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ASSISTIVE TEC HNOLOGY
A comparison of functional mobility in standard
vs. ultralight wheelchairs as measured by
performance on a community obstacle course
HELEN ROGERS*, SEAN BERMAN, DENNIS FAILS and
JOUMANA JASER
Department of Physical Therapy, School of Allied Health Sciences, The University of Texas
Medical Branch, Galveston, Texas, USA
Accepted for publication: May 2003
Abstract
Purpose: Appropriate wheelchair prescription requires max-
imizing user function while justifying cost. The purpose of this
study was to investigate differences in a user’s performance of
mobility skills (on a community obstacle course) between an
ultralight (UWC) and standard wheelchair (SWC).
Subjects: Sixty healthy adults (mean = 28.3 years) without
wheelchair experience performed one course trial.
Methods: Participants were randomly assigned to an UWC or
a SWC. Researchers recorded time for completion, Rating of
Perceived Exertion (RPE), and number, location, and types of
errors committed. Errors included contact of WC and any
obstacle, front casters leaving the ground, or loss of directional
control (veering).
Results: A MANOVA of the data ( p 5 0.05) showed a
significant difference in numbers of contact errors (higher in
the SWC) and castor errors (higher in the UWC) between the
two wheelchairs. Number of veering errors, time to complete,
and RPE were not significantly different.
Conclusions: Differences in wheelchair design can lead to
differences in a user’s performance of functional mobility
skills. Choice of wheelchair may affect a user’s ability to be
independent in a community setting.
Introduction
A major dilemma for physical rehabilitation profes-
sionals in today’s dynamic health care system is provid-
ing a wheelchair prescription that maximizes an
individual’s function and independence and justifies
the cost.
1, 2
Many third party payers have been reluctant
to reimburse for ‘sports’ or ultra-light wheelchairs
(UWCs) due to higher costs and perceptions that UWCs
are suitable only for wheelchair athletes.
3
However,
because clinicians perceive that the unique modifications
offered by these chairs allow for increased mobility,
ultra-light wheelchairs are frequently being recom-
mended for individuals who are not athletes.
1
Research
has demonstrated that changes in the design of a wheel-
chair results in positive changes in energy cost, joint
kinematics and propulsion biomechanics. In general,
the design of the UWC places the axle forward of the
centre of gravity of the user. This has been shown to
decrease rolling resistance and increase propulsion effi-
ciency
4
as well as decreasing upper extremity electro-
myogram (EMG) readings and increasing the
smoothness of pro pulsion.
5
Also, the ability to adjust
the seat height of the UWC in relation to axle position
has been shown to have positive effects on cardiovascu-
lar parameters, energy cost, and propulsion technique;
all of which can improve propulsion biomechanics.
6
Yet most wheelchairs covered by Medicare or other
third party payers have a standard design with non-
adjustable rear axles placed posterior to the user’s center
of gravity and fixed seat positions.
7
New design techniques, materials, and engineer ing
have not only made wheelchairs lighter, but also more
durable, adjustable, and maneuverable.
1, 8–11
However,
there is little published evidence to demonstrate that
differences in wheelchair design produce difference in
the functional mobility of the user in the community
setting. Currently, 96.2% of wheelchair users in the
USA have some degree of functional limitation and
85.7% are unable to perform one or more of the eight
* Author for correspondence; Helen Rogers PT, MA,
Department of Physical Therapy, School of Allied Health
Sciences, UTMB, 301 University Blvd., Route 1144, Galves-
ton, Texas, 77555-1144, USA. e-mail: hrogers@utmb.edu
DISABILITY AND REHABILITATION, 2003; VOL.25,NO. 19, 1083–1088
Disability and Rehabilitation ISSN 0963–8288 print/ISSN 1464–5165 online
#
2003 Taylor & Francis Ltd
http://www.tandf.co.uk/journals
DOI: 10.1080/0963828031000152048
mobility-related functions as defined by the National
Health Interview Survey on Disability (NHIS-D).
12
In
order to prescribe the optimal wheelchair, therapists
need to determine whether there is a baseline difference
in functional mobility at a community level that can be
attributed directly to the wheelchair’s design or config-
uration regardl ess of a users pathology or experience
level.
Until now, wheelchair research has primarily focused
on the metabolic cost,
13 – 15
joint kinematics
16 – 18
and
mechanical efficiency
6, 19 – 21
of specific wheelchair designs
or parameters. In addition, more clinically aimed wheel-
chair studies have looked at differences in metabolic
physiology/functional mobility in patients with identi-
fied pathologies, such as spinal cord injuries.
13, 22, 23
Only
a few studies have attempted to compare one wheelchair
design to another on parameters of function.
23, 24
Most
studies have investigated the effect on propulsion of
changing an individual parameter of a wheelchair, such
as degree of wheel camber or hand rim size, rather than
the effect of changes in overall wheelchair design. Final-
ly, no studies have examined functional mobility in a
community environment versus a laboratory or
controlled setting.
Several studies have looked at differences between
wheelchairs of different design in physiological para-
meters be tween subjects with a disability.
13, 22, 23
Two
studies, Parziale
22
and Beekman, Miller-Porter, and
Schoneberger,
23
both found differences between subjects
with paraplegia and those with tetraplegia but neither
study failed to conclusively attribute these differences
to the type of wheelchair as opposed to the level of the
subject’s lesion. Also, the propulsion tasks in these
studies were carried out in a controlled setting rather
than the community. Hilbers and White
13
found a differ-
ence between the wheelchairs on a controlled velocity
task as well, but with a very homogeneous group of
subjects, none of whom had lesions that involved the
upper extremities.
In a pilot study with able-bodied subjects emphasizing
the effect of wheelchair design on community function,
we determined that there was no significant difference
in time to complete task between a SWC and an UWC
when propelling up a ramp and through a door.
24
We
did, however, find that there were significantly more
errors committed when propelling the UWC through
the door.
Cooper and his team
8, 9, 11
have provided a database of
studies focusing on the durability and cost effectiveness
of depot (SWC), lightweight (LWC) and rehabilitation
(UWC) wheelchairs using the American National Stan-
dards Institute/Rehabilitation Engineering and Assistive
Technology Society of North America (ANSI/RESNA)
standards. They found that, of the three wheelchair
types, the UWC was the most durable and had the best
value over its life span. Their data indicated that the
UWCs lasted 13.2 times longer in fatigue tests and were
3.4 times cheaper to operate than the SWCs tested.
These investigators also commented on the high degree
of adjustability of the UWC and speculated that adjust-
ability can increase the mobility of the user and reduce
the risk of secondary injury or disability.
8, 9, 11
None of these studies can convincingly say that one
wheelchair design is significantly superior to another in
a community setting or that the wheelchair design can
influence function among individuals with varying types
of disability. This study was designed to investigate the
effect of wheelchair design on mobility in a community
setting separate from the effects of pathology or train-
ing. We used a post-test only control group design to
compare the performance of healthy adults using an
UWC and a SWC on an obstacle course in a community
setting. Performance variables included the time to
complete the course, number, location and type of
errors, and a perceived rating of exertion (RPE).
Subjects
We recruited 60 healthy adults who were novice
wheelchair users from a population of University of
Texas Medical Branch at Galveston employees, students
and family/friends of UTMB personnel using e-mail
broadcasts and flyers on campus. This study targeted
adults within an age range of 19 to 55; no attempt was
made to include elderly adults or children. We collected
a sample of convenience that included 29 males and 31
females with a mean age of 28.3 years (range = 20 –
47). Subjects were randomly assigned to propel either
the UWC (n = 29) or SWC (n = 31) through an obstacle
course. In an attempt to rule out a training effect, we
excluded applicants with more than 3 h of wheelchair
propulsion experience in the past 12 months.
Data collection and analysis
Prior to attempting the obstacle course, all subjects
completed a health screen to rule out any limitations
due to a history of cardio-respiratory or musculoskeletal
impairment involving the hands, arms, shoulders, back
or neck (appendix 1). Even though the risks of complet-
ing this study were minimal, exclusion criteria were strict
to prevent any adverse occurrence. An answer of ‘yes’ to
the presence of any coexisting medical condition (includ-
ing pregnancy) that might compromise a pe rson’s ability
H. Rogers et al.
1084
to propel a wheelchair with maximal effort served as a
criteria for exclusion from the study. Subjects were
informed of the possible health risks including hand blis-
ters, falls, and heat stress. Subjects wore gloves to
prevent blisters, and we fitted the wheelchairs with
anti-tip bars to prevent falls. The trials took place on
an outside obstacle course set on the UTMB campus.
Trials took place in the early morning during the
summer, and subjects were monitored closely for signs
of heat stress. The UTMB Institut ional Review Board
approved the study and exclusion criteria and all
subjects completed a written consent form.
Subjects were given a verbal description of the obsta-
cle course and the various obstacles they would
encounter prior to their first trial. The verbal instruc-
tions were scripted to assure consistency. The subjects
did not receive prompts during the trials except to
assure proper direction on the marked obstacle course.
We chose obstacles commonly encountered on our
campus and considered general to a community setting.
The obstacle course was 1578 feet in length and
included three separate ramps with an average rise to
run of 1 : 16 feet, two doorways of 35-inch width,
two standard 7-inch curb cuts each 85 inches in length,
a simulated elevator task, and a slalom course through
six cones set 7 feet apart. Subjects had to negotiate all
obstacles without help from the examiners or pe des-
trians and were not allowed to use their feet in any
way. We informed the subjects that they were being
timed but instructed them to move at a comfortable
pace because we were also examining other aspects of
wheelchair prop ulsion in addition to the time to
complete the course. Subjects were not given the defini-
tion of errors or informed that errors were being
counted.
Two researchers performed the data collection. One
researcher was responsible for counting errors and iden-
tifying error location while the other timed the trial and
maintained direction on the course. The same researcher
collected each type of data for each subject to assure
maximum inter-trial reliability. The researchers piloted
the course with five non-subject volunteers to reduce
any potential intra-rater variability. We documented
completion time, number of errors, and RPE (rate of
perceived exertion) for each subject as well as the type
of error (castor, contact and veering errors) and the
specific obstacle or position in the course where each
error occurred (doorway, ramps, curb cuts or straight-
aways). Castor errors were defined as loss of contact
between the wheelchair castors and the ground. Contact
errors occu rred when the wheelchair touched any archi-
tectural barriers. Veering errors involved loss of direc-
tional control of the wheelchair, for example, veering
off to one side of the sidewalk during propulsion.
We used a multivariate analysis of variance (MANO-
VA) to analyse the differences in the performance vari-
ables between the trials performed in the SWC and
those performed in the UWC. We analysed all data at
the 0.05 alpha level using SPSS (SPSS, Chicago, Ill.)
statistical software.
Results
Table 1 summarizes the means and standard devia-
tions (SDs) for errors by type (contact errors, castor
errors, veering errors), completion times, and RPEs for
each group. Table 2 identifies the means and SDs of
the types of errors made according to the geography
of the obstacle course (ramps, curbs, steering, and door
errors).
The MANOVA indicated an overall significant differ-
ence in functional mobility between the UWC and SWC
(Hotelling’s T
2
= 0.344, p = 0.006, power = 0.874). Post
hoc univariate analyses indicated significant differences
in the contact (p = 0.021) and castor (p = 0.001) errors
between the two chairs. The number of veering errors
(p = 0.968), RPE (p = 0.492), and completion time
(p = 0.084) did not differ significantly between the two
groups.
When errors were analysed according to location (i.e.,
ramps, curbs, straight aways, and doors), post hoc
univariate analyses indicated significant differences in
errors that occurred with ramps (p = 0.009) , curbs
Table 1 Mean and SD of errors by type, RPE, and completion time
Outcome variables
SWC
MEAN/SD
UWC
MEAN/SD
Univariate
analysis
Contact error 21.06/14.60 13.52/9.26 p = 0.021
Castor error 3.55/4.70 12.62/13.16 p = 0.001
Veering error 1.77/2.17 1.79/1.35 p = 0.968
RPE 5.68/1.89 5.38/1.40 p = 0.492
Completion time 10:19/3:41 8:45/3:10 p = 0.084
Significant at a = 0.05
Table 2 Mean and SD of errors by location
Location of errors
SWC
MEAN/SD
UWC
MEAN/SD
Univariate
analysis
Ramp 2.32/3.37 6.41/7.64 p = 0.009
Curb 1.81/2.64 3.45/3.19 p = 0.034
Steering (straight-away) 3.29/2.62 5.03/5.24 p = 0.105
Door 18.97/13.63 12.76/8.83 p = 0.042
Significant at a = 0.05
A comparison of functional mobility in standard vs. ultralight wheelchairs
1085
(p = 0.034), and doorways (p = 0.042). The incidence of
steering errors (p = 0.105) was similar between the two
wheelchairs.
Discussion
The results of this study indicate that there is a signif-
icant difference in the functional mobility of healthy
adults when using an UWC and a SWC. We attributed
this difference primarily to the number of contact errors
(highest for the SWC) and castor errors (highest for the
UWC). Veering errors were not different between
subjects who used the two wheel chair types, nor did they
differ on their completion times or RPE.
We believe that the significant errors (contact and
castor) are related to the wheel chair design. The SWC
is larger, longer (due to footrest position) and heavier
than the UWC. The increased number of contact errors
supports the supposition that the SWC would be more
difficult to manoeuver especially in narrow spaces or
areas with a greater number of architectural barriers.
Indeed, there were significantly more errors for the
SWC in the location of doorways. The UWC, due to
its forward axle position relative to the center of gravity
of the user, is less stable to the rear and tips more read-
ily.
7
This tendency, combined with the lighter weight of
the UWC, explains the increased caster errors noted for
the UWC; these errors seemed to be primarily associated
with manoeuvering on elevated surfaces such as ramps
and curb cuts. We belie ve the distribution of types of
errors to types of wheelchairs to be clinically significant,
as it appears that the types of errors noted in the UWC
are more easily corrected by user experience than those
of the SWC. The most impor tant factor in controlling
the attitude of the wheelchair around the axis of pitch
(i.e. controlling the ‘tippiness’ of the wheelchair) has
been found to be appropriate manipulation of the user’s
head and upper trunk segment around the center of
gravity.
4
This ability to move and alter the dist ribution
of body weight in relation to the axle is a learned skill.
Rodgers et al. found improvements in the biomechanical
efficiency of propulsion after train ing (including trunk
position).
25
Therefore the number of castor errors can
be affected by user experience as they learn to manipu-
late their body weight in relation to the wheelchair axle
and their own center of gravity. The contact errors
noted in the SWC, however, are due to aspects of the
chair design such as length, width and size that are not
easily affected by the user. Therefore, the UWC users
have more potential to improve fun ction and decrease
errors as their understanding of the biomechanical
advantages of the UWC improves. This improvement
may have a clinically significant effect on functional
propulsion as the user gains experience.
No significant difference was found between the
wheelchairs for veering errors or for RPE. We conclude
that this is due to the inexperience of the subjects.
Because the subjects were able-bodied adults with mini-
mal to no wheelchair experience, both wheelchairs
proved equally difficult to manage initially. Subjects
exhibited an equal amount of difficulty with steering
and propulsion regardless of wheelchair assignment
due to the novelty of the task. Efficiency with wheelchair
propulsion, however, has been shown to improve with
experience.
26
Studies have shown that wheelchair
propulsion differs between skilled and non-skilled users
in the parameters of work output, mechanical efficiency,
and efficiency of propulsion.
27 – 30
However, we also
believe that the potential to improve in wheelchair func-
tion is higher when using an UWC. The UWC has a rear
axle position and smaller shoulder-to-push rim distance
that has been correlated with better fun ctional perfor-
mance.
6
Studies have shown that as the centre of gravity
is moved in a direction rearward and downward relative
to the axle, the propulsion patterns exhibit improved
mechanical efficiency,
6, 31
lowered EMG readings and
improved biomechanics,
5, 7
and enhanced performance.
4
Because these features of the UWC may improve
propulsion style with training, the user may also experi-
ence relatively fewer errors and lower RPE ratings than
users of a SWC. This would translate into better func-
tional mobility in the community for the UWC user
than for the SWC user.
Although the difference in completion time on this
obstacle course was not statistically different between
the two wheelchair groups, the UWC group demon-
strated a mean speed that was 1 min 34 s faster than
the average SWC speed (SWC = 10 min 19 s,
UWC = 8 min 45 s). This may be clinically significant.
Considering that a long community distance could
require as much as 30 min to traverse, the UWC may
potentially reach the terminal point approximately
4 min faster. If UWC users become more proficient than
SWC users as speculated, this time difference could
reduce overall fatigue and musculoskeletal stress.
This study utilized a populati on of subjects without
physical disabilities. While this helped assure a ‘novice’
status with regards to wheelchair propulsion, we are
unable to address how performance on the obstacle
course might have been affected by experience. There-
fore, one must be cautious not to generalize the results
of this study to individuals with various types of physi-
cal disabilities or to individuals with wheelchair propul-
sion experience. Given the location of the obstacle
H. Rogers et al.
1086
course, this study may not generalize to significantly
different community environments, especially those in
hilly or very urban areas. Further research is needed
to further investigate the effect of wheelch air design on
functional performance, especially the performance of
experienced users who independently manage their
mobility in a community setting.
Conclusion
Novice wheelchair users who manoeuvered a commu-
nity-based obstacle course in UWCs had fewer mobility
errors and faster completion times than those who use
SWCs. This difference may be attributed to design para-
meters of the wheelchairs but is also likely to be dependent
on experience of the user. Further research is needed to
delineate factors inherent in the wheelchair design versus
performance variables attributed to the user in order to
improve wheelchair prescription, maximize functional
mobility in the community, and justify reimbursement.
Acknowledgements
We acknowledge Dr. Martha Hinman PT, EdD with gratitude for
her expertise and advice with editing.
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1087
Appendix 1
ID# _________
(1) Sex: Male & Female &
(2) Age: ____________________
(3) Have you been diagnosed with any of the following medical conditions or do you presently have any coexisting
medical conditions that might compromise your ability to propel a wheelchair with maximal effort?
Asthma Yes & No &
Uncontrolled Diabetes Yes & No &
Heart condition (i.e. murmur) Yes & No &
Neurological impairment Yes & No &
(i.e. balance or equilibrium problems)
Recent fracture or joint sprain Yes & No &
Limitation in joint range of motion Yes & No &
Back pain Yes & No &
Upper extremity tendonitis or overuse injury Yes & No &
Mental Disability (i.e. dementia) Yes & No &
Other (please list) Yes & No &
If you checked yes to any box, please give a brief explanation:
___________________________ ______________________________________________________________________
___________________________ ______________________________________________________________________
___________________________ ______________________________________________________________________
(4) Please estimate the amount of prior wheelchair experience you have had within the past year.
& 0 – 3 hours & 3 – 10 hours
& 10 – 20 hours &4 20 hours
(5) For female subjects only:
Are you pregnant? Yes & No &
H. Rogers et al.
1088
