Exercise Intensity During Power Wheelchair Soccer
J.P. Barﬁeld, DA,
Laura Newsome, PhD,
Laurie A. Malone, PhD
Department of Health and Human Performance, Radford University, Radford, VA; and
Alabama-Birmingham/Lakeshore Research Collaborative, Birmingham, AL.
Objective: To determine exercise intensity during power wheelchair soccer among a sample of persons with mobility impairments.
Design: Cross-sectional descriptive.
Setting: On-site training facilities of multiple power wheelchair soccer teams.
Participants: Participants with severe mobility impairments (NZ30) (mean SD, age: 29.4015.51y, body mass index: 24.116.47kg/m
power soccer experience: 7.913.93y, disability sport experience: 12.449.73y) were recruited from multiple power wheelchair soccer teams.
Interventions: Portable metabolic carts were used to collect oxygen consumption (
) data during resting and game play conditions.
Main Outcome Measures: Average
(expressed in metabolic equivalent tasks [METs]) during resting and game play conditions and rating of
perceived exertion for game play.
increased from 1.350.47 METs at rest to 1.810.65 METs during game play. This 34% increase in exercise intensity was
signiﬁcant (P<.01) and supported by a mean perceived exertion score of approximately 13 (somewhat hard).
Conclusions: Although not able to sustain an intensity associated with reduced secondary disease risk (ie, 3 METs), the documented light-
intensity exercise in the current study surpassed an intensity threshold associated with improved functional capacity and performance of daily
living activities (ie, 1.5 METs).
Archives of Physical Medicine and Rehabilitation 2016;-:-------
ª2016 by the American Congress of Rehabilitation Medicine
Since the classic studies of Blair and Brodney
research has consistently shown the relationship between
activity-based energy expenditure and reduced risk for chronic
mortality and morbidity. Although this behavioral risk reduction
balance is important to the general population, it becomes even
more essential to persons with disabilities. Disability refers to an
impairment that limits 1 or more activities of daily living.
Unfortunately, persons with disabilities, in particular physical
disabilities, are less likely to engage in healthy physical activity
behavior compared with persons without disabilities.
result, this population not only faces morbidity concerns with their
primary disability, but also secondary disease risk (eg, coronary
artery disease and obesity) becomes profound.
Fortunately, exercise and physical activity behavior have
multiple beneﬁcial outcomes for persons with physical disabil-
ities. Similar to the general population, regular physical activity
among persons with physical disabilities results in improved
improved lipid proﬁles,
enhanced vascular func-
and reduced chronic disease risk.
For these beneﬁts to
occur, the activity or exercise has to be a regular part of one’s
lifestyle and must be sustained at a speciﬁc intensity. The intensity
threshold for the aforementioned health beneﬁts is considered
moderate-intensity exercise and can be quantiﬁed as 3 metabolic
equivalent tasks (METs) or, stated differently, an exercise intensity
that is 3 times the energy expenditure at rest.
However, persons with physical disabilities, especially those
with mobility impairments, are more likely to engage in light-
intensity exercise, an effort that falls below the 3-MET
Light-intensity exercise has important beneﬁts to
persons with mobility impairments, including maintenance of
functional capacity or the ability to complete everyday tasks.
For example, a lifestyle that includes light-intensity physical
activity results in improved wheelchair mobility,
and enhanced life satisfac-
Although there is debate as to the exact intensity range and
minimum threshold for a behavior to be considered light-intensity
exercise, 1.5 METs is the criteria most often reported as the
Supported by a SEED Grant from the Sponsored Research and Grants Management Depart-
ment of Radford University.
0003-9993/16/$36 - see front matter ª2016 by the American Congress of Rehabilitation Medicine
FLA 5.4.0 DTD YAPMR56572_proof 23 July 2016 1:53 pm ce
Archives of Physical Medicine and Rehabilitation
journal homepage: www.archives-pmr.org
Archives of Physical Medicine and Rehabilitation 2016;-:-------
threshold that distinguishes light-intensity exercise from sedentary
behavior (<1.5 METs).
This threshold is an important marker
for persons with mobility impairments because the ability to engage
in light-intensity exercise above 1.5 METs reduces func-
Wheelchair sport as exercise
Increased popularity of disability sport is now exposing more
persons with mobility impairments, especially manual wheel-
chair users, to the protective effects and functional beneﬁts
of regular physical activity. Disability sport is a meaningful
rehabilitation and postrehabilitation physical activity option
and, unlike able-bodied sport, provides greater participation
opportunities as people age.
Sport can be an effective
exercise mode because it has the ability to improve both func-
tional capacity and quality of life.
Functional capacity, or
the ability to do work such as activities of daily living, is un-
questionably enhanced through sport-based ﬁtness improve-
Additionally, quality of life gains are realized through a
variety of mechanisms including enhanced personal relation-
improved self-care skills, and acceptance of
However, the exercise stimulus or demand
varies with each sport, yielding different exercise intensities
during game play that, in turn, yield varied chronic adaptations.
To identify the potential health or functional outcomes of regular
participation in any sport, it is essential to determine the
activity-based exercise intensity for each.
Although there are not an extensive amount of exercise
intensity studies on manual wheelchair sport, the initial efforts
show sustained moderate-intensity exercise across a variety of
competitive sports. Wheelchair basketball has 1 of the highest
activity-based energy demands, resulting in intensities between 4
and 8 METs.
Wheelchair tennis, despite the individual nature
of the sport, does not pose as high a demand. However, sustained
intensities of 3.5e6 METs have been consistently reported.
Energy expenditure has also been examined in wheelchair
rugby, and because of the reduced active muscle mass in these
athletes (ie, players with tetraplegia), sustained energy expendi-
ture appears to be close to the moderate-intensity threshold,
namely 3 METs.
Interestingly, exercise intensity sustained dur-
ing certain active video games appears to be consistent with some
manual wheelchair sports. Sustained intensities of 3e5 METs
have been shown across games such as Wii boxing,
and Dance Dance Revolution.
Although one might expect
expenditure during video game play to be lower than the actual
sport, one must remember that the shoulders and upper limbs
serve as the prime movers for both modes of activity. Based on
these initial studies of wheelchair sport, it is clear that certain
sports can meet the threshold for health (3.0 METs) and functional
(1.5 METs) beneﬁts.
Power wheelchair soccer
Power wheelchair soccer is a sanctioned sport for persons with
the most severe mobility impairments. Persons who rely on
power wheelchairs have limited sport/activity opportunities and
are therefore at great risk for a sedentary lifestyle and associated
The sport of power wheelchair soccer requires all
players to use a motorized or electric wheelchair for ambulation,
seemly removing the potential for exercise stress. However,
players have reported perceived exercise efforts during partici-
(ie, participants reported feeling fatigued and tired
after competition, which are typical responses to an exercise
stimulus). Although unexpected, this outcome may be supported
by acute physiological responses demonstrated during activity.
An initial physiological study on power wheelchair soccer
reported that 71% of participants were able to sustain 55% of
maximum heart rate across an entire match.
response would meet a moderate-intensity threshold; however,
the study did not control for endocrine contributions to the
response. Therefore, it is not clear if the acute heart rate increase
was caused by exercise stress or an elevated hormonal response
to game play.
If exercise stress is demonstrated during power wheelchair
soccer, this sport may be an effective therapeutic modality to
reduce morbidity risk (3 METs) or improve functional capacity
(1.5 METs) among persons with profound mobility impair-
This possibility would be a meaningful outcome
to therapists, physicians, and participants because few physical
activity opportunities exist for power wheelchair users.
Individuals dependent on electric wheelchairs face the greatest
environmental and social barriers to physical activity, and the
need to examine the potential beneﬁts of a viable sport option is
warranted. To determine if power wheelchair soccer exceeds
either a light- or moderate-intensity threshold, it is necessary to
assess exercise intensity during actual participation. Therefore,
the purpose of this study was to determine the exercise intensity
during power wheelchair soccer activity. Our hypothesis,
based on previous studies examining acute responses to power
wheelchair soccer, was that participants would sustain light-
intensity, if not moderate-intensity, exercise during power
Participants (NZ30) were recruited from 13 regional teams from
the Midwestern, Northeastern, and Southeastern United States. A
description of the project was forwarded to players through team
coaches, but individuals had the option to participate so that there
was no coercion. A convenience sample of approximately 2e3of
each team’s athletes chose to participate within 1 month of
recruitment and consisted primarily of players who were male
(nZ21, 70%) and white (nZ25, 83%). Being a member of a US
Power Soccer Association team was the only eligibility criterion.
Typical of power wheelchair soccer athletes, participants had a
wide range of ages and experience levels (table 1). Power
wheelchair soccer was the only adaptive sport experience among
the majority of participants (nZ18, 60%); however, the partici-
pants’ average of 7 years of power wheelchair soccer experience
shows the veteran status of the group. The participant sample
List of abbreviations:
CP cerebral palsy
MD muscular dystrophy
MET metabolic equivalent task
RPE rating of perceived exertion
SCI spinal cord injury
SMA spinal muscular atrophy
2 J.P. Barﬁeld et al
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consisted of persons with amputations (nZ1), arthrogryposis
(nZ3), cerebral palsy (CP) (nZ6), spinal muscular atrophy
(SMA) (nZ11), other types of muscular dystrophy (MD) (nZ4),
spinal cord injury (SCI) (nZ4), and traumatic brain injury (nZ1).
Institutional review board approval was obtained before the study,
and all players were required to provide informed consent or
assent with corresponding parent consent before participation.
Exercise intensity was assessed with 2 instruments. A subjective
assessment of exercise intensity was measured with Borg’s 6 to
20 rating of perceived exertion (RPE) scale. The RPE scale
has been used as a valid assessment of effort in the sample
populations, speciﬁcally in persons with CP,
The scale criterion associated with light-intensity exercise in the
general population is a score of 11 (fairly light), and the criteria
associated with moderate-intensity exercise is a score of 12e13
An objective assessment of exercise intensity was measured
using 1 of 2 telemetric portable gas analyzers (K4 b2
). The analyzers were powered 30 minutes before testing
and calibrated according to the instruction manual with gases of
known concentration (16% O
and 4% CO
) before each test day.
Each system was secured to the upper chest with a harness in a
position to minimize impact on movement of the participant. A
ﬂow sensor unit was connected to a face mask ﬁtted over the
participants’ mouth and nose (Hans Rudolph ﬂow sensor
units detect airﬂow by the rotation of a low-resistance turbine.
Studies have shown both K4 b2 and Oxycon Mobile to be
valid and reliable systems for the measurement of respiration
These systems measure the volume of oxygen
) during activity, which is an objective measure
of exercise intensity.
can be reported in multiple units, and
we chose to report units in METs so that we could compare
sustained power wheelchair soccer intensity against the 1.5- and
3.0-MET thresholds of light-intensity and moderate-intensity
was measured breath by breath with
Data were collected during regularly scheduled power wheelchair
soccer practices or games. Power wheelchair soccer is played in
two 20-minute continuous-play halves; therefore, we delimited
assessment to continuous game play conditions rather than drill
activity that included stoppage time for coach instruction. At the
start of a practice or game, researchers ﬁtted 1e2 participants
with a portable metabolic analyzer and recorded
data were converted to METs using a denominator
of 3.5, with the exception of persons with SCI, in which case 2.7
was used to adjust for reduced fat-free muscle mass because of
atrophy in this population.
All recordings were made while the
participant was in his or her game chair, and the portable
equipment was a successful instrument option because players
were able to participate without interruption of data collection or
actual game play. METs were measured over 5 minutes of rest
and at least 10 minutes of continuous game play activity with the
average of 30-second scores reﬂecting each condition score.
These time frames were selected because they have been used
previously to collect steady-state exercise intensity data, specif-
, for the sample population.
Also, the ﬁrst 30 sec-
onds of game play was excluded from analyses so that
participants had time to acclimate to the new stage.
assessed at the conclusion of at least 10 minutes of continuous
During practices, game play data were collected on 2 players at
a time during interteam scrimmages (1 player from each team).
Scrimmages typically lasted 10e15 consecutive minutes without
stoppage in play. This time limit was imposed because of the need
for teams to work on other activities within the given practice
time. We collected scores on a regulation power wheelchair soccer
court at 3 distinct practice sites (1 rehabilitation facility, 1 church
gym, and 1 school gym). Data were collected within a 2-day
period at each facility in March, April, and June 2015. Data from
16 independent participants, using both gas analyzers, were
collected during practice conditions. During games, game play
data were collected on 1 player at a time during each game half.
Halves lasted 20 consecutive minutes without stoppage in play.
We aligned testing around conference league play so that we again
collected data within a 2-day period (November 2015) on a
regulation court at an alternative rehabilitation facility. Data from
14 independent participants, using only the K4 b2 unit, were
collected during power wheelchair soccer games.
Although data collection delimited to 1 setting or the other would
have enhanced the internal validity of the study, the dual collection
settings enabled us to double our anticipated sample size, maxi-
mizing the external validity of the current ﬁndings. This point is
important because, despite the growth in power wheelchair soccer, it
is difﬁcult to recruit multiple players in any given region, requiring
data collection at multiteam sites. A sample size of 10 participants
was needed to detect a mean increase from 1.0e1.5 METs with 80%
power (http://biomath.info/power/prt.htm). Although 16 partici-
pants were initially recruited, we did not have at least 10 persons
with the same type of physical disability. Fortunately, the ability to
collect data on regulation courts under similar continuous game play
conditions at each facility within 2-day sessions eliminated poten-
tial bias caused by possible seasonal variation or training effects
Because we collected data in 2 settings with 2 gas analyzers, our
ﬁrst priority was to ensure that data should be grouped together for
analyses. We conducted independent group ttests on mean rest,
game play, and RPE scores to ensure no signiﬁcant differences
existed between metabolic units or between practice and game
Table 1 Participant demographics
Descriptive Variables Mean SD Range
Age (y) 29.4015.51 7.00e63.00
Height (cm) 162.7915.20 109.00e187.96
Weight (kg) 63.9119.55 27.21e105.20
Body mass index 24.116.47 12.03e39.56
Years in power soccer 7.913.93 0.33e15.00
Years in disability sport 12.449.73 0.33e40.00
Exercise intensity power soccer 3
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Mean METs and RPE were computed for game play to determine if
power wheelchair soccer participants sustained light- or moderate-
intensity exercise during game play. A repeated measures ttest was
conducted on METs to determine if exercise intensity increased
signiﬁcantly from 5 minutes of rest (P<.05). SPSS 22.0
for Mac was
used to analyze all descriptive and inferential statistics. Addition-
ally, we visually inspected scores of players to examine the potential
of disability type to inﬂuence acute responses.
Each participant had a complete data set with the exception of 1
practice player missing the 5-minute rest period (because of time
limitation). No signiﬁcant mean differences existed between gas
analyzers or practice/game participants on mean rest, game play,
or RPE (P>.05) (table 2); therefore, all data were analyzed
collectively as 1 sample (NZ30). Regarding exercise intensity,
participants demonstrated light-intensity exercise, but not
moderate-intensity exercise, during game play conditions while
using a motorized wheelchair (see table 2). Energy expenditure
increased by 34% from the rest period to game play, and this
increase was signiﬁcant (P<.01). This increase in energy expen-
diture was supported by a mean RPE score of 12.8 after game play
conditions. This perceptual effort score is evaluated as somewhat
hard on the Borg scale.
Twenty of the 30 participants sustained light-intensity exercise
across 10 minutes of power wheelchair soccer activity (ie, 1.5
METs). Although insufﬁcientstatistical power prevented analysesof
subgroups, visual inspection of data did not support disability type as
a discriminating variable between persons who did and did not sus-
tain light-intensity exercise. The majority of participants with each
type of mobility impairment sustained light-intensity exercise;
however, there was at least 1 player with each disability who did not.
In general, athletes with mobility impairments are capable of
sustaining vigorous-intensity exercise (>6 METs) during manual
However, the current population has the
greatest physical challenge to voluntary exercise and, by partici-
pating in power wheelchair soccer, are unable to pursue manual
wheelchair sport options that result in vigorous-intensity exercise.
The purpose of this study was to determine the actual exercise
intensity during power wheelchair soccer, and participants
sustained 1.8 METs or light-intensity exercise across 10 minutes
of game play. Although this intensity does not meet the 3.0-MET
threshold associated with reduced chronic disease risk, the ability
to surpass and sustain 1.5 METs shows exercise stress during
power wheelchair soccer associated with functional beneﬁts. The
objective response to power wheelchair soccer was conﬁrmed by a
perceived increase in effort, with participants ranking game play
as somewhat hard. The current ﬁndings identify the ability of
most, but not all, players to sustain light-intensity exercise while
using a power wheelchair.
Comparison to power wheelchair soccer research
The current ﬁndings are consistent with initial research into power
wheelchair soccer. Barﬁeld et al
reported that 71% of athletes
with CP and MD sustained moderate-intensity heart rates during
power wheelchair soccer matches. Heart rate can be inﬂuenced by
mechanisms associated with physical disability (eg, cocontraction
and increased muscle tone); therefore, the direct assessment of
energy expenditure in the current study is likely a more accurate
measure of exercise intensity. Regardless, our ﬁndings and those
reported by Barﬁeld reﬂect sustained exercise stress during game
play. This ﬁnding is further supported by an increase in energy
expenditure from the rest period to drill conditions and drill to
game play followed by a decrease in exercise intensity during
cooldown activities during practice sessions (data not reported).
Even with only a few empirical studies on power wheelchair
soccer, early evidence supports the ability of players to sustain
The aforementioned physiological data reﬂect the objective
exercise stress during power wheelchair soccer reported on 2
distinct samples. Jeffress
conducted a longitudinal study of 35
power wheelchair soccer participants and identiﬁed exercise
fatigue as a major theme from qualitative responses. His sample
participants repeatedly stressed that power wheelchair soccer was
tiring because of its exercise effect. Perceived exertion was also
reported among a smaller sample (NZ25) of power wheelchair
These athletes reported that exercise (ie, power
wheelchair soccer) was difﬁcult and a major barrier to regular
physical activity. The increase in RPE to somewhat hard in the
current study supports the affective perceptions from both
Comparison to alternative physical activities
The exercise intensity sustained in the current study is consistent
with a number of functional tasks listed in the compendium of
physical activities including bathing, eating, and washing dishes.
In essence, power wheelchair soccer energy expenditure surpassed
the 1.5-MET threshold for sedentary activity and is comparable
with a number of basic activities of daily living.
light-intensity activity may not have the same health beneﬁts as
sustained moderate-intensity exercise, power wheelchair soccer
requires energy expenditure consistent with everyday self-care
activities reported for the general population. Based on the prin-
ciple of use/disuse, this activity may contribute to increased
longevity of independence and self-care skills. However, caution
is warranted with this assumption because energy expenditure
estimates in the compendium have yet to be validated for varied
populations with mobility impairments.
In addition to functional activities, the acute response in the
current study is similar to the 1.83e2.7 METs reported during
circuit training in manual wheelchair users with SCI.
Table 2 Exercise intensity during power soccer game play
Conditions n Rest METs Game play METs RPE*
Unit 1 8 1.360.51 1.820.72 12.883.53
Unit 2 24 1.320.39 1.760.78 12.632.13
Practice 16 1.290.38 1.830.55 12.332.77
Tournament 14 1.410.56 1.780.76 13.423.26
Sample 30 1.350.47 1.810.65 12.803.11
NOTE. Values are mean SD.
* Borg RPE scale (6e20).
4 J.P. Barﬁeld et al
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difﬁcult to speculate as to how power wheelchair activity may
approximate manual wheelchair intensity, but the need to
compensate for atypical muscle tone and involuntary muscle
activity may contribute, at least among players with CP.
need to maintain balance while in the chair, the need to generate
isometric contractions to receive impact, or the need to decelerate
the body after an abrupt spin or stop may also account for some of
the increased energy expenditure during power wheelchair soccer.
The mechanisms that explain the actual intensity increase from the
5-minute rest period need further investigation.
Evaluation by participant group
Although statistical power was lacking to analyze each group,
visual inspection of individual data revealed 2 important ﬁnd-
ings in this study. The primary ﬁnding is that the majority of
participants sustained light- or moderate-intensity exercise
during power wheelchair soccer (nZ20, 67%). At least two-
thirds of players within each disability group surpassed 1.5
METs during game play, with the exception being the double
amputee and athletes with a particular form of MD, namely
SMA (only 55% of these players sustained >1.5 METs). This
outcome highlights the potential of power wheelchair soccer to
serve as an exercise or rehabilitation mode for participants with
a variety of mobility impairments. The second important
outcome is that disability group did not distinguish responders
from nonresponders. In other words, disability group itself did
not distinguish those who sustained light-intensity exercise and
those who did not. Although the subsamples are too small to
draw conclusions, the majority of participants with each type of
disability were able to sustain 1.5 METs during game play
including individuals with arthrogryposis (2/3), CP (5/6), MD
other than SMA (3/4), SCI (3/4), and SMA (6/11). This ﬁnding
has important applications to rehabilitation and therapeutic
exercise prescription because questions remain as to which
factors distinguish persons able to sustain light-intensity exer-
cise during power wheelchair soccer (ie, responders) and those
who are not (ie, nonresponders).
Measuring exercise intensity
Although there are multiple ways to examine the exercise in-
tensity of a sport (or energy demand for a given sport), we chose
expressed as METs (1 METZ3.5 mL$kg
is a better option than heart rate in this
sample because persons with mobility impairments can have
either blunted or accelerated heart rate responses to aerobic and
muscular work, making estimates of actual intensity unreliable.
This consideration is especially true for persons with CP
However, METs can be used to determine light- and
moderate-intensity thresholds as well as to compare against
established activities on various compendiums.
and 3.0 METs may be a meaningful threshold to scientists and
practitioners, a comparison of power wheelchair soccer with
similar compendium activities and self-care skills may be more
meaningful to participants and caregivers.
The major limitation in the current study is the heterogeneous
sample. Caution is warranted when extrapolating these results
because physiological responses can vary within and across
disability types. To address this limitation, we recruited a large
sample size. As a result, the sample ﬁndings are robust, less
likely affected by 1 particular group or disability. We maximized
sample size by collecting data under both interteam scrimmages
and conference games. These conditions were synonymous
because both offered continuous game play against an opponent
with no stoppage time. Regardless, future research must test
current ﬁndings against larger samples of stratiﬁed mobility
impairment groups (nZ10 per group). A second limitation is
that data were collected on-site. This design prevented the
researchers from assessing true resting
; therefore, scores
during the 5-minute rest period are likely higher than actual
resting intensity. To reduce the impact of this limitation, we
determined METs with a denominator of 3.5 (or 2.7 for persons
with SCI) rather than actual resting values. Future research
should assess true resting energy expenditure so that MET values
are relative to actual resting values.
It is worth noting that one should not necessarily use the current
MET values to determine calorie needs. Although assessment of
a valid assessment of energy expenditure, individuals with SPI and CP
may have an altered basal metabolic rate, rendering the use of METs
less useful for energy need usage.
Also, the use of RPE may, ulti-
mately, be a more practical mechanism to estimate energy expenditure
(exercise intensity) during disability sport.
Future research should
investigate the suitability of RPE to determine energy expenditure in
power wheelchair soccer. Finally, our study did not identify mecha-
nisms that distinguished responders from nonresponders. Future
studies on identifying mechanisms that allow players to reach light-
intensity exercise during power wheelchair soccer are needed.
In conclusion, persons with mobility impairments demonstrated
light-intensity exercise during power wheelchair soccer. This
objective assessment was supported by the perceived somewhat
hard effort reported by participants during game play. Although
the threshold may not be sufﬁcient to decrease morbidity risk
(ie, <3.0 METs), the sustained energy expenditure was consistent
with intensities sufﬁcient to enhance functional capacity and
performance of daily living activities (ie, 1.5 METs). The external
validity of the current ﬁndings seems strong because the sample
size (NZ30) had adequate power, and the acute responses were
similar across players with different disability types and varied
game play conditions.
a. Wii boxing and tennis; Nintendo.
b. Dance Dance Revolution; Konami.
c. K4 b2 Portable metabolic cart; Cosmed.
d. Oxycon Mobile metabolic cart; Care Fusion Respiratory Care.
e. Hans Rudolph ﬂow sensor; Hans Rudolph, Inc.
f. SPSS 22.0; IBM.
Cerebral palsy; Muscular atrophy, spinal; Muscular dystrophies;
Rehabilitation; Spinal cord injuries
Exercise intensity power soccer 5
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J.P. Barﬁeld, DA, Box 6957, Radford University, Radford,
VA 24142. E-mail address: abarﬁeld@radford.edu.
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