determining metabolic equivalent values of physical activities for persons with paraplegia
TRANSCRIPT
RESEARCH PAPER
Determining metabolic equivalent values of physical activities forpersons with paraplegia
MIYOUNG LEE1, WEIMO ZHU2, BRAD HEDRICK3 & BO FERNHALL2
1Department of Nutrition and Exercise Sciences, Oregon State University, Corvallis, Oregon, USA, 2Department of
Kinesiology and Community Health, and 3Division of Disability Resources and Education Services, University of Illinois at
Urbana-Champaign, Urbana, Illinois, USA
Accepted June 2009
AbstractPurpose. The compendium of physical activity (CPA) may not be appropriate for persons with paraplegia (PP) because oftheir possible low resting metabolic rate (RMR), or 1 MET, and a lack of physical activities (PAs) engaged by PP in the CPA.A CPA supplement, therefore, is needed. The purpose of this study was to examine the feasibility of constructing a shortsupplement for PP with two specific aims: to determine whether PP need an alternative 1-MET value and if selected PA canbe classified into corresponding categories based on their ‘engagement’ and ‘energy expenditure (EE)’ characteristics.Method. Thirty-one PP (161.26 cm+ 22.99 cm, 60.52 kg+ 15.32 kg, and 24.16+ 6.25 years) were recruited. RMR and10 PA with different intensities were measured using indirect calorimetry. The z- and t-tests were employed to examineMET difference between the measured values and those of CPA (a¼ 0.05).Results. One-MET for PP (3.1 mL/kg/min) was lower than that of the CPA (3.5 mL/kg/min). Although some MET valueswere found to be similar to those in the CPA, others were statistically significantly different.Conclusions. To be able to measure PA-related EE of a disability subpopulation using the CPA accurately, a supple-ment that accounts for the impact of different types of activities and the EE characteristics of the subpopulation must bedeveloped.
Keywords: Energy expenditure, physical activity, disability
Introduction
There are about 250 000 individuals with spinal cord
injury (SCI) in the United States, including about
50% with tetraplegia and 50% with paraplegia,
whose injury levels are classified above or below the
first thoracic vertebra, respectively [1]. Individuals
with SCI are more susceptible to health pro-
blems such as stroke, osteoarthritis, heart disease,
rheumatoid arthritis, diabetes, etc. compared with
able-bodied individuals [1]. Promoting regular par-
ticipation of physical activities (PAs) is critical for the
quality of life of people with SCI [2] and an accurate
and practical way to measure PA of people with SCI
is essential for this goal. Self-report questionnaires
are one of the most popular PA measures to
estimate the PA-related energy expenditure (EE)
for non-disabled populations because it is inexpen-
sive and easy to administer compared with the other
PA measures, such as doubly labeled water, indirect
calorimetry, or motion sensors [3,4]. In addition,
some questionnaires provide detailed accounts of the
time, intensity, and patterns of PA and EE in free-
living conditions [5–8].
Although a few questionnaires [9] have been
developed to measure PA of individuals with SCI,
they were not designed to estimate EE. When
estimating EE from questionnaires or other self-
report measures (e.g. diary), the metabolic equiva-
lents (MET) of PA must be known. One (1) MET is
assumed to equal the amount of energy expended
during 1 min at rest, which is roughly 3.5 mL of
oxygen per kilogram of bodyweight per minute
(3.5 mL/kg/min) [5] or 1.2 kcal per minute for a
Correspondence: Miyoung Lee, Department of Nutrition and Exercise Sciences, Oregon State University, 103 Women’s building, Corvallis, Oregon 97331,
USA. E-mail: [email protected]
Disability and Rehabilitation, 2010; 32(4): 336–343
ISSN 0963-8288 print/ISSN 1464-5165 online ª 2010 Informa UK Ltd.
DOI: 10.3109/09638280903114402
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70 kg (150 lb) person. One MET is thus equivalent
to one’s resting metabolic rate (RMR). Using MET
estimations is a simple way of measuring PA intensity
and can be used to estimate the amount of oxygen
used by the body during PA. For example, three
METs of a PA means three times the RMR or
10.5 mL _VO2 (kg/min) required for that PA, but this
assumption is based on the presumed value of an
oxygen uptake of 3.5 mL/kg/min at rest.
To help using MET values to estimate EE using
questionnaires, diary or observation, a major national
effort was made to compile the MET values of PA
together. As a result, a total of 605 PAs have been
compiled, with assigned MET values, in a list known
as the compendium of physical activity (CPA) [5].
However, the MET calculation for persons with SCI
may be inaccurate because 1 MET of persons with
SCI may differ from that of able-bodied individuals.
According to a systematic review [10], RMR of
persons with SCI was *14–27% lower than able-
bodied individuals. Another study of 13 twins with/
without SCI also showed 10% difference of RMR
[11]. Thus, a person with SCI may exhibit a different
EE performing the same activity as a person without
SCI. In addition, most PAs included in the CPA are
for able-bodied individuals and only one PA is
defined specifically for persons with SCI (wheelchair
basketball). Consequently, the CPA is not currently
a useful tool for estimating EE of PA in persons with
SCI.
To be able to apply the CPA on persons with
disabilities, a CPA supplement that takes into
consideration the EE characteristics and types of
PA engaged regularly by a targeted subpopulation
must be developed. To do so, the relationship
between PA and persons with disabilities, and their
EE characteristics must be understood. On the basis
of the characteristics of ‘engagement’ and ‘EE
characteristics’, PA of persons with disabilities can
be generally classified into four categories: (1)
Activity by Able-bodied population Only (AAO),
(2) Activity by Both able-bodied and disability
populations with Similar METs (ABS), (3) Activity
by Both able-bodied and disability populations with
Different METs (ABD), and (4) Activity by a
targeted Disability population Only (ADO). There-
fore, to be able to apply the CPA to a population
with a disability, the activities belonging to AAO
and ABS must be identified and the MET values of
ABD and ADO activities must be re-estimated/
estimated. Including ABS, ABD with redefined
MET values, and ADO activities a supplement
compendium can be developed and applied to a
targeted population with disabilities (see Figure 1
for a visual presentation of the hypothetical supple-
ment concept).
The purpose of this study was to examine the
feasibility of constructing a short supplement to the
CPA for persons with SCI focusing on paraplegia
only. To achieve this, two specific aims were
investigated whether: (a) persons with paraplegia
(PP) need an alternative 1 MET value, which is used
to determine MET values of PAs and (b) selected PA
and their corresponding categories (i.e. ABD, ABS,
Figure 1. PA compendium and its supplements for disability subpopulations.
MET for paraplegia 337
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and ADO) can be confirmed based on the
characteristics of the ‘engagement’ and ‘EE
characteristics.’
Methods
Participants of selected subpopulation
A total of 31 participants with paraplegia (PP, 19
males and 12 females) were recruited considering a
variety of injury levels and completeness of lesions.
Six had an injury level between T3 and T6 and 25
had an injury level at T7 or below. These two groups
of injury levels were determined by the physical
responses (e.g. _VO2 peak), sitting balance, walking
potential and muscle innervations, which were split
at thoracic cord injury six or above [12–14]. The
participants were also classified using American
Spinal Injury Association Impairment Scale [15]
and the levels of paraplegia were between A and D
(14 As, 6 Bs, 5 Cs, 4 Ds, and 2 spinal bifida).
Participants’ causes of SCI are varied from the birth
to traumatic accidents. The study was approved by
the University of Illinois at Urbana-Champaign’s
institutional review board and all subjects signed
informed consent prior to participation.
Selection of physical activities
Participants’ EE was measured when performing 10
PAs selected for this study. The selection of these
specific activities was based on considerations of the
PA intensity in PP. Of the 10 activities selected, three
activities were considered as low-intensity (53
MET), four activities as moderate-intensity (�3
MET, but �5.9 MET), and three activities as high-
intensity (�6 MET) based on the PA recommenda-
tion by the American College of Sports Medicine
and the American Heart Association [16] and the
CPA [5].
Classification of physical activities
The selected PAs were then classified into four
categories as it was briefly explained in the Introduc-
tion section, including: (a) AAO (e.g. forestry, ax
chopping fast: 17 METs [5]), (b) ABS (e.g. washing
dishes: able-bodied persons in standing position, 2.3
METs vs. lower level SCI persons in sitting position,
2.3 METs [17]), (c) ABD (e.g. vacuuming: 3.5
METs for able-bodied persons vs. 3.0 METs for
persons with lower level of SCI [17]), and (d) ADO
(e.g. wheeling on grass: persons with SCI (T4–T5),
6.1 METs [17]). Among 10 activities selected in this
study, three were considered ABS, three ABD, and
four ADO. Table I summarizes selected activities,
their estimated intensity levels (approximate MET
values), and the PA category. ADO MET values,
which are unique activities to PP, were selected
according to paraplegia literatures [17,13] and from
our own pilot study.
Data collection
Data on body composition, RMR, oxygen consump-
tion ( _VO2) during 10 PAs, and _VO2 peak were
collected. To complete all the tests, participants
visited the laboratory three times, and all tests were
completed within 14 days. Body composition, i.e.
fat-free mass (FFM) and body fat%, was measured
by dual energy X-ray absorptiometry (DXA; QDR
4500 Elite, Hologic, Bedford, MA).
RMR was measured by indirect calorimetry using
a canopy (Quark b2 with Canopy kit, COSMED,
Italy) in the early morning before the participants
typically start their day following a 12-h fast.
Participants were also asked to avoid vigorous PA
for 24 h prior to testing. The participants came to the
laboratory by car to reduce their PA prior to testing.
Participants were asked to take rest for about 30 min
in the supine position in an isolated room with the
temperature controlled between 218C and 248C
Table I. Selected PA and its intensity.
No. About METs Category Type of activity Specific activities
1 1.5 ABS Occupation Working on computer
2 1.0 ABS Inactivity, quiet Sitting and watching TV
3 1.8 ABS Miscellaneous Reading
4 �3, but �6 ADO Unique Pushing wheelchair on a tile floor
5 3.5 ABD Home activity Vacuuming
6 3.5 ABD Home activity Mopping
7 6.0 ABD Home activity Moving furniture, household items, or boxes
8 56 ADO Unique Pushing wheelchair on a sidewalk
9 56 ADO Unique Pushing on the ramp up
10 �3, but �6 ADO Conditioning exercise Arm ergo meter 60 W at 60 rpm
ABS, activity by both able-bodied and disability populations with similar METs; ABD, activity by both able-bodied and disability
populations with different METs; ADO, activity by a targeted disability population only.
338 M. Lee et al.
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before collecting data. Following the protocol devel-
oped by Haugen et al. [18], RMR was measured for
30 min, but the first 15 min of data were deleted and
only the last 15 min of RMR data were used for the
calculation. The collected RMR data were also used
for calculating the MET values to verify whether the
RMR of PP is the same as the RMR of able-bodied
persons (3.5 mL _VO2/kg/min)._VO2 of 10 PAs was collected by indirect calori-
metry (K4b2, COSMED, Italy) for 10 min each.
Before performing each PA, heart rate (HR) was
measured and the data collection was begun when
the HR was similar to resting HR (within+ 10
beats). All instruments were calibrated prior to the
data collection [19,20]. The participants performed
all PAs as close as possible to how they would
perform them in their daily lives. For working on
computer, reading, and watching TV, participants
sat quietly about 10 min first and then begun the
data collection. The participants were mopping on a
tile floor and vacuuming on a standard carpet. To
keep the experimental setting as natural as possible,
the room was filled with office furniture, such as
chairs, desks, tables, etc. Pushing on the tile was set
at a participant’s ordinary pushing speed and
pushing on the side walk was set at 40% faster than
pushing speed on the tile. Pushing on the ramp was
simulated to push up and down on of a long theater
or hospital hallway ramp. To control for a carry-over
effect or fatigue from previous PAs, a counter-
balanced design was employed [21]. Minute-by-
minute _VO2 data were used for calculating MET
values. The first 3 min and the last minute of _VO2
data were deleted to obtain stable data and the
average _VO2 of the remaining 6 min was used to
calculate the MET value of each activity.
Finally, a standardized arm ergometer discontin-
uous protocol [22–24] was employed to measure_VO2 peak in which the work rate was started at 0 W
for a warm up, and then was increased 10 W every
2 min with the crank rate at 60 (rev/min) throughout
the test. The participants took a 1-min rest between
each stage and their blood pressure was measured for
safety purposes during the rest period.
Data processing and statistical analysis
Measured oxygen consumption ( _VO2 mL/kg/min) of
RMR data was averaged to obtain 1 MET of PP and
the mean of a participant’s own RMR was computed
to calculate MET values. To calculate each partici-
pant’s observed MET values for 10 PAs from raw
data, the following formula (1) was employed:
METPA ¼_VO2 of PA ðmL=kg=minÞ
_VO2 of resting ðmL=kg=minÞð1Þ
The mean and standard deviation (SD) of the
MET value of each PA and the categories of PA were
classified. To determine the accuracy of the classi-
fication (e.g. if they are indeed ABS or ABD
activities), z-test was applied (Equation (2)):
z¼ Mean of observed MET values�MET value from CPA
SD of observed MET value
ð2Þ
When an absolute z-value is �1.96 [25], it
indicates that the observed MET values are different
from the MET values of the CPA (with Type I error
a¼ 0.05) and are classified as ABD. To scrutinize
the effect of 1 MET on MET values, the observed 1
MET of a PP and 1 MET of the CPA (3.5 _VO2 mL/
kg/min) were employed. To examine the difference
between MET values calculated using different 1
MET values, paired t-tests were applied.
The mean and SD of demographic variables by
group (e.g. gender, level of injury, and completeness
of lesions) were also calculated, and independent t-
tests were applied to examine the group difference.
Group difference of observed MET values was also
examined by independent t-tests. All alphas (a) were
set at 0.05. Bonferroni correction procedure was
employed to control Type I error when applicable.
All statistical analyses were completed using SPSS
15.0 software (SPSS, Chicago, IL) and related
software (e.g. Excel, Microsoft, Redmond, WA).
Results
The characteristics, physiological responses (e.g._VO2 or HR), and body composition of the partici-
pants by gender are reported in Table II. When
comparing group differences by gender, injury level,
or completeness of lesion, there were no statistical
differences between injury level and completeness of
lesion with p4 0.05 after Bonferroni correction.
There were gender differences in several variables.
RMR was found higher in males, p5 0.01 (1392+233 kcal/day vs. 1042+ 174 kcal/day), but the gen-
der difference disappeared when the RMR EE was
adjusted for FFM. Among the body composition
variables, only FFM and FAT% showed statistical
difference between genders.
One MET for the paraplegia group was 3.1
(+0.52) mL/kg/min of _VO2, which is lower than
the 3.5 mL/kg/min for people without disabilities in
the CPA (1 MET of CPA; p5 0.05). The means and
SDs of the group MET values in each PA selected
were computed and summarized in Table III.
The low intensity and unique activities satisfied
the expectations such that those activities were to
be classified as ABS or ADO. Even though it was
MET for paraplegia 339
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assumed that vacuuming and mopping would be
categorized as ABD, those activities were actually
categorized as ABS, z5 1.96. Only moving chairs
was classified as the expected ABD, z¼72.3. In
other words, MET of moving chairs (4.2 MET)
using the observed 1 MET was different from the
MET (6.0 MET) in the CPA. There was no
statistical difference (p4 0.05) of MET values
between groups (i.e. gender, completeness of lesions,
and levels of injury) after applying the Bonferroni
correction.
Discussion
To be able to apply the CPA to persons with dis-
abilities, a supplement targeting a specific disability
population must be developed. This study addressed
two critical issues in developing such a supplement,
i.e. whether the ‘1 MET’ value needs redefining for
the targeted population and how a PA can be
included in the supplement, directly from the CPA,
modified from the CPA or developed outside the
CPA. In this study, 1 MET of PP was determined
and the difference of MET values was examined
between the observed values and values from the
CPA. The observed MET values were classified into
three-categories for PP to be able to extend the
existing CPA [5]. For individuals with paraplegia,
the 3.5 mL/kg/min value of 1 MET is not appro-
priate. Instead, 1 MET for PP (1 MET of paraplegia
group) was 3.1 mL _VO2/kg/min; therefore, 1 MET
of PP is clearly different from the assumed value
based on persons without disabilities. As a result, the
Table II. Descriptive statistics by gender.
Variables
Total (n¼ 31) Male (n¼19) Female (n¼ 12)
M SD M SD M SD
Height (cm) 161.26 22.99 164.95 28.11 155.42 9.34
Weight (kg) 60.52 15.32 66.26 15.53 51.42 9.89**
Age (year) 24.16 6.25 22.53 4.40 26.75 7.92_VO2peak (mL) 1545.01 504.08 1806.12 457.61 1131.58 214.69***
_VO2peak (mL/kg) 25.87 6.32 27.96 6.29 22.56 4.98*
RMR EE (kcal/day) 1256.97 271.33 1392.47 232.62 1042.42 174.07***
RMR _VO2 (mL/kg/min) 3.13 0.54 3.20 0.62 3.02 0.37
Total fat mass (kg) 16.20 6.76 15.04 7.13 17.38 6.27
Total lean mass (kg) 42.82 12.02 49.49 9.98 32.80 6.69***
Total fat% 26.44 8.92 22.12 6.90 32.91 7.75**
M, mean; SD, standard deviation; RMR, resting metabolic rate; EE, energy expenditure; and total fat%, percent of total fat.
*p50.05, **p50.01, ***p5 0.001.
Table III. MET values and category of the activities.
METs calculated using
Category1 MET of individuals (I) 1 MET of CPA (P) METs
from CPA
(M) values
z scores
I vs. MActivity M SD M SD Expected Observed
1 1.3 0.2 1.1 0.3 1.5 ABS ABS 70.9
2 1.2 0.2 1.1 0.2 1.0 ABS ABS 0.9
3 1.3 0.3 1.1 0.3 1.8 ABS ABS 71.8
4 2.7 0.6 2.4 0.6 ADO ADO
5 3.3 0.5 2.9 0.5 3.5 ABD ABS* 70.4
6 3.9 0.7 3.5 0.8 3.5 ABD ABS* 0.6
7 4.2 0.8 3.7 0.9 6.0 ABD ABD{ 72.3{
8 4.4 1.3 3.9 1.3 ADO ADO
9 4.4 0.9 3.9 0.9 ADO ADO
10 5.8 0.9 5.1 1.1 ADO ADO
I¼MET values were calculated based on individual’s RMR mL _VO2/kg/min in this study.
P¼MET values were calculated based on 1MET from CPA, which is 3.5 mL _VO2/kg/min for able-bodied people.
M¼MET values from compendium of physical activity [5].
*difference between expected and observed categories.{z4 1.96.
ABS, activity by both able-bodied and disability populations with similar METs; ABD, activity by both able-bodied and disability
populations with different METs; ADO, activity by a targeted disability population only.
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EE of PP could be overestimated when using the 1
MET in the CPA (i.e. 3.5 mL/kg/min). Thus, the
subpopulation-specific 1 MET (3.1 mL of _VO2/kg/
min) should be used when estimating EE in people
with paraplegia.
Using participants’ own RMR, the MET values of
10 selected PA were calculated and then were
classified into one of three categories, ABS (i.e.
activity with similar METs for both able-bodied and
disability populations), ABD (i.e. activity with
different METs for able-bodied and disability
populations), and ADO (i.e. activity engaged only
by the targeted disability population). Five activities,
working on computer (1.3 MET), watching TV (1.2
MET), reading (1.3 MET), vacuuming (3.3 MET),
and mopping (3.9 MET) were classified as ABS.
Only the activity of moving chairs (4.2 MET) was
classified as ABD, which means the MET value of
this activity was different from the MET from the
CPA for people without disabilities. Wheelchair
pushing activities were classified as ADO and their
MET values were 2.7 MET for pushing on a tile
floor, 4.4 MET for pushing on a sidewalk, and 4.4
MET for pushing on a ramp. Arm ergometer
exercise at 60 W (5.8 MET) was also classified as
ADO. These findings indicate that the CPA can be
extended and include MET values of unique
activities engaged in by PP. The four-categories of
PA, i.e. AAO, ABS, ABD, and ADO, proposed
in this study provided a useful framework for
identifying and selecting PA for future supplement
development.
There were two other interesting findings of this
study. First, no statistical difference in MET values
was found between injury levels or completeness of
lesion. In a previous study [10], RMR and total
energy expenditure (TEE) of PP were different
depending on the completeness of lesion; for
instance, 10 persons with incomplete SCI
(2582+ 852 kcal/day) showed higher TEE than 18
persons with complete paraplegia (2072+ 505 kcal/
day). This could be caused by the lower level of
injury level (S4–5) compared to this study (T3-L
level). Surprisingly, many studies have been con-
ducted to compare _VO2 peak between different levels
of injury or completeness of lesions at T3-L level, but
a few studies have investigated the impact of injury
levels or completeness of lesions on TEE [10,11,
26,27]. Therefore, to examine the impact of injury
level and completeness of lesions on TEE more
studies are needed. Another possibility for the ‘no
difference’ result could be the intensity level of the
activities. Most of the previous studies [28–30]
employed _VO2 peak, as a high-intensity measure, as
the dependent variable, in the laboratory settings to
examine the group differences. In contrast, most of
the PAs employed in this study were of low-intensity
of common daily activities, which may not easily
discriminate the difference between the injury level
and completeness of lesions. Because MET values,
on the other hand, are commonly used as a
‘universal’ standardized unit, no group difference
could be helpful to develop the supplement of CPA
quicker for PP without considering the group
differences.
The second interesting finding is related to the
intensity level for PP. In the CPA, the activity of
moving chairs was expected to be a vigorous activity
(46.0 MET). However, actual MET value of this
activity is only 4.2 MET, which makes it a moderate
activity for people with paraplegia and put it into the
ABD category. Arm ergometer exercise at 60 W (5.8
MET) was also determined as a moderate activity
(MET�3 and�6) because it was short of the 6 MET
level needed to meet the definition of a vigorous
activity. According to the cut off of PA intensity using
oxygen consumption [4], vigorous activities (46
MET) are classified when maximal oxygen consump-
tion is 460% and moderate PA (�3 and�6 of MET)
is classified when it is defined at 40–59% of _VO2 peak.
Interestingly, in this study, arm ergometry exercise at
60 W elicited a mean of 69% of _VO2 peak (25.87 mL/
kg), 61% for males (27.96 mL/kg), and 83% for
females (22.56 mL/kg). Therefore, the difference of
the intensity of MET value is likely due to the relatively
low _VO2 peak of the individuals with paraplegia in this
study, suggesting that MET levels alone may not be an
appropriate way to describe the intensity of the activity
for persons with PP.
Finally, three limitations of this study should be
acknowledged. First, because we did not include
individuals with tetraplegia, the finding of this study
can only apply to PP. Second, all PA were performed
by PP who use self-propel wheelchair. It is a well-
known fact that many PP now use electric powered
wheelchairs or partially power-assisted wheelchairs
(e.g. pushrim-activated power-assisted wheelchairs;
PAPAW, [31]). In fact, the power-assisted wheel-
chairs have been found to be helpful for transfer and
to travel easily [32,33] with less pain, EE, and upper-
body extremity of motion compared with the self-
propel or manual wheelchairs. Therefore, it is
expected that the usage of this kind of partially
power-assisted wheelchairs will get more popular.
Because EE will be significantly reduced when using
powered or partially powered wheelchairs, the MET
values reported in this study should not be directly
applied to the users of these wheelchairs. The
adjustment for the MET values generated from
manual wheelchair studies is needed.
The third limitation of this study is that the impact
of individual variability on MET value estimation
was not investigated. Using the mean of individual
MET values, the MET value of a specific of PA is
MET for paraplegia 341
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determined. Although this group calibration practice
is a well accepted practice, it may not be appro-
priated for persons with disabilities due to their
known large variability [34,35]. One way to correct
the error of the group calibration is to employ
individual calibration, i.e. use one person’s own
MET values for prediction. In fact, individual
calibrations have been used in measuring PA and
related EE [36–38]. The cost of such a practice,
however, could be too high. Studies are needed to
determine the degree of errors when employing the
group calibration and accuracy improvement when
employing the individual calibration and associated
cost.
Conclusion
One MET for PP is 3.1 mL/kg/min, which is
different from that of CPA (3.5 mL/kg/min). The
MET values listed in CPA were also found different
from the ones observed from PP. These findings
confirmed that to be able to extend CPA to persons
with disabilities, the supplements that have
taken targeted subpopulations’ EE characteristics
and the types of activities they engaged into the
consideration must be constructed. Future studies
should include individuals with tetraplegia, examine
the difference between manual and powered wheel-
chairs users, and determine the impact of individual
variability.
Acknowledgments
We appreciate the tremendous help and support of
Drs. Kenneth Pitetti, Kyle Ebersole, Ellen Evans,
and Ms. Daina Mallard. This study was supported
by the Carl V. Gisolfi Memorial Research Fund from
the American College of Sports Medicine (ACSM)
Foundation and a Schneider Research Award,
College of Applied Sciences, University of Illinois
at Urbana-Champaign. The results of this study do
not constitute endorsement by ACSM.
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