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ADAPTED
PHYSICAL
ACTIVITY
QUARTERLY,
1989,6,
109-
Ergonomics
of
Wheelchair Design:
A^
Prerequisite for OptimumWheeling Conditions
Luc
H.V.
van der Woude, Dirk-Jan E.J. Veeger,
and Rients
H.
Rozendal
Free University, Amsterdam
A review of wheelchair research within the scope
of the wheelchair
as a means
of daily ambulation
is presented. The relevance of a combined biomechanical
and physiological research approach is advocated for enhancing the body ofknowledge
of wheelchair ergonomics,
that is, the wheelchairluserinteraction
in relation to aspects of vehicle mechanics and the user's physical condition.Results of experiments
regarding variations in the wheelchairluser interface
stress
the possibilities
of optimization
in terms of wheelchair
dimensions and
user characteristics.Analysis of propulsion technique is aimed at the within-cycle characteristics and the time-dependent organization of technique.Ergonomics is a fairly new area of research that has emerged as a postwar specialization of human and technical sciences. The essence of ergonomics is theoptimization
of human work conditions (devices, tools, work, environment) with
respect to the capabilities of the human being such that health, safety, comfort,and efficiency are improved. In this respect, rehabilitation engineering might beseen as a special form of ergonomics. The design of a tool or assistive deviceis aimed at the restoration of (a modality of) functions and subsequently atenhancing the quality of the client's daily life. In most instances the tool in thissense is merely an extension of the human being, aimed at communication orinteraction with the environment. The optimization or fine-tuning of the inter-action between device and client in terms of individual efficiency, comfort, safe-ty, and health is part of ergonomics. Given the specific disability related problems,one might argue that ergonomics within the area of rehabilitation engineeringis a special form of ergonomics. However, as in other areas of ergonomics, thesame philosophy is applicable and basic rules of optimization are observed. Fun-damental research is needed in order to establish a body of knowledge appropri-ate for specifying the effects of an impairment or disability (Feeney, 1987;Rohmert, 1979). This is illustrated in the review of the ergonomics of wheel-chair ambulation presented here.
Request reprints from Dr. Luc
H.V.
van der Woude, Dept. of Functional Anato-
my, Faculty of Human Movement Sciences, Free University, Van der Boechorststraat9,^ 1081BT Amsterdam, The Netherlands.
110
van
der Woude, Veeger, and Rozendal
The relevance of research of manual wheelchair propulsion from an ergo- nomics perspective was first recognized in Europe by the German group ofHildebrandt and Engel (Engel
&^
Henze, 1981,1982,1984; Engel
&^ Hildebrandt,
1971,1974,1978; Hildebrandt, Berendes,
&^
Kroeger, 1970; Voigt
&^ Bahn, 1969;
Voigt, Berendes,
&^
Bahn, 1968). More recent studies focusing on the physio-
logical evaluation of wheelchair designs were conducted by Parziale, Lee,Scararnuzzi,
and Calvin (1986), Woude, Groot, Hollander, Ingen Schenau, and
Rozendal(1986), Hilbers and White (1987), and Gangelhoff, Cordain, Tucker,and Sockler (1988). Mechanical efficiency and energy expenditure were studiedin relation to several specific wheelchair configuration features, such as seatposition (Brubaker, McClay,
&^
McLaurin, 1984; Brubaker
&^
McLaurin, 1982;
Engel, Neikes, Bennedik, Hildebrandt,
&^
Rode, 1976; Lesser, 1986),
lever length
and mechanical advantage in lever driven wheelchairs (Brubaker, 1984; Engelet al., 1976). Moreover, preliminary studies have been initiated into muscleactivity and force generation
in^ wheelchair ambulation
(Brubaker, 1984;
Brubaker
&^ McLaurin, 1982; Cerquiglini, Figura, Marchetti,
&^
Ricci, 1981; Lesser, 1986).
To date, attention has been focused predominantly on hand rim wheelchairs.Perhaps due to both the complexity of the wheelchairluser combination and thevariation in research methods (Dreissinger
&^
Londeree, 1982), no conclusive
ergonomic guidelines have been formulated aimed at high efficiency and lowenergy cost of locomotion, and implying an optimum fitting of the wheelchairto the user.
Rationale
Hand-rim wheelchair propulsion is a straining way of ambulation: high cardio-respiratory responses are seen at relatively low levels of power output (Brattgard,Grimby,
&^
H h k , 1970; Glaser, Simon-Harold,
Petrofsky,
Kahn,
&^
Suryaprasad,
Voigt
&^
Bahn, 1969; Voigt, Berendes,
&^
Hildebrandt, 1968). Some studies
stressed the low gross mechanical efficiency, rarely exceeding a value of 10%(Brattgard
et al., 1970;
Brubaker
&^ McLaurin, 1982;
Woude et al., 1986;
Woude,
Veeger, Hendrich, Rozendal,
&^
Ingen Schenau, 1988).
A^
low mechanical effi-
ciency means a high loss of energy: under steady-state submaximal conditionsa mechanical efficiency of 10
%^ implies that 90
%^ of the liberated aerobic energy
dissipates into heat. Only 10% is used to overcome rolling resistance, air drag,and internal friction in the wheelchair. This is unfavorable when one considersthe 25-year-old design of the chrome-plated foldable wheelchair and the generalcharacteristicsof the population of wheelchair users: a relatively high age, a seden-tary
lifestyle, and a physical disability (Roebroeck, Woude,
&^
Rozendal, 1989).
Moreover, wheelchair users have to rely on the generally untrained and smallmuscle volume of the arms.
Physical activity can be expected to
be
beneficial to the cardiorespiratory
system. Wheelchair use under daily sedentary conditions may be insufficient tostimulate the cardiorespiratory system (Hjeltnes
&^
Vokac, 1979). Lack of suffi-
cient physical activity may lead to obesity and the accelerated development ofcardiorespiratory
ailments. Wheelchair users are at an increased risk
in^
this respect
(Dearwater et al., 1986; Haas, Axen,
Pineda, 1986; Shephard, 1988). The
conventional wheelchair itself is more likely to prohibit than
112
van
der Woude, Veeger, and Rozendal
Vehicle Mechanics In^
a recent Dutch users survey it appeared that the majority of the manually propelled wheelchairs in the study were in deplorable mechanical condition andwere not being maintained (Roebroeck et al., 1989). The effects for the user areineffective ambulation, discomfort, and probably a decreasing radius of action.With respect to ambulation, a number of mechanical aspects are important. Massand mass distribution over the wheels and wheel radius are important for rollingdrag and the effect of gravity when going up an incline.
In^
hand rim wheelchairs
most of the weight should
be over the large rear wheels since they have a low
rolling resistance. Thus rolling drag and the lateral instability on a side slopedecreases (Brubaker, McLaurin,
&^
McClay, 1986; Weege, 1985). Rolling fric-
tion of tires is dependent on the deformation
of the floor surface (material, hard-
ness, smoothness) as well as the tire material (smoothness,
pressure) (Kauzlarich
&^
Thacker, 1985). Several researchers have shown the detrimental effects of weight, tire pressure, and different floor surfaces on rolling drag and energy cost(Brauer, Voegtle,
&^
Hertig, 1981; Engel
&^
Heme, 1981; Glaser
&^ Collins, 1981;
O'Reagan et al., 1981; Wolfe, Waters,
Hislop, 1977).
According to O'Reagan et al. (1981) and Veeger, Woude, Bieleman, and Paul (1988), camber of the rear wheels has little influence
on rolling drag. Cam-
ber improves lateral stability and, according to Clarke (1986) and Hilbers andWhite (1987), it may even improve the reach of the hands to the rim. Misalign-ment of the wheels must be prevented, since any degree of toeing-in or out ofthe wheels increases rolling drag dramatically (O'Reagan et al., 1981). Energyloss due to ball-bearing friction will in general be small but may require main-tenance. Another factor of internal friction may
be associated with frame defor-
mation in foldable wheelchairs. One should consider wheelchairs as ordinaryvehicles. Regular maintenance is important since all frictional losses have to beovercome before efficient ambulation and acceleration is feasible.
Little is known about air resistance in wheelchair ambulation. It is often considered nonrelevant, which is true for indoor use. However, in outdoor useair resistance due to wind and propelling speed can be considerable, especiallyin racing events (Brubaker
&^
McLaurin, 1982). Whether skinsuits are beneficial
in racing events should be studied.
Experimental Methods
Studying wheelchair propulsion
in^
real wheelchairs is a complex problem. Differ-
ent methods are used: a wheelchair
track (Hilbers
&^ White,
1987; Peizer, Wright,
&^ Freiberger, 1964), a stationary platform with instrumented rollers and bear-ings upon which the wheelchair is mounted (Coutts
&^
Stogryn, 1987; Stoboy,
Rich,
&^
Lee, 1971), a stationary device connecting the wheelchair to an existing cycle ergometer (Brattgard et
al.,
1970; Forchheimer
&^
Lundberg, 1986; Wicks,
Lymburner, Dinsdale,
&^
Jones, 1978), or a motor driven treadmill (Bennedik,
Engel,
&^
Hildebrandt, 1978; Engel
&^
Heme, 1984; Gass
&^
Camp, 1979, 1984;
Lakomy, Campbell,
Williams, 1987; Lesser, 1986; Sanderson
&^
Somrner,
1985; Voigt
Bahn,
All
methods have advantages and disadvantages
(Dreissinger
&^
Londeree, 1982).
In^
our experiments
two different experimental
setups are used, a motor driven tre
rpose ergometer.
Ergonomics of Wheelchair Design
113
Motor Driven Treadmill To analyze complete wheelchair concepts, a motor driven treadmill is used. Ona^ motor driven treadmill, mean external power output
(P,
) is measured in a drag
test (Bennedik et al., 1978) in which wheelchair/subject combination is towedover the turning belt with a cable, which is connected
both to the wheelchairluser
combination and a force transducer mounted upon the frame of the treadmill(Figure 1).
During the drag test the subject is passively seated in the wheelchair, and the power output
(Po)
equals the sum of rolling resistance, internal friction in
the wheelchair, and gravitational force when going up an incline. The productof the sum of the drag forces
(FJ
and the mean belt speed
(V)
is the drag power,
which will
be
equivalent to the mean power output during an exercise test on
the treadmill at identical speed and slope. From Po
and cycle frequency
(f),
the
amount of work per cycle
(A)
is calculated. At a submaximal
performance level
the gross mechanical efficiency can
be derived from energy expenditure
(EJ
and
the external power output (Po) (Woude et al., 1986; Woude, Veeger,
&^
Rozen-
dal, 1988b). Wheelchair Ergometer^ To address physiological and biomechanical issues, specific wheelchair ergometerswere designed. These consist of a seat and propulsion mechanism connected toa variable resistance and inertia (Brubaker
&^
McLaurin, 1982; Burkett et al.,
Figure
A^
drag
test on a motor driven
treadmill
used
to^ determine
the mean ex-
ternal power output at different slope levels of a wheelchairluser combination(P,=F,-V). Such tests can also be applied to determine differences
in^ rolling fric-
tion due to mechanical differences.
Ergonomics of Wheelchair Design
115
User-Related
Factors
In the following, results of experiments concerning propulsion technique andaspects of the wheelchairluser
interface will be discussed in more detail. Experi-
ments were predominantly conducted
on the treadmill.
In
the majority of experi-
ments, subjects
conducted a 12-min continuous wheelchair exercise
test in which
either the slope or the speed of the treadmill/ergometer
increased every
3 minutes.
Prior to the experiment, subjects conducted a trial
run
and a warm-up session
was obligatory. In the 3rd minute of each workload step, physiological and bio-mechanical
measures (film, electromyography, torque) were taken. Both wheel-
chair athletes as well as non-wheelchair users were subjected
to the experiments.
Thus oxygen cost, ventilation, heart rate, respiratory exchange ratio, and grossmechanical efficiency were determined. From film data the timing parameters,push range, and amount of worklcycle were determined. Subsequently the angu-lar excursions of the arm segments and trunk were determined. Muscle activitywas determined qualitatively with surface electromyography. Results of statisti-cal analysis (ANOVA, student
t^ tests, post hoc analysis) are presented in terms
of significance (P<0.05). Work Capacity and Training The body of knowledge has increased in the last
years regarding the cardio-
respiratory effects of
arm
work during wheelchair ambulation or
arm
cranking.
These studies are mainly about sport related or rehabilitation training programs(Bar-Or, Inbar,
&^
Spira, 1976; Engel
&^
Hildebrandt, 1977;
Huang, McEachran,
Kuhlemeier, DeVivo,
&^
Fine, 1983; Loftin, Boileau,
&^
Massey, 1988; Nilsson,
Staff,
&^
Pruett, 1975; Sedlock, Knowlton,
&^
Fitzgerald, 1988; Zwiren
&^
Bar-
Or, 1975), methodology of exercise testing (Bar-Or
&^
Zwiren, 1975; Davies
Sargeant, 1974; Gass
Camp, 1984; Glaser
&^
Collins, 1981; Kofsky, Davis,
Shephard, Jackson,
&^
Keene, 1983;
Pitetti, Schnell,
&^
Stray-Gundersen, 1987).
Woude, Veeger, Hendrich, et al. (1988) showed that energy cost and gross mechanical efficiency are not merely dependent on power output alone but alsoon velocity and resisting forcelslope. Equal levels of power output, but at differ-ent velocities and subsequently resisting force, led to a lower mechanical effi-ciency for the high velocity condition.
Both active athletes and sedentary wheelchair users (Taylor, McDonell,
Brassard, 1986; Zwiren
&^
Bar-Or, 1975) or non-wheelchair users have been
studied (Flandrois
et^ al.,
Loftin
et^ al.,
1988; Tahamount, Knowlton, Sawka,
&^ Miles, 1986; Zwiren
Bar-Or, 1975). Marked differences in oxygen cost,
heart rate, and mechanical efficiency can be expected between wheelchair usersand able-bodied persons. Although different in absolute terms, similar trends inthe results with respect to the effects of wheelchair configuration or other experi-mental conditions were found (Woude et al., 1986; Woude, Veeger,
Rozen-
dal, 1988a). A homogeneous group of non-wheelchair users can
be selected
more
easily on physical characteristics, age, and level of training. The effect of theintact body is unclear, and future studies will have to deal with these aspects.
A limited number of studies focused on female athletes
or sedentary wheel-
chair users (Loftin et al., 1988; Sedlock et
al.,
1988; Tahamount et al., 1986).
A^ vast majority of studies, however, focused on subjects with spinal cord lesionsand the effect of the lesions on work capacity (Coutts, 1984; Coutts, Rhodes,
116
van der Woude, Veeger, and Rozendal
&^ McKenzie, 1983, 1985; Coutts
Stogryn, 1987; Dearwater et
al.,
Flandrois et
al.,
1986; Gass
&^
Camp, 1979, 1984; Haas et al., 1986). Differ-
ences in work capacity-related
to disability, age, or physical condition-have
been established (Gass
&^
Camp, 1984; Shephard, 1988). The work capacity of
wheelchair athletes has been evaluated most frequently (Coutts
&^
Stogryn, 1987;
Gass
&^
Camp, 1979; Lakomy et al., 1987; Miles et al., 1982), whereas some attention has been directed to evaluation of actual sport activities (Asayama et^ al.,
1985; Coutts
&^
Schutz, 1988; Ridgway, Pope,
&^
Wilkerson, 1988).
A^ num-
ber of review studies have been published (Davis, Shephard,
&^
Jackson, 1981;
Franklin, 1985; Glaser, 1985; Hoffman, 1986; Sawka, 1986; Shephard, 1988).
The relevance of this research effort is that beneficial effects of physical activity and training for wheelchair users in relation to the rehabilitation processand sports participation, as well as the effects on prevention of cardiovasculardiseases, have been established (Dearwater et
al.,
1986; Franklin, 1985; Glaser,
1985; Haas et al., 1986; Hoffman, 1986; Shephard, 1988).
This major research effort has resulted in a data base on the work physio- logical
effects of wheelchair propulsion. However, a really thorough
understanding
of arm work, as in leg work, does not yet exist. The physiology of wheelchairambulation
lacks a certain normative foundation. Biomechanical research of wheel-
chair ambulation is even more scarce and relations between biomechanical andphysiological aspects have been studied only to a limited extent. Propulsion
Technique
Oxygen cost is an adequate
parameter for evaluating the effectiveness
of steady-
state locomotion with a given wheelchair configuration.
However, metabolic pa-
rameters themselves do not clarify
how
energy is transferred from the user to
the wheelchair or
why
a given wheelchair
configuration
requires less energy than
another.
An
integrated analysis of propulsion technique parameters such as tim-
ing, movement pattern, muscle activation, and force generation is required.
To date, these areas of interest have been studied to a limited extent and separately (Brubaker
McLaurin, 1982; Cerquiglini et al.,
;^ Gaines,
Zornlefer,
Zhao, 1985; Higgs, 1986; Lamontagne, in press; Lees,
in^
press;
Lesser, 1986;
Ridgway et
at.,
Sanderson
&^ Sommer, 1985;
Veeger, Woude,
&^ Rozendal, 1988; submitted; Veeger, Woude, Bieleman,
&^
Paul, 1988; Walsh,
Marchiori,
Steadward, 1986; Woude, Veeger,
Rozendal, 1987; Woude et
al., 1988; Woude et
al.,
1988a).
Propulsion technique covers different phenomena and can be divided into different sets of parameters:
Simple
timing parameters, such as number of pushes the user exerts (cycle frequency
[fJ
and cycle time [CT]), duration of hand-to-rim contact (push
time
[PT]),
recovery phase
(CT
=RT), push range or angle through
which the hand travels on the hand
rim
(PA), and amount of work per cycle;
Study of movement pattern of the arm and trunk segments implies film orvideo analysis of the motions of the upper and lower
arm
and trunk, rela-
tive to each other, during wheelchair propulsion; this results in inforrna-tion about angular displacement, velocity, and
118
van der Woude, Veeger,
and
Rozendal
This general timing pattern holds for speeds
between 0.55 and 4.17 mas' (Woude
et al., 1987; Woude, Veeger, Hendrich, et al., 1988), for wheelchair athletespropelling a racing wheelchair with different hand
rim
sizes or a basketball wheel-
chair (Veeger et al., submitted; Woude, Veeger, Rozendal, et
al.,
for wheel-
chair athletes as well as non-wheelchair users (Woude et al., 1988a; in press),for different
sitting heights (Woude, Veeger, Meys,
&^
Oers, in press), for wheel-
chair propulsion on the treadmill at slopes between 0 and 3", as well as for thestationary wheelchair ergometer at power output levels up to 60
W
(Woude,
Veeger, Hendrich, et al., 1988; Woude et al., in press). An expected increasein peak torque with increasing
velocity was confirmed recently on the ergometer
(Woude et
al.,
in press).
On the other hand, an increase in the resisting force (slope of the tread- mill), but constant velocity leads to increases in worMcycle and cycle frequencyand subsequently to significant decreases in recovery time, whereas push rangeand the push duration remain constant (Veeger et al., submitted; Woude, Veeger,Hendrich, et al., 1988). Lesser (1986) showed that an increase in peak torqueresulted with increasing resistance.
The results of Veeger et al. (submitted) revealed that with increasing mean velocity the movement pattern of the arm segments and trunk changed duringthe push phase (N=5 wheelchair athletes; basketball wheelchair; 0.55-1.39 m-6';2 and 3" slope). Maximum and minimum values of the trunk angle shifted for-ward whereas the maximum upper arm ante- and retroflexion angles decreasedwith increasing velocity (P<0.05). The elbow angle showed no significant
changes,
but the peak angular velocity of the elbow as well as upper arm and trunk showedsignificant increases (P<0.05).
Optimum
Cycle
Frequency.
Optimum technique in terms of energy cost
may improve sport performance, prevent injuries of longstanding excessiveactivity, and enhance proper wheelchair use under daily-use conditions. How-ever, little is known about the adequacy of the movement pattern and timing inwheelchair ambulation in general. The frequency of movement at a given poweroutput influences energy cost.
An
optimum frequency of motion is apparent in
different cyclic movement patterns (cycling, walking) but has not been establishedfor wheelchair ambulation.
To evaluate hand rim wheelchair ambulation with regards to the effect of different imposed cycle frequencies on cardiorespiratory responses and propul-sion technique, six experienced wheelchair athletes and six non-wheelchair users,respectively, conducted four and three wheelchair exercise tests on a treadmillat different
velocities (0.55- 1.39 m-
s-' and a constant slope). In each test a 3-min
period at a freely chosen cycle frequency (FCF= 100%)
was followed by four
3-min blocks of paced cycle frequencies at 60,80, 120, and 140%
FCF. Simple
propulsion technique parameters were studied with high-speed film.
Analysis of variance revealed a significant effect (P<0.05) of cycle fre- quency on oxygen cost
and
mechanical efficiency for the group of wheelchair
athletes (WS), indicating
an optimum close to the freely chosen cycle frequency
at any given velocity (Slope 2") (Sargeant
&^
Woude, 1988). The optimum and
freely chosen frequency increased with velocity as is indicated above, the latterfrom 0.67 to 1.03 cycles/sec over the range studied (P<0.05).
Oxygen cost was
+_^10
%^ less at 100
%^ FCF compared to
or 140%
FCF
Mechanical efficiency at 100%
FCF was 8.5,9.7, 10.4, and 10.
%^ at the four
Ergonomics of Wheelchair Design
WS-GROUP
/N=6)
1W^
C(C
EFREQUENCY
Figure
Gross mechanical efficiency
(N=
wheelchair athletes)
in^
dependence
of four imposed cycle frequencies
80, 120, 140%)and the freely chosen cycle
frequency (100%)
at four different velocities and a 2" slope of the treadmill.
velocities, respectively (Figure
The optimum cycle frequency in terms of
energy cost and mechanical efficiency was similar for a group of six non-wheelchair users propelling the same wheelchair at the three highest velocitiesand at a slope of 1
"^.^ The fact that untrained non-wheelchair users selected a fre-
quency of motion close to a physiologic optimum implies that the selection ofan^
optimum frequency is not merely a consequence
of practice but at least partly
reflects a physiologically determined optimum, possibly dependent for exampleon velocity of contraction and power output of the muscles used. The timing pa-
Ergonomics of Wheelchair Design
I^
I^
i
0
1
2
wf
(degrees)
Figure
Mean oxygen cost of
(N=
non-wheelchair
users propelling
four differ-
ent wheelchairs on the treadmill
at^ different slopes and
a^ mean velocity of
m.s-'.
chairs and their physiological benefits for use in sports and recreation. Theexplanation of the other results is more complicated. One would expect the rac-ing wheelchair to be superior to the daily-use wheelchair, but not to be at sucha great disadvantage compared with the tricycles. Although inexperience mayhave influenced the subjects' achievement in the racing wheelchair, other factorsmay be present. Next to hemodynamic differences between hand rim propulsionand lever and crank modes, biomechanical differences
in^
terms of force genera-
tion (leverage, grip, pushlpull forces, reaction forces, and
trunk
stability) and
muscle activity (which muscles, timing of agonists and antagonists, trajectory)seem relevant but have not been studied in this context.
Gangelhoff et al. (1988) recently studied lever and crank work modes. Lever ergometry appeared superior to crank ergometry and led to lower cardiorespiratoryresponses. Again the explanation
is complicated
and speculative
due to the different
forms of motion. Important variables in this respect may be the seat position,the mechanical advantage and leverage of the system, and the form and positionof the hand grip. With respect to the lever, relevant factors may be whether both
122
van der Woude, Veeger, and Rozendal
push and pull forces can be exerted, whether the trunk is involved, and whetherthe hands move alternately or synchronously. According to Glaser, Sawka,Laubach, and Suryaprasad (1980) and Engel et al. (1976), alternate movementsof the arms are more efficient. This contrasts with findings
of Lesser (1986) con-
cerning asynchronous lever propulsion. Bobbert (1988), however, found that ina vertical one-legged jump more than 50% of the maximum height of the bodycenter of gravity present in two-legged jumps can be attained.^ Hand
Rim
Characteristics
Higgs (1983), who was the first to analyze the relation between sports wheel-chair design and athletic achievements during the Paralympics, showed greaterachievement for those athletes in lightweight wheelchairs with smaller rims, in-creased camber, and more inclined and rearward placed seats. Although the greaterachievement may have been due to a lower rolling resistance and internal fric-tion, or to the athlete's better work capacity, the design and fitting of the wheel-chairs might have played a decisive role. Engel and Henze (1981) and Bmbakerand McLaurin (1982) presented the first experimental
evidence for lower cardio-
respiratory responses during wheelchair propulsion in a sports wheelchair com-pared with a conventional hand
rim
wheelchair under similar conditions. Parziale
et al. (1986) recently presented similar (preliminary) data. Hilbers and White(1987) conducted a similar analysis but presented more results and an appropri-ate description of the wheelchairs under study. Propelling a sports wheelchair(9.8 kg) at a given speed led to a 17% lower energy cost in comparison witha conventional hand rim wheelchair (18.9 kg). Woude et
al.
(1986) found the
tested racing wheelchair to be superior to a daily-use active wheelchair in termsof oxygen cost, heart rate, and drag forces, but not in terms of mechanical effi-ciency. The latter may
be
due to the differences in external power output (i.e.,
drag forces). Vehicle mechanics (weight distribution) will have a decisive role,but perhaps also important are proper fitting of the wheelchair to the user andrelated ergonomic advantages.
Characteristics of hand rims have been evaluated to a limited extent. Leh- mann, Warren, Halar, Stonebridge, and DeLateur (1974), Brubaker and McLaurin(1982), and Lesser (1986) have evaluated commercially
available rims and some
prototypes with different biomechanical and physiological methods (force mea-sures, electromyography, endurance time). Gaines and La (1986) conducted auser survey among 28 spinal cord injured subjects. It is clear that contour charac-teristics such as pegs, coating, profile, and tube diameter are dependent on boththe nature and extent of the disability and grip strength. Relations to anthropo-metric dimensions are obvious but have not yet been studied.
There are two major differences
between
racing wheelchairs and lightweight
or conventional hand
rim
wheelchairs: the small hand rim size
(f
30 cm diameter)
in racing wheelchairs and the low and inclined seat position. Both characteristicswere related to success in Higgs' (1983) study. Woude, Veeger, Rozendal, etal.^
(1988) studied the effect of different hand rim sizes on energy expenditure and propulsion technique with a group of
(n^
=8) wheelchair athletes. Subjects
propelled their own similar type racing wheelchair (Speedy Wheely) with fivedifferent hand rim diameters (Dl-D5: 0.30-0.56 m) in five separate tests on themotor driven treadmill. The tests were all conducted under equal external loads(0.5"; V=0.83-4.
m-s-').
van der Woude, Veeger, and Rozendal
SEAT
HEIGHT N=^
NW
%
V=.56rnls
6 4
I^
I^ -
I^
1
140
WOW
ANGLE
Figure
Mean
values of
gross
mechanical
efficiency
of^ (N=9)
non-wheelchair
users
propelling
a^ basketball
wheelchair
at different
sitting heights (elbow angles: 100,120,
and
four
velocities.
a shorter push time and over a shorter range, which requires a change in the torquecharacteristics
of the hands. These factors may explain the enhanced energy cost
with increasing sitting
height. Data must
be^
gathered on more subjects
and smaller
increments in seat height before a predictive model for seat height is feasible.However, the data here suggest a means of ergonomic optimization within thehand rim wheelchair design. Camber In^ view of the opinion that an increased camber angle of the rear wheels enhanceslateral stability as well as the reach of the rim and allows a less hampered armmotion, a positive effect on energy expenditure and propulsion technique maybe expected (Clarke, 1986; Higgs, 1983; Hilbers
&^
White, 1987). An experi-
ment was conducted on the effects of different camber angles on physiological
Ergonomics o
f Wheelchair Design
125
and propulsion technique parameters, movement patterns, and muscle activity(Veeger, Woude, Bieleman,
&^
Paul, 1988). The rationale behind this experiment
was that an increased camber angle is believed to improve the reach of the handsto the rims, and to improve the alignment of the shoulder, elbow, and hand inthe plane of the hand
rim,
thus decreasing inefficient abduction.
Eight non-wheelchair users conducted four wheelchair exercise tests at camber angles of
and 9" on the treadmill. Results of this experiment
were revealing: analysis of variance showed no effect of camber angle on thephysioIogical parameters.
A^
small effect was found in some parameters of propul-
sion technique. Preliminary electromyographicresults showed an absence of ac-tivity in the m. deltoideus pars acromialis (abductor of the arm) during the pushphase. The main activity of this muscle occurs during the second half of the recov-ery and not, apart from a brief burst, at the end of the push phase. There is nosubstantial difference in activity between
0 and 9" camber. Both
mm.
pectoralis
major and deltoideus pars clavicularis have their major activity during the pushphase and appeared highly active. This may explain the abduction during the pushphase as being a much more passive side effect of a complex process of anteflex-ion. The following hypothesis needs further clarification: anteflexion instigatedby^
mm.
pectoralis major and deltoideus pars clavicularis leads to endorotation and abduction in the shoulder joint, as a side effect, since the elbow and handare part of a closed chain between shoulder and hand rim.
In this project no kinematic or physiological advantages of camber were found. Since wheelchairs with cambered wheels have better static stability, cam-bered rear wheels are preferable. Given that a basketball wheelchair was studiedwith a group of non-wheelchair users, further study seems warranted. In racingwheelchairs with a low and inclined seat and small hand rims, as analyzed byHiggs (1983), camber may be of greater relevance
than
comfort alone. More-
over, the top-to-top distance between the rims may be of relevance in terms ofoptimization of wheelchairs in general.
Conclusions
One may conclude there is increasing research interest in wheelchair locomotionand design. With the help of experimental research, design features may beexplained and confirming evidence substantiated. Thus ergonomic guidelines maybe established for optimally fitting the wheelchair to the user in general as wellas under sports conditions. As of yet, however, there is still a need for consider-able research effort from a combined physiological, anatomical, and biomechanicalperspective to shed light on the underlying processes in wheelchair ambulation.This effort should be directed to different categories of wheelchair users (age,disability, athletes, sedentary) and different wheelchair designs.
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