black Quality Assessment Tool.Additional file 4 Supplemental table 6. Table s6: Aerobic or combined exercise training studies examining the relationship between physical activity and functional limitations in older adults [111-121].Additional file 5 Supplemental table 7. Table s7: Aerobic or combined exercise studies assessed with the modified Downs and Black Quality Assessment Tool.Additional file 6 Supplemental table 8. Table s8: Resistance/strength or functional training studies examining the relationship between physical activity and functional limitations in older adults [122-130].Additional file 7 Supplemental table 9. Table s9: Strength studies assessed with the modified Downs and Black Quality Assessment Tool.Additional file 8 Supplemental table 10. Table s10: Studies examining the relationship between physical activity and cognitive function in older adults [131-148].Additional file 9 Supplemental table 11. Table s11: Cognitive studies assessed with the modified Downs and Black Quality Assessment Tool.Received: 16 July 2009 Accepted: 11 May 2010 Published: 11 May 2010This article is available from: http://www.ijbnpa.org/content/7/1/38© 2010 Paterson and Warburton; licensee BioMed Central L d. is an Open Access article distr buted under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.International J urnal of Behavi ral N trition and P ysical Activity 2010, 7:38develop exercise recommendations for older adults.  Can J Public Health 2007, 98:S69-S108.cise and functional limitations in the elderly. Table s2: Results of literature MEDLINE search regarding the relationship between physical activity/exer-cise and cognitive function in the elderly. 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