Impact of physical and psychological resourceson functional autonomy in old age

PASQUALINA PERRIG-CHIELLO1, WALTER J. PERRIG1,

ANDREAS UEBELBACHER1, & HANNES B. STAHELIN2

1Institute of Psychology, University of Berne, and 2Geriatric Clinic, University Hospital, University of

Basel, Switzerland

AbstractFunctional autonomy is a core condition of successful ageing. To maximize autonomous functioning isnot only a claim of social policy but also primarily an individual need. Part of the challenge ofpreventing unnecessary dependence in old age is to recognize the diversity among the elderly and thedifferent availability of their physical, psychological and social resources. The aim of this study is toexamine the age- and time-related changes in functional autonomy (activities of daily living, ADL, andinstrumental activities of daily living, IADL) and the psychophysical resources correlated with thesechanges in a sample of 441 healthy elderly persons aged 65 – 95. Furthermore, we are interested in thelong-term predictive power of physical resources (objective and subjective health, physical strength)and psychological resources (memory) on functional autonomy. Results show significant age- andtime-related deteriorations in functional autonomy and in most psychophysical resources. Structuralequation model analyses were performed to test the long-term predictive power of these resources.Results suggest that ADL is better predicted by physical resources than by psychological ones, but forIADL the reverse is the case; here memory variables play a dominant role. Physical and psychologicalvariables are thus specifically related to different components of functional autonomy. This has to betaken into account in the development of preventive and intervention programmes.

Keywords: Functional autonomy, health, memory, well-being, muscle strength, old age

Introduction

The demographic changes of the last decades have led to a substantial increase in the years

of later life (Grundy & Bowling, 1999). Considering the fact that old age is a period of life,

which contains an increased risk of becoming dependent, the maintenance of independence

and the fostering of autonomy has become a high priority public health issue.

The interest in promoting autonomy until very old age is not only related to the

demographical changes, it has also psychosocial reasons. In western society, a possible loss

of autonomy is considered as more distressing than ever before. The reason why is twofold:

(a) establishing and maintaining autonomy is a highly valued goal in western society and

therefore a central developmental task throughout an individual’s life-span—thus a loss of

autonomy is perceived as a painful and sorrowful experience. (b) In our modern

individualistic society, social networks and family ties are not as solid as they used to be

Correspondence: Pasqualina Perrig-Chiello, Universitat Bern, Institut fur Psychologie, Muesmattstr. 45, CH-3000 Bern

9/Switzerland. Tel/Fax: þ41-(0) 61-331 75 19. E-mail: Pasqualina.perrigchiello@psy.unibe.ch

Psychology, Health & Medicine,

November 2006; 11(4): 470 – 482

ISSN 1354-8506 print/ISSN 1465-3966 online ª 2006 Taylor & Francis

DOI: 10.1080/13548500600726633

in the past—loss of autonomy therefore mainly means institutionalization (Hopflinger &

Hugentobler, 2003). We can thus infer that functional autonomy is closely related to

psychological well-being and considered a core condition of successful ageing. It has been

postulated that independent living is the essence of human functioning because it promotes

physical and psychological health (Coleman & Iso-Ahola, 1993; Deci & Ryan, 1987).

Research results indicate that the ability to be self-determined and to exercise control over

one’s life is critical to both psychological and physical well-being and health (Perrig-Chiello,

Perrig, & Stahelin, 1999; Searle, Mahon, & Iso-Ahola, 1995; Searle, Mahon, Iso-Ahola,

Sdrolias, & van Dyck, 1998).

A review of literature reveals that the majority of elderly people maintain their functional

autonomy,1 although considerable individual differences can be observed. Functional

autonomy can be defined on different levels. The basic components of an autonomous life

are the activities of daily living (ADL: eating, dressing, personal hygiene and body care,

moving around; Baltes, Maas, Wilms, & Borchelt, 1996; Baltes, Mayr, Borchelt, Maas, &

Wilms, 1993). These basic competencies are highly automatized and necessary for survival,

they are universal, free from cultural influences and only partly dependent on socio-

demographic, psychological and economical factors—but they are, however, strongly

determined by objective health. If they are restricted, physical dependency and need of care

result. The other crucial components of autonomous living, the instrumental activities of daily

living (IADL), are more complex than ADL and correspond to the expanded competencies

of daily activities (mobility, i.e., moving around on foot, by car, shopping, house-keeping)

(Baltes et al., 1993, 1996). Since this component does not depend primarily on physical

resources (e.g., health status), but essentially on psychosocial factors such as socio-economic

status (Andrieu et al., 2002), cultural and ethnical belonging (Carrasquillo, Lantigua, &

Shea, 2000), cognitive capacity (Sousa & Figueiredo, 2002; Steeman, Abraham, &

Godderis, 1997) and personality variables (Curyto, Chleski, & Lichtenberg, 1999; Sousa

& Figueiredo, 2002), large interindividual differences can be observed. If these IADL are

limited, behavioural dependency is the result.

Several scientific approaches explain the various pathways of aetiology of dependency

(impairment approach) or maintenance of autonomy (resource approach). Traditionally, the

impairment approach has tried to explain the aetiology of dependency in terms of decreasing

levels of ADL and IADL by using pathogenic models (Verbrugge & Jette, 1994). These

studies have indicated a very complex relationship between physical and psychological risk

factors for dependence such as physical and sensory impairments, pain, dementia or

depression (Johnson, Kramer, Lin, Kowalsky, & Steiner, 2000; Mossey, Gallagher, &

Tirumalasetti, 2000). In a study by Steeman and collaborators (1997), risk profiles for the

institutionalization of elderly people were identified. High-risk profile persons were not only

highly dependent in ADL, but in addition had severe cognitive impairments, poor

communication skills and behavioural problems (Steeman, Abraham, & Godderis, 1997).

More recently, resource-oriented approaches have focussed more on the processes that

predict the maintenance of autonomy (Baltes et al., 1993, 1996; Grundy & Bowling, 1999).

Here the identification of protective factors, such as physical activity, social contacts, life-

skills, psychological well-being, but also good cognitive functioning, are at the centre of

interest (Heathcote, 2000; Miller, Rejeski, Reboussin, Ten-Have, & Ettinger, 2000;

Topinkowa, 1999). Resource-oriented approaches have the advantage of emphasizing the

multidimensional nature of the maintenance of functional autonomy and of exploring the

related intervention possibilities (Peter-Wuest, Stuck, Dapp, Nikolaus, Goetz, Gillmann,

et al., 2000). However, the state of the art of research is far from being consistent. A review

of the large amount of studies on predictors of functional autonomy reveals that the majority

Functional autonomy in old age 471

of these studies include either ADL or IADL, or the sum index of both, without

differentiating between elements. With respect to the resource constellation, either physical

or psychological resources are considered. Results are therefore quite contradictory. On the

one hand, cognitive functioning seems to be primarily associated with IADL (Cahn,

Sullivan, Shear, et al., 1998; Steen, Sonn, Borjesson, & Steen, 2001). On the other hand,

positive correlations between cognitive parameters and ADL have only partially been

confirmed. This might be explained by the fact that a considerable amount of studies on

functional autonomy are mostly correlational and cross-sectional, but seldom interdisci-

plinary (mostly either medical or psychological), and mainly based on subjective ratings

rather than on objective ones.

The present study was designed to reduce some of these shortcomings by:

. Describing age- and time-correlated changes of functional autonomy in old age;

. Describing the relation between functional autonomy and health respectively of

functional autonomy and psychological variables;

. Taking into account objective measures as far as possible; and

. Finally, testing the differential and long-term impact of physical and cognitive

resources on ADL and IADL by using structural equation model (SEM) analysis.

In fact, the study of the impact of cognitive and physical resources on various aspects of

functional autonomy requires a differential approach to the resource side as well as to the

competence or outcome side. The rationale of our SEM is based to the two-component

model of everyday competence of Baltes and collaborators (1993, 1996), which

differentiates between a basic level of competence (ADL), and an expanded level of

competence (IADL). In our model, we distinguish between indirect predictors (age) and

proximal predictors (directly related with autonomy such as physical resources such as

mobility or psychological resources such as memory) having an impact on both

components of functional autonomy, that is, ADL and IADL. Our study allows

optimizing the two-component model of Baltes and collaborators by introducing

objectively assessed cognitive and physical resources (memory tests performed on a

computer or muscle strength measured in Watt). We expect that age has little direct

impact on ADL and IADL, but a significant negative impact on both proximal resources,

mobility and especially on memory. Furthermore, and based on existing correlational

data, we expect that mobility and memory have a strong differential impact on functional

autonomy—mobility being the stronger long-term predictor for ADL than memory, and

for IADL the inverse. Indeed, because the IADL are more complex than ADL tasks,

they are also more affected by cognitive functions (Steen et al., 2001; Willis, 1996). On

the other hand, ADL are primarily determined by objective health, especially by a good

physical functioning (Baltes et al., 1993, 1996).

Methods

Participants

This study is part of the Basle Inter-Disciplinary Study on Aging (IDA-Study) with status

measurements in a 2-year interval (Perrig-Chiello, 1997; Perrig-Chiello, Perrig, Stahelin,

Krebs & Ehrsam, 1996).2 The project is a follow-up of a longitudinal study that started in

1960 and collected mostly biomedical data from a large sample of 6,400 healthy persons

472 P. Perrig-Chiello et al.

recruited from an industrial base (the sample is considered representative of the healthy

elderly urban population in Switzerland; Widmer et al., 1981). In the current project, the

Interdisciplinary Study on Aging (IDA), subjects from the original sample have been

recruited if they conformed to two criteria. Firstly, they had to be at least 65 years old and

secondly, they had to live independently (i.e., not in an institution) in the area of Basle.

From 3,768 persons that corresponded to this restriction, 848 persons were randomly

selected and invited to participate in the study. They were informed that they would be

required to travel to the test site, the Geriatric University Clinic of Basle, independently. A

total of 442 persons aged 65 – 94 years (312 males, 132 females, mean age¼ 75) agreed to

participate in the initial wave of the IDA-Study, which took place in 1993 at the Geriatric

University Clinic of Basle. Participants arrived in the morning with an empty stomach.

After blood samples had been drawn, they had a breakfast. Next, a team of physicians

collected the anthropometric and clinical data, and psychometric data were collected by a

team of psychologists; 337 persons (227 men and 107 women) were re-tested in the second

wave 2 years later. A telephone inquiry revealed that the main reasons for attrition were illness

(42%), death (22%) and absence from home/travel in the scheduled test period (16%).

Variables3

Functional autonomy*. To assess functional autonomy we used an adapted version of the

I/ADL scales (Katz, Ford, Moskowitz, Jackson & Jaffe, 1963; Lawton & Brody, 1969;

Perrig-Chiello, 1995), consisting of 11 items with a 3-point scale (1¼ yes, I’m able, 2¼ I’m

partly able, 3¼ I’m not able at all; minimal total score: 11 points¼ absolutely independent;

maximal score: 33 points¼ absolutely dependent). This test was administered in 1993 (T1)

and 1995 (T2). T1 mean (M)¼ 12.1, SD¼ 1.6, Cronbach’s alpha¼ .81; T2 M¼ 19,

SD¼ 2.1; Cronbach’s alpha¼ .76. Factor analysis revealed two factors:

. ADL grouping together the rather basic components of independent living, and

. IADL including more expanded competencies of daily activities:

� Subtest 1: ADL—consisted of six items: climb stairs, washing/bathing, dressing,

pedicure, moving around in own house and the surroundings (T1 M¼ 6.3,

SD¼ 0.7, range¼ 7, Cronbach’s alpha¼ .65; T2 M¼ 6.5, SD¼ 0.8, range¼ 8,

Cronbach’s alpha¼ .61).

� Subtest 2: IADL—consisted of five items: cooking/preparing meals, shopping,

house-keeping, taking care of financial matters, carrying out minor repair work at

home (T1 M¼ 5.2, SD¼ 0.6, range¼ 6, Cronbach’s alpha¼ .69; T2 M¼ 5.6,

SD¼ 0.7 range¼ 7, Cronbach’s alpha¼ .62).

For our analyses, we were primarily interested in the combined measure of functional

autonomy (IADL/ADL). For the SEM analyses, however, we used the two separate

measures in order to get a better appreciation of the differential effects of physical and

cognitive resources.

Physical and psychological resources

. Objective health was assessed only at T1 and was operationalized through 20

parameters. Each parameter was assigned either 0 (¼parameter is in the normal

Functional autonomy in old age 473

range) or 1 (¼parameter is beyond the normal range); the sum was defined as the

‘‘objective health index’’ (M¼ 2.7, SD¼ 1.71, range¼ 9). The indicators were:

� Anthropometric parameters: Systolic and diastolic blood pressure, pulse;

� Serum parameters: cholesterol, iron, blood sugar, ferritin, haemoglobin, MCV

(mean cell volume), HDL (high density lipoprotein), triglycerides, leukocytes,

thrombocytes;

� Electro-cardiogram parameters: rhythm, blocks, ischaemia, necroses, hypertrophy

and digitalis.

. Subjective health* (3-point scale: 3¼ very good, 1¼ very bad health) (T1 M¼ 2.83,

SD¼ 0.43; T2 M¼ 2.7, SD¼ .44; range¼ 2 at both measurements).

. Health complaints*: a list of 11 frequent health complaints (e.g., headaches, stomach/

intestinal complaints, rheumatic pains, heart troubles, respiratory difficulties, etc.) as

well as three open categories was presented to participants (yes/no responses) (T1

M¼ 2, SD¼ 1.29, range¼ 7; T2 M¼ 2.8, SD¼ 1.5, range¼ 8).

. Physical strength legs (mobility)* was measured by a leg extensor power rig (measured in

Watt) (T1 M¼ 15 (7), range¼ 18; T2 M¼ 13 (8) range¼ 19).

. Memory*: A computerized test was used to investigate memory performance. The test,

which allows assessing different memory dimensions and has been used before in

different studies, meets all psychometric requirements (Perrig-Chiello & Perrig, 1995;

Perrig, Perrig-Chiello & Stahelin, 1997). The memory parameters are assessed as

follows:

� Free recall (explicit memory): 20 min after having scanned two almost identical

scenes for missing elements, participants are asked to recall all the missing items

they had detected before (T1 M¼ 9.6, SD¼ 4.03, range¼ 20; T2 M¼ 8.6,

SD¼ 4.52, range¼ 18).

� Perceptual speed (reaction time): As quickly as possible, participants had to identify

and to name pictures on the computer screen, which became progressively clearer

(T1 M¼ 5.62, SD¼ 1.11, range¼ 6.9; T2 M¼ 5.54, SD¼ 1.21, range¼ 7.5).

� Working memory: A picture-naming task, as described above, was repeated with

old pictures and a set of new pictures. At the same time, subjects had to respond

with their left or right index finger to little suns flashing on either the left side or

the right side of the computer screen. The percentage of correct responses was

used for this variable (T1 M¼ 75, SD¼ 22, range¼ 100; T2 M¼ 72, SD¼ 23,

range¼ 100).

. Psychological well-being was assessed by means of a nine-item test, which includes the

following dimensions: satisfaction with own past, purpose of life and mastery (3-point

scale: 1¼ I do not agree to 3¼ I absolutely agree) (range¼ 16). This instrument meets

all psychometric standards (T1 M¼ 23.53, SD¼ 2.74; T2 M¼ 23.32, SD¼ 2.8;

Cronbach’s alpha at both measurements¼ .66 and .68; 3-year-stability: r¼ .60,

p5 .001) (Perrig-Chiello, 1996, 1997).

Analyses

First we analysed the age and time changes of functional autonomy and psychophysical

resources (analyses of variance; ANOVAs). Then, a correlational approach was used to

474 P. Perrig-Chiello et al.

determine the relationship between these variables. Finally, SEM analyses were used to

determine the differential longitudinal predictive power of physical strength and memory on

ADL and IADL (always controlling for age). The analyses were performed with SPSS

(version 9.0) and AMOS (version 4.0).

Results

Age and time-correlated changes in functional autonomy

Results of ANOVAs showed significant main effects for age (F(3,337)¼ 12.19,

p5 .0001) and for time F(1,337)¼ 14.15, p5 .0001) with regard to limitations in

functional autonomy in general (IADL and ADL; Figure 1). No significant interactions

were found. An increase of the limitations in functional autonomy is not only observed

with advancing age (i.e., cross-sectional change for all age groups) but also already within

a 2-year period, especially in the oldest cohort (longitudinal change). At the first

measuring point, 65% of our sample did not show any impairment of autonomy; 2 years

later this was only the case for 51%.

ANOVAs controlling for age, time and gender revealed that women scored significantly

higher in limitations of functional autonomy than men (F(1,337)¼ 4.45, p5 .05) (no

significant interactions). Separate analyses for ADL and IADL showed, however, that this is

only the case for ADL (F(1,337)¼ 37.24, p5 .001) and not for IADL (F(1,337)¼ 0.07,

n.s.). Further ANOVAs controlling for education and marital status did not show any

significant main effects.

Correlates of functional autonomy and their age- and time-related change

Our data show that functional autonomy is positively correlated with subjective

and objective health, muscle strength, memory functions and psychological well-being

(Table I).

Results of ANOVAs show significant main effects for age group and time for most of these

variables, especially for memory variables and muscle strength (Table IIa and b). The only

correlated variable, which did not show any decline, is psychological well-being.

Figure 1. Age- and time-associated increase of dependency in four age groups.

Functional autonomy in old age 475

Longitudinal predictors of ADL and IADL

On the basis of these insights, we were interested in the long-term predictive power of the

age-and time-deteriorating resources of functional autonomy, such as memory (free recall,

working memory, perceptual speed) and physical strength (mobility). In order to test this

SEM analyses were used. Because we expected differential long-term predictive effects of

the two proximal resources physical strength (mobility) and memory on ADL and IADL, we

calculated separate models for both autonomy components. In every model, age was

introduced as a control variable. Memory variables were expected to predict better IADL

and mobility was expected to predict better ADL. To test these hypotheses, we used the chi-

square difference test to compare two models, in which one of the path coefficients is fixed at

zero. In line with the recommended use of the SEM approach (Anderson & Gerbing, 1984),

this test allows inferences on the significance of a specific path based on test results of an

overall model.

In the first step, we tested the long-term impact of memory and mobility measured at the

first wave (T1) on ADL competence 2 years later (ADL-T2). The longitudinal analysis

results with the corresponding fit-indices and results of Dw2 tests for the whole model are

presented in Figure 2. In this test, mobility clearly appears as a significant predictor for

ADL, whereas memory does not. Both proximal resources, mobility and memory, are

significantly related to age—however, in this model, age per se is not a significant predictor

of ADL.

In the second step, we tested the same model, however, with IADL as dependent variable.

Results show that the strongest predictor is now memory, and not mobility. Again, age is not

a significant predictor of IADL (Figure 3).

Discussion

The present study aimed to provide a description of age- and time-related changes of

functional autonomy and the psychophysical resources correlated with these changes. A

central question was to find out how several physical and psychological resources have a

differential long-term predictive power on ADL and IADL. Although our sample was

composed of average healthy elderly, an increase of limitations in functional autonomy was

not only observed with advancing age but already within a 2-year period, this independently

from educational or marital status. This shows that significant losses are to be expected

within and between age groups and that the time factor becomes a crucial variable for

Table I. Correlation between dependency and health and psychological variables (T1).

1 2 3 4 5 6 7 8 9

1. Subjective health 1 .33*** .09 7.13* .13* 7.11 7.19** 7.26*** .12*

2. Health complaints 1 .05 7.19** 7.09 .10 7.11 7.13* .13*

3. Objective health 1 .08 7.03 .02 .01 .04 .14*

4. Psych. well-being 1 .04 7.08 .02 7.02 7.19**

5. Muscle strength legs 1 7.24*** .29*** .33*** 7.25***

6. Reaction time/speed 1 7.37*** 7.32*** .23**

7. Free recall 1 .36*** 7.19**

8. Working memory 1 7.32**

9. Dependency 1

*p5 .01; **p5 .001; ***p5 .0001.

476 P. Perrig-Chiello et al.

Tab

leII

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70

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4ye

ars

75

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04

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s

T1

T2

T1

T2

T1

T2

T1

T2

Ob

ject

ive

hea

lth

2.3

(1.4

1)

2.5

(1.7

5)

2.7

(1.7

8)

3.3

(1.9

)

Su

bje

ctiv

eh

ealt

h2

.88

(0.3

3)

2.9

5(0

.22)

2.8

8(0

.36

)2

.77

(0.5

2)

2.7

7(0

.47

)2

.75

(0.4

8)

2.8

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.67

(0.5

7)

Hea

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com

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1.0

9(1

.26

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1.2

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(1.3

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2.6

(1.4

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3.1

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3.1

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3.1

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)

Mu

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17

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6)

17

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16

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(6.2

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14

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13

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23

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23

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73

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62

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(26.0

6)

Functional autonomy in old age 477

preventive measures. Furthermore, our data revealed significant gender differences: even

though women show significantly higher dependency in ADL than men, they do not differ in

IADL. Women’s higher dependency in ADL may be a consequence of the gender

differences in objective and subjective health during the life-span observed in various other

studies on the one hand, and significantly lower muscle strength on the other hand.

Although women live longer and invest more in their health, they show a significantly higher

morbidity and dependency rate than men (Verbrugge, 1989; Rahman, Strauss, Gertler,

Ashley, & Fox, 1994; Drever, Doran, & Whitehead, 2004). The fact that the women in our

study do not differ in IADL might indicate that they have to continue functioning in every

day life despite possible health impairments (in contrast to old men, old women are more

likely to live alone, which is also the case in our study).

Furthermore, our data show that functional autonomy is positively correlated with a series

of health variables (subjective and objective health, muscle strength) and memory functions

as well as with psychological well-being. With the exception of psychological well-being, all

these measures show an age- and time-correlated decrease. These results clearly

demonstrate imperatives and limitations of possible preventive interventions. On the one

hand, improving the age- and time-deteriorating resources such as muscle strength and

memory might be a meaningful goal of prevention attempts. On the other hand, age- and

time-resistant measures such as psychological well-being need to be considered differently,

in the sense that they may be more resistant to modification. As has been shown,

psychological well-being can be considered indeed as a rather stable personality trait

(Kozma et al., 1991), but also as a powerful prerequisite of functional autonomy in old age.

Table IIb. Age and time changes in health and psychological variables.

df F p

Objective health

Age 3,392 2.38 5.05

Time – – –

Subjective health

Age 3,434 2.29 5.05

Time 1,341 2.74 .10

Health complaints

Age 3,341 3.30 .02

Time 1,341 146.22 .001

Muscle strength legs

Age 3,320 23.91 5.0001

Time 1,320 18.64 5.0001

Psychological well-being

Age 3,341 0.96 n.s.

Time 1,341 1.87 n.s.

Reaction Time

Age 3,338 11.13 5.0001

Time 1,338 8.91 5.0001

Free recall

Age 3,337 28.77 5.0001

Time 1,337 29.35 5.0001

Working memory

Age 3,332 27.54 5.0001

Time 1,332 6.21 .01

478 P. Perrig-Chiello et al.

Finally, the SEM analyses allowed testing of differential long-term effects of resources,

memory and physical strength for ADL and IADL. Age per se is not significant, but has a

strong indirect impact on ADL and IADL. The strongest direct predictors are physical

strength for ADL and memory, and physical strength for IADL. Both predictors are strongly

related to age—indicating the age-correlated decrease of these resources.

With regard to the practical implementation of our results, this means that even though

individual differences exist in respect to the age-correlated decrease of physical strength and

memory, training programmes to prevent losses as well as to maintain and foster the existing

resources can and should be promoted. As shown in experimental intervention studies, both

physical strength as well as memory can be modified successfully (Oswald et al., 1996;

Perrig-Chiello, Perrig, Ehrsam, & Stahelin, 1998). A promising step in this direction is an

Figure 2. Long-term predictors of activities of daily living (ADL).

Functional autonomy in old age 479

intervention programme for resistance training that has been carried out in our study

programme (IDA-Study), it showed positive direct effects on muscle strength, but also

positive indirect effects on memory and well-being (Perrig-Chiello et al., 1998).

Our study adds some strong evidence that psychological factors have an important impact

on functional autonomy, especially on IADL, in old age. Part of the challenge of preventing

unnecessary dependency in old age should therefore be (a) to take into account the large

differences in availability, utilization and interaction of old people’s physical and

psychological resources and (b) to recognize the large diversity among the elderly—age

per se is not the best predictor for autonomy.

Acknowledgements

This study was supported by the Swiss National Science Foundation (Study-Nr. 4032-

035642).

Figure 3. Long-term predictors of instrumental activities of daily living (IADL).

480 P. Perrig-Chiello et al.

Notes

1. In the year 2000, this was the case for 80% of the people aged 80 – 85 in Switzerland , and

for 65 – 70% of people 85 and over (Hopflinger & Hugentobler, 2003).

2. This study has been approved by the ethic committee of the University Hospital of Basel.

3. All variables with a * were measured in both waves.

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