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Overuse injury (repetitive strain injury) of upper extremity
is remarkably common in individuals who use manual wheelchair as
daily living. Previous studies have related the long-term
wheelchair propulsion with the upper extremity injuries. Most
published studies simplified the movement of upper extremity via
two-dimensional description and their results have indicated the
need of three-dimensional analysis. Seat of wheelchair is an
important interface in providing the force needed for propelling
the wheelchair. Different seat position will change the
interface of users and the wheelchair. The purpose of this study
is to investigate the effect of seat position changes on the
kinematics and kinetics of upper extremity with full three-
dimensional description. A 3 by 3 matrix of seat positions was
used. We hypothesize that the differences in kinematics and
kinetics of upper extremity appeared at different seat position.
Thirteen ambulatory men were instructed to propel the wheelchair
on the level ground. A standard type manual wheelchair with an
instrumented wheel consists of a six-component load cell was
used to collect the forces and moments applied on the handrim by
users directly. Several reflective markers were placed on the
subject used to define the segments of upper extremity for
calculating joint kinematics and kinetics of upper extremity via
the inverse dynamics method. ExpertVisionTM system was used to
collect the trajectory data of the markers while the subject was
propelling the wheelchair on the level ground. The isolated
joint moment data collected in this study were expressed in
terms of a wheelchair propulsion strength rating (WPSR). The
WPSR is defined as the ratio between joint moment generated
during propulsion and that generated during a maximum isometric
strength test at each direction, as an index indicating the
percentage of loading. The maximum isolated isometric moments of
each subject were evaluated by the Kin-ComTM AP dynamometer.
Multivariate ANOVA was used to analyze all parameters in
relation to the seat height and seat axle horizontal position.
Comparisons were made for the individual effect of seat height
and seat axle horizontal position, also the interaction of these
two factors. The effect of seat position changes appeared
significantly for joint range of motion and WPSR, but no
significant difference found in temporal parameters and
propulsion efficiency. The movement pattern of wheelchair
propulsion can be described more detail by the three-dimensional
data-acquisition system, both in kinematics and kinetics. This
study supports the hypothesis that the kinematics and kinetics
of wheelchair propulsion would be affected by seat position
changes. High WPSR in the shoulder and wrist joints match the
high incidence of shoulder and wrist over-use injury.
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