CONTRIBUTION FROM THE FIELD
Six-Minute Walk Test: A Potential
Outcome Measure for Hydrotherapy
S. E. Gowans, A. deHueck, and S. Voss
Hydrotherapy is a common treatment for patients
with rheumatic diseases and can be used to increase
physical function. To date, a variety of outcome measures have been used to evaluate the effect of hydrotherapy on physical function. Most studies have employed outcome measures for impairments such as
pain (1–3), decreased strength (4), decreased range of
motion (1–3,5), decreased cardiovascular fitness (4 –
6), or inflammation (2,5–7) that can impede function.
A smaller number of studies have had patients selfreport their function using standardized questionnaires such as the Arthritis Impact Measurement
Scales (2,5), the Oswestry Low Back Pain Functional
Disability Questionnaire (3), or the Health Assessment Questionnaire (6). Finally, a few studies have
directly measured patients’ functional abilities by
measuring walking times (5,7), gait (8), or selected
activities of daily living (7). We believe the 6-minute
walk test (9) is another outcome measure that may be
useful in directly assessing physical function following hydrotherapy.
The purpose of this report is 2-fold. First, we
present preliminary results of the 6-minute walk test
as an outcome measure for hydrotherapy in 39 patients with rheumatic conditions. Our results pro-
S. E. Gowans, BSc(PT), BA, PhD, and A. deHueck, BSc(PT),
Department of Rehabilitation Services, The Toronto Hospital, and
Department of Physical Therapy, University of Toronto; and S.
Voss, BSc(PT), Department of Rehabilitation Services, The Toronto Hospital, Toronto, Ontario, Canada.
Address correspondence to S. E. Gowans, BSc(PT), BA, PhD,
Department of Rehabilitation Services, The Toronto Hospital, 200
Elizabeth Street, Toronto, Ontario, M5G 2C4 Canada.
Submitted for publication September 24, 1998; accepted in
revised form February 10, 1999.
© 1999 by the American College of Rheumatology.
208
vide a sense of the range and variability of 6-minute
walk distances at baseline and the magnitude of
change on retesting. Second, we include unpublished results on the use of the 6-minute walk test in
other patients with fibromyalgia. We use these unpublished results, in conjunction with published
data, to address methodologic issues regarding the
use of the 6-minute walk test as a hydrotherapy outcome measure for patients with rheumatic diseases.
Background on the 6-minute walk test
A 12-minute run/walk test was originally developed
to assess the physical fitness of healthy subjects (10).
This test was modified to a 12-minute walk only test
(11) to assess function in patients with chronic bronchitis. A 6-minute walk test was later recommended as
the walk duration of choice because it represented a
reasonable compromise between the ease of administering a shorter test and the greater discriminative
power of a longer test (9). The 6-minute walk test was
validated as a measure of physical function by demonstrating that walk distances correlated with oxygen
consumption and self-reported physical function in
patients with heart failure or respiratory disease (12).
Although this test is now commonly used to assess
function in patients with cardiorespiratory disease, it
has only recently been used in patients with rheumatic
diseases to evaluate the effect of land-based exercise
programs (e.g., refs. 13,14).
Using the 6-minute walk test to evaluate
hydrotherapy
At our urban tertiary care center, a subset of outpatients with rheumatic diseases are referred solely
for hydrotherapy and join an ongoing exercise class
0893-7524/99/$5.00
6-Minute Walk Test and Hydrotherapy 209
Arthritis Care and Research
Table 1. Patient characteristics*
Group
Subjects
(n)
Sex
(Women/men)
Age
(years)
Number of pool
classes
Treatment
interval (days)
Fibromyalgia
Rheumatoid arthritis
Back
Lower extremity
Other
All
16
7
7
6
3
39
14/2
6/1
7/0
6/0
2/1
35/4
51.4 6 2.7
56.4 6 4.8
60.8 6 3.6
59.7 6 5.0
48.3 6 3.1
55.0 6 2.0
14.6 6 1.0
14.6 6 1.3
14.4 6 1.3
12.7 6 2.0
14.7 6 1.9
14.3 6 0.6
88.3 6 11.7
73.4 6 9.5
83.3 6 6.3
79.7 6 15.9
85.3 6 9.8
83.2 6 5.7
* Baseline characteristics of patients by diagnostic group. The treatment interval was calculated for each patient as the number of days between the first and
last hydrotherapy class. Variability is expressed as mean 6 SEM.
in a warm, therapeutic pool. Pool classes are 30
minutes long and consist of 20 minutes of range of
motion exercises against water resistance (all joints)
and 10 minutes of ambulation. Patients attend approximately 2 classes per week to a maximum of 15
classes prior to discharge.
In the last 2 years, outpatients with rheumatic
diseases who received hydrotherapy alone have
completed a 6-minute walk test on the first and last
days of hydrotherapy (prior to entering the pool).
Walk tests were conducted by the physiotherapist
assigned to the pool in a corridor where a 42-meter
distance was marked in 1-meter increments on tape
permanently adhered to the wall baseboard. Patients
were instructed to walk between wall markers for 6
minutes at a fast, comfortable pace. Patients received
no encouragement during the test. Total distance
walked was recorded by the therapist to the nearest
meter. Immediately following the walk test, patients
also indicated their rate of perceived exertion using
a 15-point categorical scale, score range: 6 –20 (15).
Six-minute walk distances were collected retrospectively in 1996 (n 5 20) and prospectively in 1997 (n 5
19). To date, we have tested 39 outpatients with rheumatic diseases who received hydrotherapy alone.
These patients were arbitrarily divided into 5 diagnostic groups: fibromyalgia (n 5 16), rheumatoid arthritis
(n 5 7), lower extremity problems (n 5 6), back pain
(n 5 7), and other (psoriatic arthritis, scleroderma, and
systemic lupus erythematosis, n 5 3).
Six-minute walk distances for all patients were compared pre- and post-hydrotherapy using a paired t-test
(1-tailed). One-way analyses of variance were used to
probe for differences between diagnostic groups in patients’ ages, treatment characteristics (number of pool
classes, number of days between the first and last pool
class), baseline 6-minute walk distances, and distance
gains. Distance gains were also categorized by baseline
distances to assess the walk test’s sensitivity to treatment-induced changes across a range of baseline values. Statistical significance for all analyses was set at
P , 0.05. Variability, when noted, is expressed as
standard errors of the mean.
Patient demographics, treatment variables, and
baseline distances were similar (P . 0.05) across the
5 diagnostic groups (see Tables 1 and 2). Six-minute
walk distances were significantly increased following hydrotherapy (pre: 295.9 6 12.7 m; post: 346.9 6
12.7 m, difference: 51 m, P , 0.0001). Rates of perceived exertion, completed in 25 of 39 patients, were
unchanged (pre: 13.0 6 0.4; post: 13.2 6 0.3), despite
similar and significant gains (144 m, P , 0.002) in
6-minute walk distances.
Gains in walk distance were not related to a patient’s diagnosis since gains did not vary across diagnostic groups (although our small numbers per
Table 2. Six-minute walk distances (pre- and post-hydrotherapy)*
Group
Distance (pre)
Distance (post)
Difference (post 2 pre)
Fibromyalgia
Rheumatoid arthritis
Back
Lower extremity
Other
All
319.2 6 15.2
286.6 6 37.9
239.1 6 12.0
277.3 6 37.3
363.0 6 69.4
295.9 6 12.7
377.0 6 17.3
356.0 6 32.5
281.1 6 15.4
311.5 6 34.4
389.3 6 55.3
346.9 6 12.7
57.8 6 13.9
69.4 6 35.3
42.0 6 19.6
34.2 6 53.8
26.3 6 25.1
51.0 6 12.0
* Six-minute walk distances in meters by diagnostic group. Variability is expressed as mean 6 SEM.
210 Gowans et al
Figure 1. Gains in 6-minute walk distances post-hydrotherapy classified by walk distances at baseline.
diagnostic group limited the power of this analysis).
Gains did vary significantly by baseline distance,
with patients with lower baseline distances showing
the greatest gains (P , 0.005; see Figure 1).
Final comments
Six-minute walk distances can be increased in
patients with rheumatic diseases following hydrotherapy. Because we saw greater gains in patients
with lower baseline distances, the 6-minute walk
test may be more sensitive to change in patients with
lower physical function. This conclusion is reinforced by others who found an inverse correlation
between baseline distances (after 4 practice trials)
and distance gains in patients with chronic heart
failure who had received 3 weeks of exercise training
(16). Unfortunately, increases in 6-minute walk distances alone are insufficient to document the effectiveness of hydrotherapy since walk distances (of
various duration) can be increased by practice
(9,11,17–19) and encouragement (17).
Only one study has examined the effect of practice
on 6-minute walk distances. This study (17) reported
a small but significant practice effect (115 m, interpolated from data presented graphically) in the absence of encouragement on 6-minute walk distances.
We have replicated this small practice effect (112 m,
trial 1: 399 6 14 m; trial 2: 411 6 12 m) in 56
fibromyalgia patients who were enrolled in exercise
studies at our center, t(55) 5 1.94, P , 0.03 (Gowans
et al: unpublished observations). These fibromyalgia
patients completed two 6-minute walk tests without
encouragement, either 6 weeks (n 5 20) or 2 to 3
Vol. 12, No. 3, June 1999
days apart (n 5 36). While it is tempting to infer
therapeutic benefits by comparing distance gains in
an uncontrolled design to published practice effects,
we believe this is unwise. Our reservations stem
from our own observation that practice effects varied
inversely with baseline distance in our 56 fibromyalgia patients, F(3,52) 5 10.1, P , 0.00002 (Figure 2).
This novel observation, which needs to be replicated, suggests that the magnitude of the practice
effect may be specific to the baseline distances in the
sample.
The strongest design to address practice effects is a
randomized, controlled trial where patients are randomly assigned to a control or hydrotherapy group
and then complete one or more walking trials at
baseline. Using this design, hydrotherapy can be
deemed effective if gains shown by the hydrotherapy
group exceed those shown by the control group.
However, such a design is not easy to employ in
clinical settings. Practice effects can also be addressed with an uncontrolled design if patients are
given multiple walking tests at baseline. Guyatt and
colleagues advocated two practice trials, but their
graphic data (17) suggest that one practice trial may
be sufficient for group analyses if patients receive no
encouragement during the test.
Regardless of the study design chosen, we believe
patients should not be given verbal feedback nor
should testers walk with patients during the test, as
encouragement can enhance practice effects (17). Patients should also be required to rate their level of
perceived exertion following the test to ensure that
Figure 2. Practice effects observed in 6-minute walk distances in patients with fibromyalgia (n 5 56) who were
enrolled in other exercise studies. A practice effect was
defined as the difference in distance between the second
and first trial of the 6-minute walk test. Trials were 6
weeks (n 5 20) or 2 to 3 days (n 5 36) apart.
6-Minute Walk Test and Hydrotherapy 211
Arthritis Care and Research
distance gains are not due to greater effort on retesting (another potential confound).
Providing that confounds are addressed, we believe multiple features of the 6-minute walk test
commend its use. First, the 6-minute walk test is an
objective measure of physical function and, thus,
avoids the potential bias of self-report. Second, it
measures walking, an important functional ability.
Third, it is simple and inexpensive to administer
and, unlike questionnaires, requires no proficiency
in written English. Fourth, it is a self-paced activity
that can be completed by patients with a wide range
of functional abilities, including patients with very
low physical function.
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