Performance of Manual Propulsion in Wheelchair Bound Patients Using a New Seating Design
ABSTRACT
When propelling a manual wheelchair, the power for propulsion is generated mainly from upper extremities. Change of posture in a wheelchair can alter the body's stability and efficiency in functional tasks, including propelling a wheelchair. A new seating design, which shifts pressure from the ischial tuberosities towards the thighs, was tested. The purpose of this study was to evaluate the performance of wheelchair occupants during propulsion using the new seating design, by evaluating force generation and muscle activities. The kinetic and muscle activities were recorded while the subjects were performing manual propulsion tasks in the new seating design. It was found that there was no significant change in the manual propulsion of the user during the tasks. The performance related to manual wheelchair propulsion was found to be similar to that of a regular wheelchair design for this new seating mechanism.
KEY WORDS:
Pressure, Seating, Shoulder, Posture
INTRODUCTION
Manual wheelchair propulsion, which requires the production of large quantities of power, is considered to have a relatively low gross mechanical efficiency (1). The injuries to upper extremities in manual wheelchair users can be attributed to the combination of high demand for power output with the given limited muscle mass in the shoulder area and the specific anatomy of the shoulder area (2,3). Sitting posture in the wheelchair may affect the performance of manual propulsion and may have influence on the likelihood of injuries to soft tissue of upper extremities of wheelchair users (4,5).
A seating design, which alternates the pressure on and position of the ischial tuberosities and lumbar areas, has been introduced to the wheelchair by our group, in the attempt to promote sitting tolerance in wheelchair users. In preliminary studies on healthy subjects, we found that sitting with the lowered BPS (back part of the seat) and lumbar support in place, defined as WO-BPS posture, induced a significantly reduced interface pressure on the subject's ischium, an increased total and segmental lumbar lordosis, a forwardly rotated sacrum, and larger lumbar intervertebral heights (6).
However, the effect on the wheelchair users' performance, when using this seating mechanism, has not been tested. This study was designed to address this concern. The following factors were taken into consideration during the evaluation of wheelchair propulsion: activation of key muscles, and the force generated by the upper extremities.
It is hypothesized that using the WO-BPS sitting posture will not undermine the performance of wheelchair manual propulsion. The purpose of this study was, therefore, to compare the performance of wheelchair occupants during propulsion using the WO-BPS sitting posture , to that of the Normal posture, by evaluating force generation and muscle activities.
METHODS
Measurements:
The EMG electrodes were placed on the following muscles: the long head of Triceps (Tri), the Biceps (Bic), the Deltoid Medialis (Delt), upper part of the Trapezius (Tarp), upper part of the Infraspinatus (Inf), lateral portion of the Serratus Anterior (Serr Ant), Latissimus Dorsi (Lat), and Pectoralis major (Pec). A common reference electrode was placed at the spinous process of C7.
Signal from the electrodes was recorded with Delsys EMG system (Delsys Inc, USA). Maximum voluntary contraction (MVC) for each muscle was recorded before performing the propulsion tasks, for later normalization of the EMG. This was accomplished by performing the lifting efforts and exercises using a Theraband. A 50-seconds rest period was used between the MVC trials to avoid muscle fatigue. In addition, the Gothenburg shoulder model (7) was used to simulate the behavior at the shoulder joint for each activity, producing an anticipated set of activated muscles and an expected level of activation.
The wheelchair used for the experiment was a modified Küschall © Ultra-Light wheelchair (Invacare AG, Allschwil, Switzerland), and the backrest was a J2 ® Plus Back backrest (Sunrise Medical Corp., Longmont, CO) . The native seat of the wheelchair was replaced with our seat design, and an air bladder was embedded under the backrest cushion, to allow the configuration of WO-BPS posture. The wheelchair was instrumented with a 6-axis force transducers (JR3, Woodland, CA, USA) to determine the torque applied to the modified push-rim of the wheelchair during manual propulsion. As seen in Fig. 1, the push-rim was attached to the force sensor (normally attached to the wheel) and the sensor measures forces and moments exerted on the wheel (F x , F y , F z , M x , M y and M z ). Data from the 6-axis force sensor were low-pass filtered and the following force components were calculated: the normal force to the wheel (F N ), tangential force (F T ), and the total force (F tot ) applied on the hand-rim.
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Manual propulsion tasks: static Pushing forward, static Braking , Uphill and Downhill propelling, and static Push-up . The subject was asked to perform these tasks twice while the seating mechanism was configured as Normal or WO-BPS postures. For each task, results from the same subject were averaged before performing averaging across all subjects. Comparison was done between data from Normal and WO-BPS postures. A paired t -test was used to detect significant differences and the significance level was set at 0.05.
RESULTS
The forces and moment (kinetic) applied to the hand rim of the wheelchair are shown in table 1.
Sitting Posture |
F N (N) |
F T (N) |
F tot (N) |
M Z (N.m) |
|---|---|---|---|---|
WO-BPS Pushing Braking Uphill Downhill |
14.0±6.1 61.5±34.7 12.5±50.5 37.6±9.1 |
19.0±4.2 36.0±20.1 16.1±116.3 15.5±10.8 |
76.2±7.5 98.4±24.3 111.0±78.1 50.2± 6.5 |
-7.3±0.8 17.5±3.2 -8.7±9.7 10.0±1.7 |
Normal Pushing P Braking P Uphill P Downhill P Push-up |
14.0±0.1 0.312 69.3±30.1 0.877 15.9±13.8 0.318 40.7±9.3 0.708 80.5±30.2 |
14.8±9.7 0.046 48.1±16.4 0.654 48.7±37.7 0.330 11.8±7.9 0.662 15.4±11.9 |
69.2±7.7 0.536 109.9±20.3 0.727 64.8±37.7 0.328 51.4±13.9 0.901 89.8±29.4 |
-5.8±1.0 0.256 17.5±3.4 0.994 -7.1±5.4 0.782 9.9±0.7 0.889 -3.3±2.9 |
Except for the tangential force (F T ) during the task of Pushing forward, forces and moments applied to the pushrim during propulsion tasks were not significantly different between Normal and WO-BPS postures. F T had a P -value of 0.046 which indicates that a significantly larger tangential force was generated when using the WO-BPS posture. The highest and smallest of the F N were for the Push-up (80.5±30.2N) and Uphill (12.5±50.5N) tasks, respectively. The F T was higher during Braking and Uphill tasks. The upper extremities exerted the highest load during Uphill and Braking tasks as it was indicated by the F tot (Table 1).
Table 2 shows the EMG results for eight of the subjects.
EMG |
Tri |
Bic |
Delt |
Inf |
Lat |
Serr Ant |
Trap |
Pec |
|---|---|---|---|---|---|---|---|---|
Pushing |
0.174±0.126 |
0.086±0.017 |
0.136±0.068 |
0.320±0.195 |
0.244±0.050 |
0.400±0.246 |
0.114±0.077 |
0.099±0.089 |
Braking |
0.046±0.023 |
0.287±0.165 |
0.101±0.034 |
0.373±0.227 |
0.152±0.097 |
0.131±0.067 |
0.174±0.051 |
0.163±0.059 |
Uphill |
0.165±0.126 |
0.107±0.168 |
0.117±0.079 |
0.209±0.227 |
0.140±0.081 |
0.066±0.023 |
0.065±0.023 |
0.236±0.108 |
Downhill |
0.072±0.054 |
0.061±0.055 |
0.098±0.054 |
0.066±0.048 |
0.069±0.071 |
0.099±0.085 |
0.079±0.037 |
0.082±0.056 |
Push-up |
0.146±0.010 |
0.049±0.023 |
0.090±0.076 |
0.383±0.221 |
0.319±0.078 |
0.155±0.136 |
0.042±0.030 |
0.392±0.243 |
No significant difference was detected for the EMG data between the Normal and WO-BPS postures (P>0.05). Triceps, as an extensor, showed more activity during the Pushing and Push-up tasks. Biceps was also more activated for the Pushing . The output of the Gothenburg shoulder model is fairly consistent with the measured EMG data, with the expected muscle groups activating, and only moderate deviation between the expected and actual EMG data.
The values for the Push-up trials are also presented on each table. As expected, force data is almost entirely in the normal direction, and there is substantial muscle activity in Tri, Inf, Lat, Serr Ant, and Pec.
DISCUSSION
The overall results in this experiment indicate that the new posture does not compromise the performance of propulsion. There was no significant change between the muscles activated for each task between each posture, and there was no significant difference in the forces and moments generated for each task between each posture. Therefore, from preliminary testing of the new seating design, it does not seem that the WO-BPS posture will undermine propulsion, confirming our hypothesis. It should be noted that these results are derived from healthy participants, and the results of these tests may change for a user of a manual wheelchair for several reasons. Many persons who use a manual chair daily have developed postural habits that might not be healthy for the shoulders, could have previous shoulder problems, and may have stronger upper extremities from the repetitive motion of propulsion. When a person becomes tired from sitting, their posture is also affected. Therefore, testing of individuals confined to wheelchairs is necessary.
REFERENCE
- van der Helm, F.C.T and Veeger, H.E.J. 1996, Quasi-Static Analysis of Muscle Forces in the Shoulder Mechanism During Wheelchair Propulsion, Journal of Biomechanics, 29, 39-52.
- Pentland, W. 1994, Upper Limb Function in Persons With Long-Term Paraplegia and Implications for Independence, Paraplegia, 32,211-224.
- van Drogelen, S., Veeger, H.E.J., Angenot, E., van der Woude, L.H.V., Janssen, T.W. 2002, Mechanical Strain in the Upper Extremities During Wheelchair Related Activities, 4 th Meeting of the International Shoulder Group, (Cleveland, OH), 2002.
- Bolin, I., Bodin, P., Kreuter, M. 2000, Sitting Position- Posture and Performance in C5-C6 Tetraplegia, Spinal Cord, 38(7), 425-34.
- Stankovits, S. 2000, The Impact of Seating and Positioning on the Development of Repetitive Strain Injuries of the Upper Extremity in Wheelchair Athletes, Work, 15(1), 67-76.
- Makhsous, M., et al. Sitting Pressure in a Wheelchair with Adjustable Ischial and Back Supports, RESNA 26th International Conference. 2003. Atlanta, GA
- Makhsous, M. (1999). Improvements, Validation and Adaptation of a Shoulder Model. PhD Thesis, Polymetric Dept . Gothenburg, Sweden, Chalmers University of Technology. ISBN: 91-7197-810-0.
Correspondence Author:
Mohsen Makhsous,
PhD,
Sensory Motor Performance Program,
Rehabilitation Institute of Chicago,
345 E Superior, Suite 1406,
Chicago, IL 60611.
Email: m-makhsous2@northwestern.edu
