The Gerontologist
Vol. 49, No. S1, S100–S107
doi:10.1093/geront/gnp075
Published by Oxford University Press on behalf of The Gerontological Society of America 2009.
The Prescribed Amount of Physical Activity in
Randomized Clinical Trials in Older Adults
Judy Kruger, PhD,1,2 David M. Buchner, MD,2 and Thomas R. Prohaska, PhD3
Purpose: Over the past two decades, a consensus
has formed that increasing physical activity and reducing sedentary behavior in older adults are important for physical and cognitive health. Although there
is strong evidence that regular physical activity can
prevent or delay the onset of many chronic diseases,
a major concern is ensuring that older adults take
part in adequate levels of physical activity. Design
and Methods: This article describes the amount
of physical activity prescribed between 1980 and
2005 to sedentary older adults enrolled in randomized controlled trials (RCTs) using MEDLINE, Health
and Psychological Instruments, EBM Reviews, CINAHL, ERIC, PsychInfo, and Social Science Abstracts
with the key words “exercise,” “physical activity,”
and “older adult.” More than 13,502 research abstracts were reviewed, and 160 RCTs 12 weeks or
more in duration with documented outcomes of physical activity were synthesized. Results: The average prescribed dose of aerobic activity provided by
interventions for older adults was less than the recommended amount of 150 min or more per week of
moderate-intensity physical activity. In interpreting the
results of RCTs, there is an insufficient body of evidence on the relationship between physical activity
and cognitive health. However, studies indicated that
moderate-intensity physical activity had a positive effect on cognitive health. Implications: Given the
broad consensus of a dose–response relationship
between aerobic activity and a variety of health
outcomes, the RCT literature appears to have underestimated the benefit of physical activity for previously
1
Address correspondence to Judy Kruger, PhD, Division of Nutrition,
Physical Activity, and Obesity, Centers for Disease Control and Prevention, 4770 Buford Highway Northeast, K-46, Atlanta, GA 30341-3717.
E-mail: [email protected]
2
Physical Activity and Health Branch, Division of Nutrition, Physical
Activity, and Obesity, National Center for Chronic Disease Prevention
and Health Promotion, Centers for Disease Control and Prevention,
Atlanta, Georgia.
3
Department of Community Health Sciences, School of Public Health,
University of Illinois at Chicago.
sedentary older adults because the prescribed dosages are not consistent with those recommended.
Key Words: Physical fitness, Exercise,
promotion, RCT, Cognitive function
Health
Regular physical activity provides substantial
health benefits for older adults, which include reducing the risk for premature mortality from several common chronic diseases (i.e., cardiovascular
disease and colon cancer) and lowering the incidence of functional limitations such as impaired
walking (Keysor, 2003; U.S. Department of Health
and Human Services [USDHHS], 1996). Physical
activity also provides therapeutic benefits, and it is
recommended as part of treatment regimens for
such diseases as hypertension (American College
of Sports Medicine [ACSM] Position Stand, 2004)
and arthritis (American Geriatric Society, 2001).
More recently, bouts of aerobic fitness training have
been shown to improve cognitive function among
sedentary older adults (Colcombe & Kramer,
2003). In spite of accumulating evidence that physical activity can delay the onset of many chronic
conditions seen in adulthood, research has not advanced sufficiently to make specific recommendations to prevent Alzheimer’s disease and related
disorders (Prohaska & Peters, 2007). However,
recommendations related to physical activity are
numerous, and have shifted their emphasis over
the past 30 years from exercise guidelines for clinical practice (ACSM, 1978; American Heart Association [AHA], 1972, 1975) to the premise that
moderate-intensity physical activity can improve
overall health and lower the risk for disease (USDHHS, 1996, 2008). Given the aging of the U.S.
population, it is of particular interest whether the
average dose prescribed in randomized controlled
trials (RCTs) is similar to the minimum amount of
physical activity set forth in recommendations.
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During the 1970s, the AHA published two separate reports that suggested that higher levels of
exercise training (i.e., an intensity of training
equivalent to 60%–90% of maximum heart rate
[HRmax]) would result in higher levels of physical
fitness (ACSM, 1978). These first set of exercise
recommendations (AHA, 1972, 1975), in addition
to the ACSM (1978) recommendations, led to the
development of the “exercise prescription” formula. This formula has been used by exercise specialists, physicians, and health care professionals in
clinical practice to promote physical activity in
terms of frequency, duration, intensity, and type of
exercise. However, in the late 1980s and early
1990s due to findings from laboratory- and
population-based scientific studies, physical activity
recommendations shifted away from the emphasis
on physical performance. In 1995, the Centers for
Disease Control and Prevention (CDC) and the
ACSM developed physical activity recommendations for public health that encouraged every adult
to accumulate 30 min or more of moderate-intensity
physical activity on most, preferably all, days of
the week (corresponding to 5 or more days per
week; Pate et al., 1995).
Since the 1995 CDC/ACSM report was developed, it was commonly thought that moderateintensity physical activity less than 3 days per week,
or less than 30 min per occasion, was considered
insufficient to obtain health benefits. However, although the duration (30 min) was clear in this recommendation, the frequency (i.e., prescribed
number of days) was vague and raised the question
about whether most days of the week meant 4 or 5
days. Recently, after a comprehensive review of
the physical activity literature, the USDHHS published the 2008 Physical Activity Guidelines for
Americans, which stated that for substantial health
benefits, older adults should participate in moderate-intensity physical activity of at least 150 min
per week, in vigorous-intensity physical activity of
at least 75 min a week, or in an equivalent combination of moderate- or vigorous-intensity physical
activities; and the activity should be spread
throughout the week (USDHHS, 2008). The 2008
guidelines also suggested that additional health
benefits could be gained through greater amounts
of physical activity; however, the recommendation
of more than or equal to 150 min of moderateintensity activity was meant as a minimum amount
of physical activity for health benefits and that older adults should be as physically active as their
abilities and conditions allow.
Vol. 49, No. S1, 2009
The RCT literature provides useful information
on the impact of increasing the percentage of adults
who meet these recommendations, in addition to
the feasibility and risks of routinely recommending
high volumes of physical activity to previously sedentary older adults. Because the RCT design provides the strongest evidence of whether an activity
provides health benefits, understanding how the
RCT literature on physical activity in older adults
has evolved is of considerable interest. Moreover,
because the benefits of activity depend upon the
dose, the prescribed dose greatly influences the size
of health benefits reported by RCTs. The purpose
of this article was to systematically review the literature on aerobic physical activity prescribed to
previously sedentary older adults enrolled in RCTs.
The objectives are to review prescription patterns
of RCTs relative to physical activity recommendations for public health, to quantify discrepancies,
and to characterize the dose of activity prescribed
in RCTs with measures of cognitive function.
Methods
The Evidence Based Exercise and Older Adult
(EBEOA) database archives published research on
physical activity interventions among communitydwelling adults (M age ≥60 years) with documented health outcomes. Detailed methods of the design
and conceptual model of the EBEOA database are
described elsewhere (Hong, Hughes, & Prohaska,
2008). Figure 1 briefly describes the overall search
and selection strategy used in this article. A literature search was performed using Medline, Health
and Psychosocial Instruments, EBM Reviews, CINAHL, ERIC, PsychInfo, and Social Science Abstracts from January 1980 to January 2000 using
the key words “exercise,” “physical activity,” and
“older adult,” and a request for English-language
articles. Because the main outcome of interest was
physical activity, abstracts and papers were excluded if they reported only a single bout of exercise, exercise stress/tolerance tests, pharmaceutical
studies (i.e., testing the effects of a drug), or specific therapeutic exercise (i.e., inspiratory muscle
testing), or those without documented physical activity outcomes. To obtain articles published from
January 2000 to December 2005, the same criteria
used to collect articles in the EBEOA database
were applied.
After a full review of the papers, 13,260 were
excluded because (a) the mean age was less than 60
years, (b) the participants included were persons
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Search strategy
1. Inclusion / exclusion
criteria for abstracts
English-language articles using keywords:
‘exercise’ ‘physical activity’ ‘older adult’
12,312 / 1,190
EBEOA citations / Updated citations
Excluded 9,978 / 610
EBEOA citations / Updated citations
2. Inclusion / exclusion
criteria for papers
2,334 / 800
EBEOA citations / Updated citations
Excluded 2,112 / 525
EBEOA citations / Updated citations
3. RCT papers with
aerobic physical activity
222 / 275
EBEOA citations / Updated citations
Excluded 102 / 153
EBEOA citations / Updated citations
4. Aerobic papers of
moderate-intensity with
frequency and duration
120 / 122
EBEOA citations / Updated citations
Excluded 48 / 34
EBEOA citations / Updated citations
5. Aerobic interventions 12
weeks with documented
outcomes
72 / 88
EBEOA citations / Updated citations
Figure 1. Data selection strategy.
younger than 60 years and there were no subanalyses by age, (c) there was no comparison group,
(d) the exposure to physical activity was not well
reported, or (e) the studies were not RCTs.
Although this database included multiple physical
activity intervention design components such as
strength training, flexibility, and balance, for this
synthesis, only RCTs with an aerobic physical activity component and documented outcomes (i.e.,
frequency, duration, intensity) were selected.
Moreover, only aerobic RCTs of 12 weeks or more
in duration were examined as the literature suggests that physical activity interventions of less
than 3 months may not be sufficient to produce
measurable health benefits (Colcombe & Kramer,
2003; Jorgensen, 1995).
Specific outcomes for aerobic physical activity
were the prescribed number of days per week (frequency), the number of minutes per exercise session (duration), and the targeted level of physical
exertion (intensity). Categories of intensity (i.e.,
HRmax, peak oxygen uptake [VO2max], and ratings
of perceived exertion [RPEs]) were adapted using
the ACSM (1993) guidelines. For example, moderate intensity consisted of activities at 60%–79% of
HRmax, at 50%–74% of VO2max, or at an RPE of
12–13.
The average dose of physical activity prescribed
in RCTs was examined by the year published, by
characteristics of the older adult sample (i.e.,
healthy, with an existing chronic diseases, or frail),
and by the inclusion of a measure of cognitive
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Table 1. Distribution of Randomized Clinical Trial Studies on Aerobic Activity of Moderate Intensitya Lasting 12 Weeks or
More (n = 160) Among Adults (≥60 years)
≥150 min/week
<150 min/week
Years
<30 min, <3 days, n (%)
≥30 min, 3–4 days, n (%)
≥30 min, ≥5 days, n (%)
≤1996
>1997
Total
11 (22)
39 (78)
50
30 (32.6)
62 (67.4)
92
5 (27.8)
13 (72.2)
18
Note: aStudies on moderate-intensity activity had older adults training at a maximum heart rate of 60%–79%, a peak oxygen
uptake at 50%–74%, or a rating of perceived exertion of 12–13.
function. Because the CDC/ACSM recommendations (Pate et al., 1995), and the surgeon general’s
report (USDHHS, 1996), recognize that substantial health benefits result from a moderate amount
of physical activity—in the range starting at 30
min or more on most days of the week—RCTs
published prior to 1996 were compared with those
published after 1996. Studies published in 1996
were included in the pre-1996 studies, as it is likely
that recommended levels were adopted and published within the same year. For this synthesis, the
final sample was 160 intervention studies that were
conducted 12 weeks or more in duration and that
prescribed moderate-intensity physical activity.
Results
Between 1980 and 2005, there was a steady increase in the number of aerobic studies targeting
previously sedentary older adults. Table 1 presents
evidence from moderate-intensity interventions 12
weeks or more in duration, with sufficient informa-
tion on the frequency and duration of physical activity to categorize studies. Among the 160 RCTs,
only 18 prescribed 150 min or more of moderateintensity physical activity, and most were published
since 1997. The majority of the studies prescribed
moderate-intensity physical less than 150 min in
varying combinations to older adults.
Table 2 shows the distribution of moderateintensity RCTs by health status of the sample.
Among moderate-intensity RCTs lasting 12 weeks
or more, 93 selected healthy older adults, 56 those
with chronic disease, and 11 those who were frail
as study participants. Since 1997, there has been
an increase in the number of studies that published
results using older adults with chronic disease (e.g.,
cardiovascular disease, chronic lung disease, and
arthritis) as the sample population. The majority
of these studies prescribed less than 150 min per
week of moderate-intensity activity. Of the 160
RCTs, none of the trials trained frail older adults
at recommended levels of physical activity (150
min or more per week).
Table 2. Distribution of Year and Moderate-Intensitya Physical Activity Randomized Controlled Studies Lasting 12 Weeks or
More Among Adults (≥60 years) by Characteristics of Sample (n = 160)
Health status
b
Healthy , n (%)
Chronic diseasec, n (%)
Fraild, n (%)
30 (32.3)
63 (67.7)
10 (17.9)
46 (82.1)
6 (54.5)
5 (45.5)
27 (29.0)
55 (59.2)
20 (35.7)
29 (51.8)
3 (27.3)
8 (72.7)
11 (11.8)
93
7 (12.5)
56
0 (0.0)
11
Years
≤1996
>1997
<150 min/week
<30 min, <3 days
≥30 min, 3–4 days
≥150 min/week
≥30 min, ≥5 days
Total
Notes: aStudies on moderate-intensity activity had older adults training at a maximum heart rate of 60%–79%, a peak oxygen
uptake at 50%–74%, or a rating of perceived exertion of 12–13.
b
Sample selected based on being free of health problems and/or not selected based on the presence of a chronic illness.
c
Sample selected because of chronic disease of interest (e.g., arthritis, coronary heart disease, chronic obstructive pulmonary
disorder).
d
Intervention study described sample as frail in the Methods section.
Vol. 49, No. S1, 2009
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In recent years, there has been an increase in the
number of RCTs that measure cognitive health
outcomes. The present study found that only 4
studies examined cognitive outcomes in 1996,
compared with 18 studies published in 1997 and
beyond (Table 3). Among the studies that examined mental health outcomes, only three studies
prescribed 150 min or more per week of moderateintensity activity. Almost all the 22 interventions
in the sample were delivered three times per week,
and in most cases, exercise sessions lasted at least
30 min. Of the interventions that were at least 12
weeks or more in duration, the most common cognitive health outcome used was the 36-item Short
Form, mental health component.
Discussion
Public health recommendations have shifted
away from a prescribed intensity to meeting a minimum recommended amount of aerobic activity
that is spread throughout the week. The recommendations (ACSM, 1978; AHA, 1972, 1975)
published in the 1970s were clinically oriented and
recommended a much higher dose of physical activity (a duration of 15–60 min, a frequency of 3–5
days, an intensity of 60%–90% of HRmax) than
the recommendations published in mid-1990s. The
later recommendations consisted of physical activity levels of a less intense dose and placed greater
emphasis on the health benefits (Pate et al., 1995;
USDHHS, 1996). Conclusions from the present
study suggest that RCTs typically prescribe less
than the minimum levels of physical activity specified in public health recommendations.
There are several plausible reasons as to why
RCTs tend to prescribe lower amounts of physical
activity than are recommended. Presumably, the
prescribed frequency of 5 days rather than 3–4 days
of activity may be more expensive and more difficult (because they require longer staff hours to administer trial procedures), and a study must simply
be able to say that the dose of activity it has prescribed could plausibly result in the effects of interest—it does not necessarily need to relate the dose
to a public health recommendation. Moreover, it is
reasonable to demonstrate first that an effect exists,
before endorsing dose–response studies. Finally,
concerns over possible adverse events and the possibility of high attrition with a more rigorous program may also contribute to the lower prescribed
volumes of physical activity. Although it was
not the purpose of this article to track dose-related
negative outcomes, this synthesis found that the
frequency of falls or sprains among older adults enrolled in moderate-intensity RCTs was low. Future
studies may also need to consider utilizing prescriptions that reflect the 2008 guidelines, for example,
combining 3 days of moderate-intensity activity
with 2 days of vigorous-intensity activity and prescribing higher durations of activity per occasion to
determine negative outcomes. To date, there is little
existing scientific evidence to determine whether
health benefits of 30 min on 5 days a week are any
different from the health benefits of 50 min on 3
days a week. However, one 10-week study by Stiggelbout, Popkema, Hopman-Rock, de Greef, and
van Mechelen (2004) that prescribed 35 min of
light aerobic activity to older adults had different
outcomes if performed once or twice a week. Another study, by Wadell, Henriksson-Larsen, Lundgren, and Sundelin (2005), also found reduced
health benefits due to different lengths of training
times (1 vs. 3 days a week).
The increase in the number of RCTs since 1997
targeting cognitive function is suggestive of a positive trend, although more research studies that
document the frequency, duration, intensity, and
type of activity are needed to guide future public
health recommendations for cognitive impairment.
This study found that the average dose prescribed
in RCTs with measured outcomes of cognitive
function was less than the 150 min per week recommendation. The optimal training frequency for improving or maintaining cognitive health is not
known (Robertson, Campbell, Gardner, & Devlin,
2002), although the 2008 guidelines suggest that
regular physical activity reduces the risk for many
adverse health outcomes such as depression and
cognitive function (USDHHS, 2008). In a metaanalysis by Colcombe and Kramer (2003), aerobic
fitness training of 30 min or less had little impact
on cognitive function. This finding is congruent
with the 2008 guidelines that are not focused on
frequency (days per week), but they do state that
the more activity individuals do, the more health
benefits they gain. There is a need for more research measuring cognitive health outcomes, as
the literature still remains controversial as to the
quantification of the exact amount of physical activity needed for health benefits.
Several limitations of this study should be considered. First, this article focused on the aerobic component of prescribed physical activity, and many
studies do not adequately describe the types of activities with enough specificity to allow comparison.
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Vol. 49, No. S1, 2009
S105
316; 24
101; 12
53; 12
134; 24
43; 12
187; 48
Rejeski (2002)
Stahle (1999)
Tsai (2002)
Van Gool (2005)
Wadell (2005)
Williams (1997)
Group 1:2:5:6
Group 1:2
Group 1:2
Group 1:2:5:6
Group 1:2
Group 1:2
Group 1:4
Group 1:2:3
Group 1:4:6
Group 1:2:6
Group 1:2:4
Group 1:2
Group 1:2
Group 1:6
Group 1:2
Group 1:2
Group 1:6
Group 1:6
Group 1:2
Group 1:2:3
Group 1:2:5
Group 1:2
Types of exercise
interventiona
3; 30
3; 50
3; 30
3; 30
3; 45
2; 35
3; 45
3; 40
3; 30
3; 45
3; 50
3; 25
3; 30
3; 40
3; 30
3; 30
3; 30
3; 60
20 visits or 2
days a week; 23
3; 45
3; 35
3; 60
Frequency (days per week);
duration (minutes per occasion)
SF-36 MC
KQ
SF-36 MC
SF-36 MC
SF-36 MC
DASS
GDS
CES-D
AIMS
EFI
CES-D
SF-36 MC
CES-D
CES-D
SF-36 MC
GDS
QLP
QLP
SF-12 MC
GDS
BDI
GDS
Cognitive health
outcomeb
Significant difference BG (p < .05); significant
difference WG (p < .05)
Significant difference BG (p < .05); significant
difference WG (p < .05)
No difference BG; significant difference WG (p < .05)
Significant difference BG (p < .05); Significant
difference WG (p < .05)
No difference BG; no difference WG
No difference BG; significant difference WG (p < .05)
No difference BG; no difference WG
Significant difference WG (p < .01)
Significant difference BG (p < .05); no difference WG
No difference BG; no difference WG
Significant difference BG (p < .05); significant
difference WG (p < .05)
Significant difference BG (p < .05); significant
difference WG (p < .05)
No difference BG; significant difference WG (p < .05)
No difference BG
No difference WG
Significant difference WG (p < .05)
No difference BG; no difference WG
Significant difference BG (p < .05)
Significant difference WG (p < .04)
Significant difference WG (p < .01)
No difference BG; significant difference WG (p < .05)
Significant difference BG (p < .05)
Effect of aerobic exercise on cognitive health outcome
(between groups [BG] and within groups [WG])
b
Notes: aTypes of exercise interventions: (1) aerobic; (2) control; (3) strength (or resistance) exercise; (4) flexibility exercise; (5) diet; and (6) others.
Cognitive health measure: GDS = Geriatric Depression Scale; BDI = Beck Depression Inventory; CES-D = Center for Epidemiological Studies–Depression scale; SF-36
MC = 36-item Short Form, mental health component; QLP = quality-of-life parameters, mental health; SF-12 MC = 12-item Short Form, mental health component;
EFI = Exercise-Induced Feeling Inventory, positive engagement; AIMS = Arthritis Impact Measurement Scale, depression component; KQ = Karolinska Questionnaire, depression;
DASS = Depression Anxiety Stress Scale.
174; 24
438; 12
Motl (2005)
Penninx (2002)
55; 12
Matsouka (2005)
120; 12
101; 16
31; 12
48; 12
40; 12
64; 24
32; 12
52; 12
283; 12
108; 16
33; 12
Blumenthal (1991)
Collins (2004)
Emery (1990)
Etnier (2001)
Gardner (2005)
Gary (2004)
Lavie (1997)
Lavie (1996)
Li (2005)
Mangione (2005)
Minor (1989)
134; 16
46; 24
N; duration
(weeks)
Blumenthal (2005)
Antunes (2005)
First author (year)
Table 3. Summary of Moderate-Intensity Physical Activity Intervention Studies With Cognitive Health Outcomes
A proportion of the studies were multicomponent
(i.e., included strength training, flexibility, and balance components); thus, it is possible that the focus
on the volume of aerobic activity may have underestimated the amount of physical activity performed
by older adults. Second, it was not possible to account for the fact that participants in exercise trials
begin at a lower dose and gradually increase it, until
they reach the prescribed level. Third, information
on the adherence rate to the prescribed volume or
on the number or percentage of participants who
completed each trial was not synthesized in this
study. However, Hong and coworkers (2008) analyzed findings from the EBEOA database and found
that group-based exercisers had higher attendance
rates than those who exercised individually. Fourth,
some studies included in this synthesis occurred before the development of physical activity recommendations. Finally, not all RCTs provided basic
demographic characteristics such as sex, age range,
race/ethnicity, or education, which limits our ability
to make reference to specific groups of older adults.
In summary, this article provides an overview of
the gap between the number of published studies
prescribing aerobic-based physical activity and the
recommended guidelines for physical activity and
public health. Based on the findings of this investigation, relatively few studies prescribed 150 min
or more per week of moderate-intensity physical
activity, including those studies that measure cognitive function outcomes. These gaps relate to the
ability of the literature to inform public health recommendations and characterize the benefits of
higher volumes of physical activity. Thus, most
RCTs of aerobic activity in older adults prescribed
less than the recommended amount of physical activity, and future research should seek to fill these
gaps.
Funding
This publication was funded by the CDC Special Interest Project #13
(U48/CCU509661), which focused on evidence-based outcomes of exercise in older adults (1999–2002). The contents of this article are solely the
responsibility of the authors and do not necessarily represent the official
position of the CDC.
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Received June 23, 2008
Accepted November 14, 2008
Decision Editor: Angela K. Hochhalter, PhD
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