ADAPTED PHYSICAL ACTIVITY QUARTERLY, 1997,14,43-50
O 1997 Human Kinetics Publishers, Inc.
Correlational Study of Three
Cardiorespiratory Fitness Tests
for Men With Mental Retardation
J.A. McCubbin
Oregon State University
P. Rintala
University of Jyvaskyla
G.C. Frey
Texas A&M University
Previous research has determined that there are few valid and reliable tests of
cardiorespiratory fitness.for men with mental retardation (MR). Though the
use of submaximal bicycle ergometry is a technique often used to predict
fitness in some samples, it has been questioned for persons with mental retardation. No studies have attempted to validate the use of a friction-braked bicycle ergometer as a method to estimate cardiorespiratory fitness in men with
mental retardation. Thus, the purpose of this study was to determine the correlation among three tests of cardiorespiratory fitness in men with MR.
Data were collected on 15 subjects (25.9 + 6.1 yrs.; 67.9kg + 13.5) with
mild MR. Subjects performed three tests: (a) submaximal A s t r a n d - ~ ~ h m i n ~
test on a friction-braked bicycle ergometer; (b) one-mile walk for time; and
(c) maximal incremental walking protocol on motorized treadmill. Results
from the three tests were: (a) predicted V 0 2 from bicycle ergometry was 43.54
+ 9.94 mlkglmin; (b) one-mile walk time was 13.9 + 2.3 min; and (c) V0,p
from the walking protocol was 40.36 + 10.53 mlkglmin. Regression analysis
of bicycle ergometry predicted VO,, and one-mile walk time revealed that
both exercise protocols were significantly correlated with V0,p from the maximal walking treadmill testing. Independent correlational analyses produced
coefficients of R = .64 for bicycle ergometry with VO,p, and R = - 3 4 for onemile walk time with V0,p. While both tests were significantly correlated with
laboratory-based treadmill testing VO,p, the one-mile walk time was a better
indicator of cardiorespiratory fitness compared to the bicycle ergometry predicted VO,.
Jeff McCubbin is with the Dep-nt
of Exercise and Sport Science at Oregon State
University, Corvallis, OR 97331. P. Rintala is with the University of Jyvaskyl$ Jyvaskyla,
Finland. G.C. Frey is with the Texas A&M University, College Station, TX 77843.
44
McCubbin, Rintala, and Frey
Several studies have established that, as a group, adults with mental retardation (MR) are particularly low in measures of cardiorespiratory fitness (Beasley,
1982; Coleman, Ayoub, & Friedrich, 1976; Pitetti, Rimmer, & Fernhall, 1993;
Schurrer, Weltman, & Bramrnel, 1985;Kittredge, Rimmer, &Looney, 1994).While
there is evidence to support that with adequate training opportunities subjects with
mental retardation can increase their level of cardiorespiratory fitness (Andrew,
Reid, Beck, & McDonald, 1979; Schurrer, Weltman, & Brammel, 1985;
Tomporowski & Jameson, 1985; Pitetti & Tan, 1991), procedures to assess cardiorespiratory fitness in this population are less clear (Seidl, Reid, & Montgomery,
1987; Lavay, Reid, & Cressler-Chaviz, 1990).
Most cardiorespiratory fitness tests are based on the premise that there is a
linear relationship between heart rate, oxygen uptake, workload, and energy expenditure. While this relationship is not based on intellectual level, assessing the
cardiorespiratory fitness of people with MR is difficult because of variations in
testing methodology, understanding the concept of best effort, cadence adherence,
variable performance by the participant because of learning or motivational changes,
and efficiency of movement (Seidl et al., 1987). There continues to be a need to
develop various valid and reliable field tests in order to determine the effectiveness
of different exercise programs for this population.
Cardiorespiratory fitness tests used with persons with MR have included
field tests and laboratory-based tests. Benefits of field tests include more subjects
can be tested at one time and little equipment is necessary. While there are several
alternatives for field testing cardiorespiratory fitness in persons without mental
retardation, fewer alternatives are available for persons with MR. Currently, there
appears to be five validated field tests that predict cardiorespiratory fitness for
individuals with mental retardation (Pitetti, Rimmer, & Fernhall, 1993). These include: the 1.5-mile walMrun (Fernhall & Tymeson, 1988), the 1.0-mile walk
(Rintala, Dunn, McCubbin, & Quinn, 1992), bicycle ergometry testing using the
Schwinn Air-Dyne (Pitetti & Tan, 1990), a modified Leger and Lambert shuttle
run, and the modified Canadian step test (Montgomery et al., 1992).
Pitetti and Tan (1990) demonstrated with a sample of 12 adults (8 males and
4 females) that using an air-braked bicycle ergometer (SchwinnAir-Dyne) seemed
to provide a valid means for assessing cardiorespiratory fitness as compared to
treadmill test results. While these data are encouraging, due to the relatively small
sample that included men and women, justification for additional support seems
warranted. Other investigators have attempted to determine the reliability of the
friction-braked bicycle ergometer as a means of assessing cardiorespiratoryfitness
in persons with mental retardation. Bundschuh and Cureton (1982) assessed the
test-retest reliability of adolescent-aged subjects with mental retardation using the
physical work capacity test (PWC 170) at R = 3 5 . Cressler, Lavay, and Giese
(1988) assessed the reliability of a modified physical work capacity test on a standard friction-braked bicycle ergometer in subjects with mental retardation and determined that for these subjects, the correlation coe=cient was relatively low at R
= 54. However, the validity of the values determined from a standard frictionbraked ergometer compared to values from laboratory-based assessment has not
been determined with this population. Because many of the bicycle ergometers
available for public use are the friction-brakedmodels, paired with the ever present
need to increase generalizability of research findings, it was determined that the
validity of bicycle ergometry testing should be determined.
Correlational Study
45
Researchers have speculated that certain submaximalbicycle protocols may
not be valid methods to predict cardiorespiratory fitness in this population. This
may be due to the lack of subject familiarity with cycling andlor the inability to
pedal against resistance during submaximal testing which may induce local
quadricep fatigue prior to steady state exercise. It has been demonstrated that subjects with poor levels of physical fitness may ungerestimate cardiorespiratory efficiency when being tested by cycle ergometer (Astrand & Rodahl, 1977). Though
this claim does not refer to subjects with mental retardation, it may be evident as
many studies have determined that subjects with mental retardation have lower
levels of fitness likely due to a sedentary lifestyle and lack of opportunity to exercise. It is important that multiple options are available, both for assessment and
program development, for persons with mental retardation. While there are data to
support the relationship between maximal treadmill tests and submaximal bicycle
ergometry in men without mental retardation, to date no studies have compared
the use of the maximal treadmill testing with the one-mile walk test and submaximal
friction-braked ergometry in men with MR. Therefore, the purpose of this study
was to determine the correlation among three tests of cardiorespiratory fitness in
men with MR. The findings from this study are essential to provide teachers and
other direct care providers with additional information to determine the most effective and efficient means of evaluating the cardiorespiratory fitness of men with
MR. Appropriate assessment and evaluation of cardiorespiratory fitness is essential in developing successful instructional programs related to the health and wellbeing of persons with MR.
Method
Subjects
Fifteen male subjects volunteered to participate (25.9 rt 6.06 years, weight 67.9 +
13.53 kg). Based on available IQ test results and input from the group home supervisors, the majority of the subjects were identified as having mild mental retardation. From the available past IQ records, the scores ranged from 42 to 68 (mean =
53). However, these IQ scores were not recent, varied in test used, and data were
not complete for all subjects. The men lived in community group homes or continued to reside with their parents and worked in community-supervised facilities.
Only men were chosen due to the limited number of females volunteering to participate. All of the subjects and/or their legal guardians gave informed consent
prior to participation in the study.
Experimental Protocol
All participants performed three exercise tests: (a) maximal exercise test on treadmill; (b) submaximal bicycle test; and (c) one-mile walk test. A 3-stage familiarization process was completed to increase the comprehension of testing requirements
and comfort with the testing situation (Reid, Dunn, & McClements, 1993; Rintala,
McCubbin, & Dunn, 1995).
Maximal Treadmill Test. The V0,p treadmill protocol required the subjects
to walk at 2.5 to 4 mph (depending on the individual's capability) at 0% grade for
2 minutes, followed by a 2.5% grade for 2 minutes. The grade was then increased
McCubbin, Rinfala, and Frey
46
2.5% every minute with a constant speed up to 20% grade. Beyond a grade of
20%, the speed was increased in one-minute intervals until the subject reached
volitional fatigue. A Quinton Model Q630A electrocardiograph was used to monitor the heart rate during the test. Blood pressure was taken every other minute
using a Quinton Model 410 device. A Parkinson Cowan (PC) dry gas meter was
used to measure the volume of inspired air. Expired air was measured with a S-3A
oxygen analyzer and a LB2 (CO,) analyzer from Beckman Instruments (Fullerton,
CA). Data samples were taken every 30 seconds and were interfaced into an IBM
personal computer. All subjects were tested by the same research team within a 2week interval.
One-Mile Walk Test. The Rockport one-mile walking test (Kline et al., 1987)
was conducted in an indoor facility on a measured 118-mile course that was marked
with cones. Specific verbal instructions were provided to "walk eight laps as fast
as you can, as if in a huny to go somewhere." Following a one-lap practice walk,
each subject walked with a testing assistant who stayed slightly in front of the
subject. Total walk time was recorded to the nearest second and used in the analyses. As a safety precaution, subjects wore a pulse monitor and receiver and heart
rates were recorded by the assistant following each lap. A minimum of 2 days rest
was allowed between treadmill test and one-mile walk test.
Submaximal Bicycle Test. All subjects performed a submaximal bicycle
test on a friction-braked bicycle ergometer using a modified Astrand-Ryhming
protocol (1954). Subjects pedaled at 50 revolutions per minute at workloads between 600 and 900 kpm for 6 minutes that produced a steady state heart rate between 130 and 150 bpm. Heart rate was taken every minute with the average heart
rate recorded during the 5th and 6th minutes. A computerized version (ftom Mt.
Sinai Hospital, Miami, FL) of the modified Wstrand-Ryhming nomogram (Astrand,
1960) was used to estimate VO, from submaximal heart rate values at a given
workload.
Data Analysis
Simple regression analyses were performed to evaluate the predictive ability of the
one-mile walk test and the submaximal bicycle test of the sample group. Statistical
analysis of the data were performed using Statgraphics5 12 for the Macintosh computer. Peak VO, from the treadmill testing was used as the criterion variable for
each analysis. An alpha level of 0.05 was established to indicate statistical significance (see Table 1).
Results
A significant (<0.05) negative correlation coefficient was determined between VOzp
and the one-mile walk time (R = -.84), and a significant positive correlation was
determined between VOzp and the bicycle ergometry test (R = .64). While both
correlations were determined to be significantly different from 0, as reflected by
the F statistic, further inspection of the data indicate more clearly why the onemile walking test is a better predictor of aerobic capacity in the sample studied.
The data presented in Table 2 illustrate some important factors in the analysis. The coefficients of determination (RZ),or the amount of variance that can be
explained, was .71 (one-mile walking test) or .41 (bicycle ergometer test). During
Correlational Study
47
Table 1 Descriptive Aerobic Performance Data for All Subjects
Peak VO, (treadmill)
Predicted VO, (bicycle protocol)
Mile time
Mean
SD
40.36 ml/kg/min
43.54 ml/kg/min
13.95 min
10.53 ml/kg/min
9.94 ml/kg/min
2.26 min
Table 2 Multiple Regression Summary Tables for VO, and Walk Time and Bicycle Test
Walk test
Bicycle test
14
14
.84
.64
.71
.41
Sfj. R2
Std. error
.689
,365
1.259
7.919
the bicycle ergometer test, 59% of the shared variance between the two tests could
not be explained, whereas with the one-mile walking test only 39% could not be
explained. Thus, the one-mile walking test is a better predictor of aerobic capacity
as measured by the VO,p on an incremental treadmill protocol in men with mental
retardation. The visual distribution of the data points generated from the study are
plotted in Figures 1 and 2. These scattergrams illustrate the distribution of scores
around the line of best fit for each test. The wider distribution of scores about the
line indicate the subjects' performance was more variable and less accurate in the
prediction of aerobic capacity. In general, the points around the line in Figure 1 are
closer to the line and, thus, supporting the use of the one-mile walk test.
Discussion
The findings of this study indicate men with mild mental retardation can successfully participate in two types of field tests to evaluate cardiorespiratory fitness.
Though both measures used in this study have acceptable levels of validity, the
one-mile walk test appears to be the better alternative to laboratory-based VO,
assessment. The figures demonstrate that the one-mile walk test does not appear to
overestimate or underestimate the aerobic performance in these subjects. This differs from the findings of Kittredge, Rirnmer, and Looney (1994) in which the predicted VO,p in a high percentage of the subjects was overestimated, based on the
one-mile walk time. It should be noted their sample (n = 25) included 12males and
13 females.
In this study, the bicycle test was a more difficult test to administer as subjects experienced problems with cadence adherence and handling changes in
workload. This required more practice in the preliminary stages prior to testing,
McCubbin, Rintala, and Frey
Time
Figure 1 - Scattergram and regression line for estimating aerobic capacity for men
with mental retardation when using the one-mile walking test.
Regression of Observed vs. Predicted Bicycle V
65
y = 10.818
I
+ 0.67852~ RA2= 0.410
2 0 4 . . - . 1 . . * . 1 . . . . 1 . - - . 1. . . . I . 20
25
30
35
40
45
l....l....l....l....I
50
55
60
65
70
V02max Predicted From Submaximal Bicycle Test (mVks/min)
Figure 2 - Scattergram and regression lines for estimating aerobic capacity of men
with mental retardation for the istrand Ryhming bicycle ergometer test.
Correlational Study
49
which in essence took more time and effort in test administration. The fact that
testing was more problematic, together with the supported evidence from the correlation analysis, justifies the use of the one-mile walking test as a preferred predictor of aerobic performance.
The subject pool was relatively small which may effect generalizability of
these findings. Further research to determine whether similar findings are noted
for other people with mental retardation, including females and individuals with
more severe levels of mental retardation, is warranted. In addition, evidence that
demonstrates that the one-rnile walk test can be valid and reliable without the use
of I-to-1 ratio of subjects to testing assistants is needed. It is hoped this information will be helpful to teachers and other practitioners that may need information
about cardiorespiratory fitness levels of persons with mental retardation. The results of this study further substantiate that a relatively easy to administer test, requiring only walking space and testing assistants, can provide meaningful
information to assist in monitoring the fitness levels of similar individuals. Perhaps teachers and other health-care providers can use this process of assessment to
justify the need for more programs and promote opportunities to improve physical
fitness in this population.
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