Characteristics of Physical Activities in Daily Life
in Chronic Obstructive Pulmonary Disease
Fabio Pitta, Thierry Troosters, Martijn A. Spruit, Vanessa S. Probst, Marc Decramer, and Rik Gosselink
Respiratory Rehabilitation and Respiratory Division, University Hospitals, and Department of Rehabilitation Sciences, Faculty of Kinesiology
and Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium; Department of Physiotherapy,
Universidade Estadual de Londrina, Londrina, Brazil
Quantification of physical activities in daily life in patients with
chronic obstructive pulmonary disease has increasing clinical interest. However, detailed comparison with healthy subjects is not available. Furthermore, it is unknown whether time spent actively during
daily life is related to lung function, muscle force, or maximal and
functional exercise capacity. We assessed physical activities and
movement intensity with the DynaPort activity monitor in 50 patients (age 64 ⫾ 7 years; FEV1 43 ⫾ 18% predicted) and 25 healthy
elderly individuals (age 66 ⫾ 5 years). Patients showed lower walking time (44 ⫾ 26 vs. 81 ⫾ 26 minutes/day), standing time (191 ⫾
99 vs. 295 ⫾ 109 minutes/day), and movement intensity during
walking (1.8 ⫾ 0.3 vs. 2.4 ⫾ 0.5 m/second2; p ⬍ 0.0001 for all), as
well as higher sitting time (374 ⫾ 139 vs. 306 ⫾ 108 minutes/day;
p ⫽ 0.04) and lying time (87 ⫾ 97 vs. 29 ⫾ 33 minutes/day; p ⫽
0.004). Walking time was highly correlated with the 6-minute walking test (r ⫽ 0.76, p ⬍ 0.0001) and more modestly to maximal
exercise capacity, lung function, and muscle force (0.28 ⬍ r ⬍ 0.64,
p ⬍ 0.05). Patients with chronic obstructive pulmonary disease are
markedly inactive in daily life. Functional exercise capacity is the
strongest correlate of physical activities in daily life.
Keywords: controlled study; chronic obstructive pulmonary disease;
correlates; DynaPort; triaxial accelerometer
Guidelines recommend that, for people of all ages, a minimum
of 30 minutes of daily physical activity of moderate intensity,
such as walking, is necessary to maintain or develop fitness (1).
Those not meeting this standard are considered insufficiently
active. In addition, the level of disability and deconditioning is
a strong predictor of mortality (2–4), and adherence to current
physical activity guidelines is associated with significant reduction in risk of all-cause mortality (5). Therefore, quantifying
physical activities in daily life is of great value, especially in
sedentary populations, and the time spent actively during daily
life, together with intensity and frequency, are key issues in the
analysis of a population’s usual physical activity level (6).
Patients with chronic obstructive pulmonary disease (COPD)
frequently report dyspnea related to everyday tasks (7, 8). Therefore, it has been suggested that patients with COPD may be in
a downward spiral of symptom-induced inactivity (9), leading
to deconditioning and muscle weakness. However, objective
comparison between patients with COPD and age-matched
healthy control subjects concerning time spent actively in daily
life and intensity of movements is currently lacking. This comparison is crucial to judge the real impact of the disease on usual
activities.
Recently, we validated a triaxial accelerometer in patients
with COPD (DynaPort Activity Monitor; McRoberts BV, The
Hague, Netherlands) (10), which is able to quantify precisely
the time spent on different activities (walking, cycling) and body
positions (standing, sitting, lying) in daily life, as well as movement intensity during walking. The use of this tool provides
detailed and accurate comparison of physical activities in daily
life between patients with COPD and healthy elderly control
subjects.
Assessment of physical activities in daily life also enables one
to investigate the relation between usual physical activity level
and its potential physiologic surrogates. In patients with COPD,
only modest relations have been found between laboratorybased exercise tests and lung function impairment (11). However, it is unclear to what extent objectively measured activities
in real life are correlated with lung function, muscle force, or
laboratory-based exercise tests.
Therefore, the present study was designed to investigate physical activities in daily life in patients with COPD compared with
healthy age-matched individuals. In addition, we studied the
relationship between physiologic variables and physical activities
in daily life in patients with COPD. Preliminary results of this
study have been previously reported in the form of abstracts
(12, 13).
METHODS
Design
Physical activities in daily life, pulmonary function, respiratory and
peripheral muscle force, maximal exercise capacity, and a 6-minute
walking distance (6MWD) test were assessed in patients with COPD
and healthy elderly subjects and cross-sectionally compared.
Subjects
(Received in original form July 3, 2004; accepted in final form January 18, 2005)
Supported by CAPES/Brasil (F.P.). T.T. is a postdoctoral fellow of the FWOVlaanderen. M.A.S. is a postdoctoral fellow at KU Leuven (PDM/04/230). This
study is partially funded by FWO-Vlaanderen grants Levenslijn 7.0007.00, G.0237.01,
and Foundation Van Goethem-Brichant, 2001.
Correspondence and requests for reprints should be addressed to Rik Gosselink,
Ph.D., P.T., Respiratory Rehabilitation and Respiratory Division, University Hospital
Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium. E-mail: rik.gosselink@uz.
kuleuven.ac.be
This article has an online supplement, which is accessible from this issue’s table
of contents at www.atsjournals.org
Am J Respir Crit Care Med Vol 171. pp 972–977, 2005
Originally Published in Press as DOI: 10.1164/rccm.200407-855OC on January 21, 2005
Internet address: www.atsjournals.org
Sixty-two patients (46 men) suffering from mild to very severe COPD
(Global Initiative for Chronic Obstructive Lung Disease [GOLD]
classes I–IV) (14) were initially included. They were all retired or on
sick leave and no longer employed. Inclusion criteria were as follows:
(1 ) stable condition at inclusion, with no infection or exacerbation for
at least 3 months; (2 ) absence of severe and/or unstable cardiac disease
as shown by electrocardiogram during rest and maximal exercise test;
and (3 ) absence of other pathologic conditions that could impair physical activities in daily life (e.g., cerebrovascular diseases and rheumatism
[see Presence of Comorbidities in Methods]).
The control group included 26 healthy age- and sex-matched subjects
(17 men), all of them retired. Twenty-four of them were relatives of
employees or students of the hospital and two were healthy spouses of
patients included in the COPD group. Inclusion criteria were the same
as the COPD group, with the addition of normal spirometry results.
None of the individuals from both groups was engaged in any exer-
Pitta, Troosters, Spruit, et al.: Physical Activities in Patients with COPD
973
cise-training program before taking part in the study. All individuals
gave informed consent, and all procedures were done according to the
research ethics of the Declaration of Helsinki (15).
(4%) were using oral corticosteroids (␹2 9.02, p ⫽ 0.003). The mean
dose was 8 ⫾ 7 mg/day in these 18 patients with COPD. The healthy
subject was using oral corticosteroids because of a scar inflammation
after an abdominal plastic surgery which happened 3 months before
inclusion in the study. The dose was 4 mg/day and the inflammatory
treatment was in its last week, after complete remission of the postoperative complication.
Exclusions
Twelve patients with COPD and one healthy elderly subject were excluded from the statistical analysis because they were not able to provide
2 valid days of assessment, which was considered the minimum number
of necessary days to assess reliably physical activities in daily life (see
Assessment of Physical Activity Level in Daily Life in Methods).
A valid day of assessment was defined as 12 hours of measurement
with the device correctly positioned and without any technical defect.
All excluded subjects had a maximum of 1 assessment day considered
valid. The reasons for invalid assessments were as follows: misplacement
of the device (in seven patients with COPD) and technical problems
(i.e., interruption of the measurement because of lack of battery power
in five patients with COPD and one healthy subject). Therefore, statistical analysis was performed with 50 patients with COPD and 25 healthy
elderly subjects (Table 1). The 12 excluded patients with COPD were
not different from the remaining 50 in terms of lung function, muscle
force, and exercise capacity. More detail on the exclusions is provided
in the online supplement.
Presence of Comorbidities
A detailed overview of comorbidities in both groups is shown in Table
2. Both groups had similar prevalence of high blood pressure, back
pain, arthritis, and obesity. The prevalence of osteoporosis, depression,
and stable heart disease was higher in patients with COPD, as previously
shown in the literature (16–18). In addition, matching for cardiac conditions could be checked based on the results of the maximal cycling
exercise test. During this test, no electrocardiographic abnormalities or
clinical signs suggestive of severe cardiac disease that could impair the
performance of usual physical activities were detected in any subject
from both groups. Matching for smoking status was obviously not possible, because COPD is a disease linked to smoking, and the prevalence
is lower in the general population.
Eighteen patients with COPD (36%) and only one healthy subject
TABLE 1. BASELINE CHARACTERISTICS
Age, yr
Sex, male/female
BMI, kg/m2
Pulmonary function
FEV1, %pred
FVC, %pred
FRC, %pred
TLC, %pred
TL,CO, %pred
Muscle function
QF, %pred
HF, %pred
PImax, %pred
PEmax, %pred
Exercise capacity
6MWD, %pred
Wmax, %pred
Peak V̇O2, %pred
Patients with
COPD (n ⫽ 50)
Healthy Elderly
Subjects (n ⫽ 25)
64 ⫾ 7
36/14
25 ⫾ 6
66 ⫾ 5
17/8
26 ⫾ 3
43
87
155
114
49
⫾
⫾
⫾
⫾
⫾
18
22
39
20
19
111
118
108
107
93
⫾
⫾
⫾
⫾
⫾
20*
19*
20*
13
12*
56
92
74
94
⫾
⫾
⫾
⫾
19
24
24
29
106
107
95
105
⫾
⫾
⫾
⫾
31*
14†
22†
21‡
62 ⫾ 22
49 ⫾ 23
55 ⫾ 25
98 ⫾ 10*
120 ⫾ 29*
113 ⫾ 36*
Definition of abbreviations: BMI ⫽ body mass index; COPD ⫽ chronic obstructive
pulmonary disease; FRC ⫽ functional residual capacity; HF ⫽ handgrip force; peak
V̇O2 ⫽ peak oxygen uptake; PEmax ⫽ maximal expiratory pressure; PImax ⫽ maximal
inspiratory pressure; QF ⫽ quadriceps force; TLC ⫽ total lung capacity; TL,CO ⫽
carbon monoxide diffusion capacity; 6MWD ⫽ 6-minute walking distance; Wmax ⫽
maximal workload.
Values are expressed as mean ⫾ SD.
* p ⬍ 0.0001.
†
p ⬍ 0.005.
‡
p ⫽ 0.06.
Assessment of Physical Activity Level in Daily Life
(Activity Monitoring)
Assessment was done with a triaxial accelerometer (DynaPort Activity
Monitor; McRoberts BV). It consists of a small and lightweight box enclosed in a belt worn on the waist and a leg sensor (total weight 375 g).
The DynaPort was recently validated in patients with COPD (10). It
measures precisely the time spent in walking, cycling, standing, sitting,
or lying, as well as movement intensity during walking, and is as accurate
as video recordings. Technical specifications of the activity monitor can
be found elsewhere (19).
Data from both groups were collected from March 2001 until
December 2004, covering therefore all yearly seasons during almost
4 consecutive years. Assessments were done on consecutive weekdays,
and each assessment day had 12 hours of duration, starting at the time
that the patient woke up. Mean starting time was similar in patients
with COPD and in healthy subjects (8:59 and 8:37 a.m., respectively).
Evening hours (e.g., after 8:59 p.m. in patients with COPD and after
8:37 p.m. in healthy elderly subjects) were not included in the analysis
because it is likely that elderly people in general have considerably
fewer activities during this period when compared with the other periods
of the day (see Assessment during Daytime in the online supplement,).
All subjects were carefully instructed on how the device should be
positioned, and they received a manual with clear instructions and
figures. Patients also had to fill out a checklist to verify if their day was
representative and to describe any possible hindrance of the activity
monitor.
Complete “blinding” to the evaluation device was not possible because the subjects had to consent formally to take part in the study, and
they had to be given some basic information about the measurements in
the informed consent. However, both groups (patients and healthy
individuals) had similar information. They were told only that it was a
“device able to distinguish which movements were performed during
the day.” Therefore, they were not aware that the aim of the research
was to quantify time spent in each activity. In addition, subjects were
told that a condition to take part on the study was that they should
keep their daily activity completely unchanged while wearing the device.
TABLE 2. COMPARISON OF COMORBIDITIES FOUND IN
PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY
DISEASE AND HEALTHY ELDERLY SUBJECTS
History of
Obesity*
Back pain on most days
Osteoporosis
Diabetes
Stable heart disease†
Hypertension‡
Arthritis (knee, hip, or shoulder)
Vascular disorders§
Depression||
Smoking¶
Patients with
COPD (n ⫽ 50)
6
8
6
4
16
9
14
3
8
50
(12%)
(16%)
(12%)
(8%)
(32%)
(18%)
(28%)
(6%)
(16%)
(100%)
Healthy Elderly
Subjects (n ⫽ 25)
3
4
1
1
4
4
6
1
2
10
(12%)
(16%)
(4%)
(4%)
(16%)
(16%)
(24%)
(4%)
(8%)
(40%)
Definition of abbreviation: COPD ⫽ chronic obstructive pulmonary disease.
* Body mass index ⬎ 30 kg/m2.
†
In patients with COPD: mild atrial arrhythmia controlled with medication (n ⫽
6), ischemic heart disease in the past (n ⫽ 5), or dilated cardiomyopathy (n ⫽ 5);
in healthy elderly subjects: mild arrhythmia controlled with medication (n ⫽ 4).
‡
Under current antihypertensive treatment.
§
Peripheral arterial insufficiency or venous thrombosis.
||
Clinically diagnosed depression.
¶
Ex-smokers or current smokers.
974
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 171 2005
To determine the necessary number of assessment days, we studied
the intraclass reliability coefficient in an initial sample of 33 individuals
(18 patients with COPD and 15 age-matched healthy subjects), in which
activity monitoring was performed during 5 consecutive days (Monday–
Friday). This allowed us to determine the number of days necessary to
achieve a between-day intraclass reliability coefficient of 0.70 or greater,
which is considered as acceptable to assess reliably a variable in a group
of individuals (20). The results of this analysis are described in detail
in the online data supplement. Briefly, it was concluded that, to assess
cross-sectionally walking time, standing time, sitting time, lying time, and
movement intensity during walking time in daily life in that group of
subjects, 2 days of assessment were necessary to achieve an acceptable
intraclass reliability coefficient (0.70 ⬍ intraclass reliability coefficient ⬍
0.88). Therefore, in patients assessed during 2 days, time spent in each
activity and body position was averaged over 2 assessment days. In the
subjects who performed 5 assessment days, the 2 days used in the
analysis were randomly selected using a random number generator
(21), and time spent in each activity and body position was also averaged
over these 2 selected days.
the single correlation between the DynaPort outcomes with physiologic
variables. The level of significance was set at p ⭐ 0.05.
In addition, day-to-day variability in physical activities in daily life
was studied with the coefficient of variation, and these results were
included in the online supplement.
RESULTS
As expected, patients with COPD were characterized by airflow
obstruction, hyperinflation, and reduced diffusion capacity. In
addition, severely reduced peripheral and respiratory muscle
force and pronounced reduction in functional and maximal exercise capacity were also observed. Healthy control subjects were
characterized by normal values in all these outcomes. Baseline
characteristics from both groups are described in Table 1.
Characteristics of Physical Activities in Daily Life
An overview of results concerning physical activities in daily life
is presented in Table 3. Compared with healthy control subjects,
patients with COPD had reduced walking time, standing time,
and movement intensity during walking in daily life (all p ⬍
0.0001). In addition, patients with COPD had higher sitting time
(p ⫽ 0.04) and lying time (p ⫽ 0.004). The proportion of time
spent in each of the activities and body positions during the day
is shown in Figure 1. Patients with COPD spent most of the day
(64 ⫾ 15%) in the sitting or lying position and only 6 ⫾ 4% in
walking, whereas in healthy elderly subjects, these proportions
were 46 ⫾ 16% and 11 ⫾ 4%, respectively.
Other Measurements
Pulmonary function (22), maximal inspiratory and expiratory pressures
(23), quadriceps force (24), handgrip force (25), maximal exercise capacity (26), and 6MWD (27) were assessed. All methods and equipment
are described in detail in the online supplement.
Sample Size and Power
A detailed description of the sample size calculation is provided in the
online supplement. In brief, using a two-sided ␣ ⫽ 0.05, a ␤ ⫽ 0.05 (or
power of 95%), and a hypothetical drop-out rate of 25%, 15 patients
in each group would be needed to show statistically significant differences in walking time between the two populations. We increased the
sample to its current size (50 patients with COPD and 25 healthy
subjects) for two reasons: (1 ) to cover the whole spectrum of COPD
severity by having enough patients in all disease stages and (2 ) to take
into account that the study involves correlations and multiple regression
models.
With the present sample size and using an ␣ ⫽ 0.05, the study had
more than 80% power to detect significant differences in each one of
the main variables studied (time spent walking, standing, sitting, and
lying in daily life, and movement intensity during walking). Details on
the power and sample size analysis are provided in the online supplement.
Correlates of Physical Activities in Daily Life
Table 4 offers a detailed overview on the single correlations
observed in patients with COPD. Walking time in daily life was
positively correlated with 6MWD (Figure 2), maximal workload,
peak oxygen consumption, quadriceps force, handgrip force, maximal inspiratory and expiratory pressures, FVC, FEV1, and diffusion
capacity (0.28 ⬍ r ⬍ 0.76, all p ⭐ 0.05). Standing time in daily life
was positively correlated with 6MWD, maximal workload, peak
oxygen consumption, FVC, total lung capacity, diffusion capacity,
handgrip force, and maximal inspiratory and expiratory pressures
(0.28 ⬍ r ⬍ 0.62, all p ⬍ 0.05). Movement intensity during walking
in daily life was correlated with 6MWD (r ⫽ 0.38, p ⫽ 0.006),
handgrip force and quadriceps force (r ⫽ 0.33 for both, p ⫽ 0.02),
and maximal workload (r ⫽ 0.31, p ⫽ 0.03).
Further analysis of our data showed that, in patients with
COPD, 6MWD accounted by itself for most of the variability in
the stepwise multiple regression models of walking time (partial
R2 ⫽ 0.56, p ⬍ 0.0001), standing time (partial R2 ⫽ 0.35, p ⬍
0.0001), and movement intensity (partial R2 ⫽ 0.23, p ⫽ 0.0007). No
other variable (including the use of oral corticosteroids, current
smoking status, and other comorbidities) contributed significantly to the explanation of walking time, standing time, and
movement intensity in walking in daily life.
Statistical Analysis
Statistical analysis was performed using the SAS version 8 statistical
package (SAS Institute, Cary, NC) and the GraphPad Prism 3
(GraphPad Software, San Diego, CA). Normal distribution was checked
with the Kolmogorov-Smirnov test. The only variable that showed
nonnormal distribution was cycling time, both in patients with COPD
and in healthy elderly subjects.
A comparison of time spent in different activities between patients
with COPD and healthy control subjects was done with an unpaired
t test, except for cycling time, in which the equivalent nonparametric test
(Mann-Whitney) was used. A stepwise multiple regression analysis was
performed to assess independent contributors to the variance in walking
time in daily life in patients with COPD. Pearson’s coefficient was used for
TABLE 3. CHARACTERISTICS OF PHYSICAL ACTIVITIES IN DAILY LIFE IN PATIENTS WITH
CHRONIC OBSTRUCTIVE PULMONARY DISEASE AND HEALTHY ELDERLY SUBJECTS
Patients with
COPD (n ⫽ 50)
Walking time, min
Cycling time, min
Standing time, min
Sitting time, min
Lying time, min
Movement intensity during walking, m/s2
For definition of abbreviation see Table 2.
44
4
191
374
87
1.8
⫾
⫾
⫾
⫾
⫾
⫾
26
8
99
139
97
0.3
Healthy Elderly
Subjects (n ⫽ 25)
p Value
⫾
⫾
⫾
⫾
⫾
⫾
⬍ 0.0001
0.52
⬍ 0.0001
0.04
0.004
⬍ 0.0001
81
5
295
306
29
2.4
26
14
109
108
33
0.5
Pitta, Troosters, Spruit, et al.: Physical Activities in Patients with COPD
Figure 1. Percentages of time spent in each of the activities or body
positions in healthy subjects and patients with chronic obstructive pulmonary disease (COPD) during the day. Others ⫽ cycling or undetermined activity (2% in healthy elderly subjects and 3% in patients with
COPD).
In healthy elderly subjects, walking time in daily life was
positively correlated with peak oxygen consumption (r ⫽ 0.47,
p ⫽ 0.02) and maximal workload (r ⫽ 0.45, p ⫽ 0.02), and
negatively correlated with body mass index (r ⫽ ⫺0.47, p ⫽
0.02). Standing time was correlated with FVC (r ⫽ 0.47, p ⫽
0.02) and total lung capacity (r ⫽ 0.42, p ⫽ 0.04). Stepwise
multiple regression showed that peak oxygen consumption was
the only variable to contribute significantly to the model of
walking time in healthy elderly subjects (R2 ⫽ 0.35, p ⫽ 0.003).
Age and sex were not significantly related to any outcome of
the activity monitor in both populations.
TABLE 4. SINGLE CORRELATION COEFFICIENTS BETWEEN
WALKING AND STANDING TIME VERSUS PHYSIOLOGIC
VARIABLES, AGE, AND BODY MASS INDEX IN PATIENTS
WITH CHRONIC OBSTRUCTIVE PULMONARY DISEASE
(N ⫽ 50)
Age, yr
BMI, kg/m2
Pulmonary function
FEV1, %pred
FVC, %pred
FRC, %pred
TLC, %pred
TL,CO, %pred
Muscle function
QF, %pred
HF, %pred
PImax, %pred
PEmax, %pred
Exercise capacity
6MWD, %pred
Wmax, %pred
Peak V̇O2, %pred
Walking Time (min)
Standing Time (min)
0.13
⫺0.08
0.12
⫺0.17
0.28*
0.36*
0.02
0.19
0.38†
0.21
0.30*
0.17
0.34*
0.34*
0.45†
0.44†
0.30*
0.36*
0.20
0.28*
0.29*
0.31*
0.76‡
0.64‡
0.33*
0.62†
0.56†
0.30*
Definition of abbreviations: BMI ⫽ body mass index; FRC ⫽ functional residual
capacity; HF ⫽ handgrip force; peak V̇O2 ⫽ peak oxygen uptake; PEmax ⫽ maximal
expiratory pressure; PImax ⫽ maximal inspiratory pressure; QF ⫽ quadriceps force;
TLC ⫽ total lung capacity; TL,CO ⫽ carbon monoxide diffusion capacity; 6MWD ⫽
6-minute walking distance; Wmax ⫽ maximal workload.
* p ⭐ 0.05.
†
p ⬍ 0.01.
‡
p ⬍ 0.0001.
975
Figure 2. Plot of 6-minute walking distance (6MWD; in m) and walking
time in daily life (minutes/day) assessed during 12 hours/day in patients
with COPD (closed circles; n ⫽ 50) and healthy elderly subjects (open
circles; n ⫽ 25). In patients with COPD, R2 ⫽ 0.56, p ⬍ 0.0001. In
healthy elderly subjects, R2 ⫽ 0.07, p ⫽ 0.3.
DISCUSSION
The present study clearly showed that most patients with COPD
spend significantly less time walking and standing and more time
sitting and lying in daily life when compared with sedentary
healthy elderly subjects. In addition, when patients with COPD
do walk, they walk significantly slower than healthy subjects.
Finally, the present study showed that a reduced 6MWD is the
best surrogate marker of inactivity during daily life in patients
with COPD.
Inactivity in COPD is not a surprising finding on itself. Others
have used different tools to suggest that patients with COPD
are less active compared with a control group. By using “activity
counts” as outcome, Schonhofer and coworkers (9) and Singh
and Morgan (28) described that patients with COPD had levels
of daily movement counts that were lower than the average level
recorded in age- and sex-matched healthy subjects. However,
the devices used in these studies are unable to provide detailed
information on time spent in different activities in real life and
are likely less sensitive than triaxial accelerometers (29). Therefore, this is the first study to show detailed differences between
patients with COPD and healthy control subjects in terms of
time spent in different activities and positions, as well as in
intensity of activities such as walking. Our results showed that
patients with COPD not only walk less time per day when compared with age-matched healthy subjects, but also walk 25%
slower (i.e., at a lower movement intensity). The degree of sedentary behavior in patients with COPD is further illustrated by
the fact that they spent 12% of the time during the day (or twice
the walking time) in the lying position, as compared with 4%
in healthy elderly subjects. It is also important to note that
individuals from both groups spent a large part of the day in
the sitting position, which seems to be a characteristic of the
elderly, whether or not they have a disease (30).
The American College of Sports Medicine states that individuals of all ages should maintain a minimum of 30 minutes of
moderate exercise (e.g., walking) per day to maintain or develop
fitness (1). Our study shows objective data on physical activity
in daily life, providing an accurate insight on this important issue.
In the present study, none of the 25 subjects included in the
healthy group showed less than 30 minutes of walking time per
day in both assessment days. In contrast, 15 of the 50 patients
with COPD (30%) did not reach 30 minutes of walking time per
day in both assessment days. In addition, even in those patients
with walking time exceeding 30 minutes per day, the movement
intensity was 17% lower than the movement intensity observed
in healthy elderly subjects (2.0 ⫾ 0.3 vs. 2.4 ⫾ 0.5 m/second2;
p ⫽ 0.008). This finding shows that even the most active patients
976
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 171 2005
with COPD probably walk at an intensity insufficient to bring
benefits in terms of fitness maintenance. Furthermore, GarciaAymerich and colleagues (31) suggested that inactivity is a risk
factor for hospital readmission in COPD. According to the
threshold in their study (walking at least 60 minutes/day every
day), 74% of the patients included in the present study can
be considered “at risk.” These results raise concerns about the
sedentary lifestyle in patients with COPD. Referral for pulmonary rehabilitation programs and encouragement to be more
active in daily life should be an important part of the management of patients with COPD because inactivity may influence
their clinical evolution.
Previous studies have shown significant correlation between
motion counts (reported as “vector magnitude units”) and
6MWD (32, 33). Nevertheless, correlation of 6MWD with more
accurate measures of physical activity level, such as walking time,
standing time, and movement intensity during walking in real
life, had never been previously described. In addition, the
6MWD was the only variable to enter the multiple regression
model for these variables. These findings further validate the
6MWD, a simple test and easy to incorporate in the clinical
routine (34, 35), as a test to reflect the functional exercise level for
daily physical activities (36). In contrast to the 6MWD, outcomes
such as peripheral muscle force and maximal exercise capacity
showed more modest correlations with walking and standing
time in real life. In addition, our results also showed that impairment in terms of airflow obstruction was weakly associated with
lower activity level in daily life (see also online supplement).
These results indicate that, in patients with COPD, physical
activities in daily life are better predicted by a “global” or “integrative” test (e.g., 6MWD) rather than by tests focused on single
components of physical functioning, such as lung function and
muscle force. In fact, our study showed that 6MWD was capable
of identifying patients with COPD who had low walking time
during daily life. As shown in Figure 2, 16 of 20 patients with a
6MWD of less than 400 m (or ⵑ 60%predicted) had an average
walking time of less than 30 minutes/day. Therefore, these patients surely cannot meet the minimum value recommended
by the American College of Sports Medicine guidelines (1). In
addition, three of the remaining four patients with a 6MWD of
less than 400 m also had also low walking time in daily life
(33–39 minutes/day, at intensities 21% lower than the average
found in healthy elderly subjects). In contrast, in patients with
a 6MWD higher than 400 m or 60%predicted, neither 6MWD
nor any other variable in this study was able to predict accurately
walking time in daily life. In other words, if the 6MWD is severely
reduced, patients are markedly inactive in daily life. However,
in patients with COPD with a higher 6MWD, physical activities
in daily life are highly variable, hardly predictable, and require
objective measurement. An important issue that remains to be
elucidated is whether changes in 6MWD are related to changes
in walking time in real life after interventions such as pulmonary
rehabilitation programs. Concerning healthy elderly subjects,
the 6MWD did not correlate to walking time in daily life (r ⫽
⫺0.02, p ⫽ 0.9).
Both groups had similar a prevalence of some comorbidities
that one can argue as possible limiting factors to the performance
of physical activities in daily life (high blood pressure, back pain,
arthritis, obesity). In addition, none of the patients in both groups
reported to feel impaired in daily life by these factors. Furthermore, no electrocardiographic abnormalities or clinical signs suggestive of severe cardiac disease that could impair the performance
of usual physical activities were detected during the maximal
cycling test in any subject from both groups. Therefore, patients
were matched for comorbidities as far as this is possible when
comparing these two populations. However, because patients
with COPD tend to have higher prevalence of some comorbidities than the general elderly population (e.g., depression [17],
osteoporosis [16], heart disease [18]), matching the populations
for these comorbidities could arguably result in selection bias.
In addition, as expected because of the disease itself, the use of
oral corticosteroids had higher prevalence in the COPD group.
However, use of oral corticosteroids, current smoking status, and
other comorbidities did not account significantly for variation in
the multiple regression models of walking time, standing time,
and movement intensity in daily life. Therefore, physical activities in daily life were reduced in patients with COPD independently of these factors.
Limitations of the present study include the fact that the
technique used for activity monitoring, although very precise if
properly applied, is susceptible to misplacement of the device
by the subjects and technical problems, which were the two
reasons to consider an assessment day as invalid. Concerning
misplacement of the device, although subjects were carefully
instructed on how the activity monitor should be positioned and
received a manual with clear instructions and figures, misplacement occurred in seven subjects, all of them patients with
COPD. This is an interesting finding, especially for those who
plan to perform research with activity monitoring in patients
with COPD in the future. Concerning technical problems with
the device, the proportion of subjects excluded for this reason
among the subjects assessed for 2 days was similar in both groups
(5 of 44 patients with COPD [11%] vs. 1 of 11 healthy elderly
subjects [9%]). Another limiting factor of the technique is the
cost of the device, which is higher when compared with other
motion sensors available on the market. In addition, there is a
need for technical expertise to use the software. These issues
limit the use of this tool for general clinical purposes. Furthermore, the DynaPort does not measure activities of the upper
extremity. This could lead to underestimation of overall energy
expenditure in case the outcomes of the device are translated
to kilocalories or metabolic equivalents, for example. It is also
important to note that other factors not investigated deeply in
the present study, such as oxygen desaturation (37) and depression (38), could also be correlated to daily activity.
In conclusion, patients with COPD are markedly inactive when
compared with healthy elderly subjects in daily life. The 6MWD
is the strongest correlate of walking and standing time during
daily life in patients with COPD. Patients with a severely impaired
6MWD are likely to have very low physical activity level in daily
life.
Conflict of Interest Statement : F.P. does not have a financial relationship with a
commercial entity that has an interest in the subject of this manuscript; T.T. does
not have a financial relationship with a commercial entity that has an interest in
the subject of this manuscript; M.A.S. does not have a financial relationship with
a commercial entity that has an interest in the subject of this manuscript; V.S.P.
does not have a financial relationship with a commercial entity that has an interest
in the subject of this manuscript; M.D. does not have a financial relationship with
a commercial entity that has an interest in the subject of this manuscript; R.G.
does not have a financial relationship with a commercial entity that has an interest
in the subject of this manuscript.
Acknowledgment : The authors thank the following professionals for their valuable help: Silvia Cecere (from the Department of Biostatistics, KU Leuven), Iris
Coosemans, Veronica Barbier, Anja Bocken, Pau Vilela, Ana Balanã, Sofie Mortier,
Monique van Vliet, Alix Debrock, and all the staff from Lung Function at the UZ
Gasthuisberg, Leuven, Belgium.
References
1. Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchaner D, Ettinger W, Heath GW, King AC, et al. Physical activity and
public health: a recommendation from the Centers for Disease Control
and Prevention and the American College of Sports Medicine. JAMA
1995;273:402–407.
Pitta, Troosters, Spruit, et al.: Physical Activities in Patients with COPD
977
2. Erikssen G. Physical fitness and changes in mortality: the survival of the
fittest. Sports Med 2001;31:571–576.
3. Yohannes AM, Baldwin RC, Connolly M. Mortality predictors in disabling chronic obstructive pulmonary disease in old age. Age Ageing
2002;31:137–140.
4. Oga T, Nishimura K, Tsukino M, Sato S, Hajiro T. Analysis of the factors
related to mortality in chronic obstructive pulmonary disease: role of
exercise capacity and health status. Am J Respir Crit Care Med 2003;
167:544–549.
5. Lee IM, Skerrett PJ. Physical activity and all-cause mortality: what is the
dose–response relation? Med Sci Sports Exerc 2001;33:S459–S471.
6. American College of Sports Medicine position stand. The recommended
quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med
Sci Sports Exerc 1998;30:975–991.
7. Bestall JC, Paul EA, Garrod R, Garnham R, Jones PW, Wedzicha JA.
Usefulness of the Medical Research Council (MRC) dyspnoea scale as
a measure of disability in patients with chronic obstructive pulmonary
disease. Thorax 1999;54:581–586.
8. Restrick LJ, Paul EA, Braid GM, Cullinan P, Moore-Gillon J, Wedzicha
JA. Assessment and follow up of patients prescribed long term oxygen
treatment. Thorax 1993;48:708–713.
9. Schonhofer B, Ardes P, Geibel M, Kohler D, Jones PW. Evaluation of
a movement detector to measure daily activity in patients with chronic
lung disease. Eur Respir J 1997;10:2814–2819.
10. Pitta F, Troosters T, Spruit MA, Decramer M, Gosselink R. Validation
of a triaxial accelerometer to assess various activities in COPD patients
[abstract]. Am J Respir Crit Care Med 2004;169:A594.
11. Foglio K, Carone M, Pagani M, Bianchi L, Jones PW, Ambrosino N.
Physiological and symptom determinants of exercise performance in
patients with chronic airway obstruction. Respir Med 2000;94:256–263.
12. Pitta F, Troosters T, Spruit MA, Mortier S, Barbier V, Coosemans I, Van
Vliet M, Decramer M, Gosselink R, et al. Physical activity level during
daily life in COPD patients and age matched healthy controls: preliminary results [abstract]. Am J Respir Crit Care Med 2004;167:A772.
13. Pitta F, Troosters T, Spruit MA, Mortier S, Barbier V, Coosemans I, Van
Vliet M, Decramer M, Gosselink R, et al. Physical activity level in daily
life in COPD patients and healthy elderly subjects [abstract]. Eur
Respir J 2004;24:631s.
14. Fabbri LM, Hurd SS. GOLD Scientific Committee. Global strategy for
the diagnosis, management and prevention of COPD, 2003 update.
Eur Res J. 2003;22:1–2.
15. World Medical Association Declaration of Helsinki. Ethical principles
for medical research involving human subjects. Bull World Health
Organ 2001;79:373–374.
16. Walsh LJ, Wong CA, Oborne J, Cooper S, Lewis SA, Pringle M, Coin
A, Inelman EM, Enzi G. Adverse effects of oral corticosteroids in
relation to dose in patients with lung disease. Thorax 2001;56:279–284.
17. Peruzza S, Sergi G, Vianello A, Pisent C, Tiozzo F, Manzan A, Hubbard
R, Tattersfield AE. Chronic obstructive pulmonary disease (COPD)
in elderly subjects: impact on functional status and quality of life.
Respir Med 2003;97:612–617.
18. Kjoller E, Kober L, Iversen K, Torp-Pedersen C. Importance of chronic
obstructive pulmonary disease for prognosis and diagnosis of congestive heart failure in patients with acute myocardial infarction. Eur J
Heart Fail 2004;6:71–77.
19. Brandes M, Rosenbaum D. Correlations between the step activity monitor
and the DynaPort ADL-monitor. Clin Biomechanics 2004;19:91–94.
20. Trost SG, Pate RR, Freedson PS, Sallis JF, Taylor WC. Using objective
physical activity measures with youth: how many days of monitoring
are needed? Med Sci Sports Exerc 2000;32:426–431.
21. Available from www.random.org (accessed December 2004).
22. Quanjer PH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault
JC. Lung volumes and forced ventilatory flows: report Working Party
Standardization of Lung Function Tests, European Community for
Steel and Coal. Official Statement of the European Respiratory Society. Eur Respir J Suppl 1993;16:5–40.
23. Rochester DF, Arora NS. Respiratory muscle failure. Med Clin North
Am 1983;67:573–597.
24. Decramer M, Lacquet LM, Fagard R, Rogiers P. Corticosteroids contribute to muscle weakness in chronic airflow obstruction. Am J Respir
Crit Care Med 1994;150:11–16.
25. Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M, Rogers S.
Grip and pinch strength: normative data for adults. Arch Phys Med
Rehabil 1985;66:69–74.
26. Jones NL, Makrides L, Hitchcock C, Chypchar T, McCartney N. Normal
standards for an incremental progressive cycle ergometer test. Am
Rev Respir Dis 1985;131:700–708.
27. Troosters T, Gosselink R, Decramer M. Six minute walking distance in
healthy elderly subjects. Eur Respir J 1999;14:270–274.
28. Singh S, Morgan MD. Activity monitors can detect brisk walking in
patients with chronic obstructive pulmonary disease. J Cardiopulm
Rehabil 2001;21:143–148.
29. Steele BG, Belza B, Cain K, Warms C, Coppersmith J, Howard J. Bodies
in motion: monitoring daily activity and exercise with motion sensors
in people with chronic pulmonary disease. J Rehabil Res Dev 2003;40:
45–58.
30. Coronado M, Janssens JP, de Muralt B, Terrier P, Schutz Y, Fitting
JW. Walking activity measured by accelerometry during respiratory
rehabilitation. J Cardiopulm Rehabil 2003;23:357–364.
31. Garcia-Aymerich J, Farrero E, Felez MA, Izquierdo J, Marrades RM,
Anto JM. Risk factors of readmission to hospital for a COPD exacerbation: a prospective study. Thorax 2003;58:100–105.
32. Belza B, Steele BG, Hunziker J, Lakshminaryan S, Holt L, Buchner
DM. Correlates of physical activity in chronic obstructive pulmonary
disease. Nurs Res 2001;50:195–202.
33. Steele BG, Holt L, Belza B, Ferris S, Lakshminaryan S, Buchner DM.
Quantitating physical activity in COPD using a triaxial accelerometer.
Chest 2000;117:1359–1367.
34. Troosters T, Gosselink R, Decramer M. Six-minute walk test: a valuable
test, when properly standardized. Phys Ther 2002;82:826–827.
35. Sciurba F, Criner GJ, Lee SM, Mohsenifar Z, Shade D, Slivka W, Wise
RA, and the National Emphysema Treatment Trial Research Group.
Six-minute walk distance in chronic obstructive pulmonary disease:
reproducibility and effect of walking course layout and length. Am J
Respir Crit Care Med 2003;167:1522–1527.
36. Brooks D, Solway S, Gibbons WJ. ATS statement on six-minute walk
test. Am J Respir Crit Care Med 2003;167:1287.
37. Soguel SN, Burdet L, de Muralt B, Fitting JW. Oxygen saturation during
daily activities in chronic obstructive pulmonary disease. Eur Respir
J 1996;9:2584–2589.
38. Kim HF, Kunik ME, Molinari VA, Hillman SL, Lalani S, Orengo CA,
Petersen NJ, Nahas Z, Goodnight-White S. Functional impairment in
COPD patients: the impact of anxiety and depression. Psychosomatics
2000;41:465–471.