FOR PEOPLE WITH DISABILITIES, manual wheelchair

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1 1865 Impact of a Pushrim-Activated Power-Assisted Wheelchair on the Metabolic Demands, Stroke Frequency, and Range of Motion Among Subjects With Tetraplegia S. David Algood, MS, Rory A. Cooper, PhD, Shirley G. Fitzgerald, PhD, Rosemarie Cooper, MPT, ATP, Michael L. Boninger, MD ABSTRACT. Algood SD, Cooper RA, Fitzgerald SG, Cooper R, Boninger ML. Impact of a pushrim-activated powerassisted wheelchair on the metabolic demands, stroke frequency, and range of motion among subjects with tetraplegia. Arch Phys Med Rehabil 2004;85: Objectives: To determine differences in metabolic demands, stroke frequency, and upper-extremity joint range of motion (ROM) during pushrim-activated power-assisted wheelchair (PAPAW) propulsion and traditional manual wheelchair propulsion among subjects with tetraplegia. Design: Repeated measures. Setting: A biomechanics laboratory within a Veterans Affairs medical center. Participants: Fifteen full-time manual wheelchair users who had sustained cervical-level spinal cord injuries. Interventions: Participants propelled both their own manual wheelchairs and a PAPAW through 3 different resistances (slight, 10W; moderate, 12W; high, 14W) on a wheelchair dynamometer. Each propulsion trial was 3 minutes long. Main Outcome Measures: Primary variables that were compared between the 2 wheelchairs were participants mean steady-state oxygen consumption, ventilation, heart rate, mean stroke frequency, and maximum upper-extremity joint ROM. Results: When using the PAPAW, participants showed a significant (P.05) decrease in mean oxygen consumption and ventilation throughout all trials. Mean heart rate was significantly lower when using the PAPAW for the high resistance trial. Stroke frequency was significantly lower when using the PAPAW for the slight and moderate resistances. Overall joint ROM was significantly lower when using the PAPAW. Conclusions: For subjects with tetraplegia, PAPAWs reduce the energy demands, stroke frequency, and overall joint ROM when compared with traditional manual wheelchair propulsion. Key Words: Kinematics; Metabolism; Rehabilitation; Tetraplegia; Wheelchairs. From the Departments of Rehabilitation Science & Technology (Algood, RA Cooper, Fitzgerald, R Cooper, Boninger); Physical Medicine & Rehabilitation (RA Cooper, Fitzgerald, R Cooper, Boninger); and Bioengineering (RA Cooper, Boninger), University of Pittsburgh; and Human Engineering Research Laboratories, VA Rehabilitation Research and Development Center, VA Pittsburgh Healthcare Systems (Algood, Fitzgerald, R Cooper, Boninger), Pittsburgh, PA. Presented in part to the RESNA 26th International Conference, June 21, 2003, Atlanta, GA. Supported in part by the National Institute on Disability and Rehabilitation Research (grant no. H133N000019), US Department of Education, Rehabilitation Services Administration (grant no. H129E990004), and the US Department of Veterans Affairs, Rehabilitation Research and Development Service (grant no. F2181C). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Rory A. Cooper, PhD, Human Engineering Research Laboratories (151-R1), VA Pittsburgh Healthcare System, 7180 Highland Dr, Pittsburgh, PA 15206, rcooper@pitt.edu /04/ $30.00/0 doi: /j.apmr by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation FOR PEOPLE WITH DISABILITIES, manual wheelchair propulsion is commonly an inefficient means of mobility. 1 Furthermore, people with cervical-level spinal cord injuries (SCIs), that is, tetraplegia, may find manual wheelchair propulsion even more difficult because of upper-extremity muscle weakness. If combined with upper-extremity pain, a person with tetraplegia could quickly lose the ability to propel independently a manual wheelchair, which could lead to the loss of independent mobility and decreased activity. It is well documented 2-7 that upper-extremity pain and injuries are prevalent among manual wheelchair users (MWUs). The upper extremities were not developed for manual wheelchair propulsion, and these people often experience shoulder, elbow, and wrist pain and injuries. In fact, the incidence of shoulder pain has been reported to be as high as 73% among MWUs. 6 In a survey study of 77 people with paraplegia, Gellman et al 8 noted that 49% showed signs and symptoms of carpal tunnel syndrome (CTS) and further noted that the prevalence of CTS increased with length of time after injury. MWUs with tetraplegia are often less efficient during propulsion than MWUs with paraplegia. This may be caused in part by decreased physical capacity and impaired upper extremities in MWUs with tetraplegia. Beekman et al 9 concluded that, in general, MWUs with tetraplegia travel less distance and with a higher oxygen consumption rate than those with paraplegia. The kinematic characteristics of manual wheelchair propulsion have been investigated extensively Many researchers 8,19 agree that propelling with a high cadence and excessive range of motion (ROM) of the joints can lead to upper-extremity pain and cumulative trauma disorders. Koontz et al, 20 when testing 27 subjects with paraplegia, observed higher peak joint forces in positions in which the shoulder was at maximum flexion in the sagittal plane and minimal abduction. When comparing the effects of the level of SCI on shoulder joint kinematics, Kulig et al 21 suggested that MWUs with tetraplegia have an increased likelihood of compressing subacromial structures because of high push force combined with weakness of thoracohumeral depressors. Thus, people with tetraplegia may be even more susceptible to pain and injuries of the shoulder joint, and avoiding positions where the shoulder is excessively flexed becomes even more important. Alternative methods of wheelchair propulsion, such as leverdrive units, arm cranks, and geared hubs, have been developed. For the most part, these have fallen short in presenting feasible and commercially appealing solutions. 22,23 Pushrim-activated power-assist wheelchairs (PAPAWs) offer an alternative between manual wheelchairs, lever-drive systems, and powered mobility devices. PAPAWs are typically manual wheelchairs with a permanent magnet, direct-current motor in each rear

2 1866 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood Fig 1. The PAPAW used in this study. hub, where the user s manual pushrim input is supplemented proportionally by the motor (fig 1). Studies have shown PA- PAW users to have a significant improvement of the mechanical efficiency, joint ROM, and metabolic demands However, participants included in previous studies have been limited to either MWUs with thoracic-level SCIs (paraplegia), multiple sclerosis, or no disability. No study conducted to date focused on MWUs with tetraplegia, a population who could significantly benefit from PAPAWs. The purpose of this study was to compare PAPAW propulsion and traditional manual wheelchair propulsion characteristics among MWUs with tetraplegia. It was hypothesized that there would be significant differences among several primary outcome variables including energy expended, stroke frequency, and upper-extremity joint ROM between users of the 2 wheelchairs. own manual wheelchair and a PAPAW on a computer-controlled wheelchair dynamometer. 29 The experimental setup was similar to that described by Shimada et al. 16 Participants were asked to maintain a speed of 0.9m/s through 3 different dynamometer resistance conditions (slight, moderate, high) for both the PAPAW and their own manual wheelchair. The order in which the wheelchairs were presented to each participant was randomized. Once the participant was in each wheelchair, the order of resistances was randomized. The resistance conditions simulated trials of propelling on a flat tiled floor (slight: 0.9m/s, 10W), a flat carpet (moderate: 0.9m/s, 12W), and uphill (high: 0.9m/s, 14W). 29 Each of the 6 propulsion trials was 3 minutes in length. After testing, steady state of the participant was confirmed by an investigator who visually observed that metabolic and heart rate values had reached a plateau after 2.5 minutes. Participants were provided with 5 minutes to get acclimated to the test setup and were provided with a 5-minute rest between each trial. They were also provided with a visual display of their real-time speed throughout the propulsion trials. The PAPAW available for this study was a Yamaha JWII a mounted to a Quickie 2 b folding-frame manual wheelchair, which was selected and adjusted to best match partcipants own wheelchairs current seat dimensions (seat width, seat depth, backrest height, seat to footplate length, pushrim diameter, rear wheel diameter, axle position). Metabolic Data Collection Four minutes of physiologic data were collected for each trial: 1 minute resting and 3 minutes of propulsion. Each subject s steady-state rate of oxygen consumption (V O2 in ml kg 1 min 1,V O2 in ml/min) and ventilation rate (V 2 in L/min) were acquired by using an Aerograph VO2000 metabolic cart, c which was calibrated before each testing session. This system collects inhaled and expired gases from the participant via a mouthpiece and tube at a sampling rate of 150Hz. Each participant s nose was pinched with a nose clamp to METHODS Subject Recruitment Participants were recruited through the Human Engineering Research Laboratories registry. They were initially contacted by either letter or telephone. To determine the number of subjects for the study, data (means, standard deviations [SDs]) were used that had been collected on subjects with paraplegia by using a similar protocol. 25 Power analyses were computed and revealed that, for all variables, 15 subjects were needed to provide at least 75% power in the study. To meet the inclusion criteria, participants had to be between the ages of 18 and 65, full-time MWUs for at least 1 year with tetraplegia, free from pressure ulcers and shoulder pain, and have no history of cardiopulmonary disease. This study received prior approval by the appropriate human studies institutional review boards. Each participant was provided with information about the safety and intent of the tests, and signed informed consent was obtained before any testing. Experimental Protocol Participants were asked to abstain from eating for 2 hours before testing. For all testing, participants propelled both their Fig 2. Location of light-emitting diode markers used during the kinematic testing. Legend: 1, temporomandibular joint; 2 acromion process; 3, olecranon; 4, lateral epicondyle; 5, radial styloid; 6, ulnar styloid; 7, third MPJ; 8, fifth MPJ; 9, markers for the trunk.

3 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood 1867 Table 1: Subject and Personal Wheelchair Demographics Subject No. Age (y) Injury Level Years Postinjury Chair Frame Type* (seat width seat depth) C Folding (18 18) C Rigid (16 16) C Folding (18 16) C7 2.1 Folding (17 17) C Rigid (16 19) C5 7.9 Rigid (18 19) C7 7.8 Rigid (15 15) C Rigid (18 18) C Rigid (16 16) C Rigid (14 15) C Folding (16 18) C6 0.9 Rigid (20 20) C Rigid (16 16) C Folding (18 18) C7 7.1 Rigid (17 17) *All participant wheelchairs were ultralight weight manual wheelchairs (Medicare code K0005). Measurements are in inches. prevent air loss from the system. Heart rate data were digitally collected by using a Polar T31 d wireless heart rate monitor and heart rate was continuously monitored throughout testing, as well as monitored for 15 minutes on completion of the testing. The Polar T31 system records a person s heart rate every 5 seconds, and averages it over 30-second intervals. Kinematic Data Collection Two Optotrak 3D 3020 e motion analysis cameras were used to collect the position data of infrared markers placed on both sides of the participant s body. The location of the markers included the temporomandibular joint, acromion process, olecranon, lateral epicondyle, radial styloid, ulnar styloid, third metacarpophalangeal joint (MPJ), fifth MPJ, and 3 markers for the trunk. Figure 2 provides a visual depiction of the marker placement on a participant s body. When transferring between the 2 wheelchairs, the markers were undisturbed. Markers were also placed on both sides of the wheelchair s rear axle. Kinematic data were collected at a 60-Hz frequency and filtered with an eighth-order, zero-phase digital Butterworth filter. For each wheelchair setup (PAPAW, own), a set position was recorded with the Optotrak camera. For the set position, participants held their arms in full adduction, with the elbows flexed to 90, forearms at 0 in pronation and supination, and wrists at 0 of ulnar and radial deviation. The set position was taken to ensure similar wheelchair setup between the participants own manual wheelchairs and the PAPAWs. Data Reduction Computational methods and calculations were carried out by using Matlab. f For the physiologic, heart rate, and kinematic data, the last 30 seconds of each trial were analyzed for statistical purposes. For stroke frequency and ROM, the first 10 successive strokes were averaged for the variables during each trial. Overall joint ROM angles (eg, flexion extension) were calculated by using the methods described in Boninger 18,30,31 and colleagues. This method involves defining a local coordinate system at the shoulder, elbow, and wrist and then describing the movements of each joint based off these systems. For example, the arm and trunk markers are used to define the axes of a local coordinate system based at the shoulder. The model used assumes that the only motion occurring in the trunk is flexion and extension. The calculated movements included wrist flexion and extension; ulnar and radial deviation; forearm supination and pronation; elbow flexion and extension; shoulder flexion and extension, abduction, and adduction; internal and external rotation; and horizontal flexion and extension. Statistical Analysis Descriptive statistics were performed for all variables, and histograms were evaluated for normal distributions. Paired sample t tests (P.05) were used to compare the means of data that were normally distributed (ie, ventilation rate; stroke frequency; shoulder, elbow, and wrist ROM), and Wilcoxon ranksum tests were performed on data that were not normally distributed (ie, V O2 in ml/min, V O2 in ml kg 1 min 1, velocity, heart rate). In addition, a mixed-model analysis of variance (ANOVA) was used to determine whether differences existed between the 2 types of chairs and the 3 resistance conditions. A mixed model was used because it allows for comparison between the 2 wheelchairs even though the same participant performed the testing of the wheelchairs. Statistical analysis was performed by using both SPSS g and SAS h softwares. Table 2: Metabolic Energy Consumption and Mean Heart Rate V O2 (ml/min) Ventilation (L/min) V O2 (ml kg 1 min 1 ) Heart Rate (bpm) Trial (n 15) Personal PAPAW Personal PAPAW Personal PAPAW Personal PAPAW 0.9m/s, 10W * m/s, 12W m/s, 14W NOTE. Values are mean SD. One subject was unable to complete a high-resistance trial using his own manual wheelchair due to fatigue. *P.002; P.001; P.004; P.001; not significant.

4 1868 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood Table 3: Subjects Mean Stroke Frequency Trial Personal Wheelchair PAPAW P 0.9m/s, 10W (n 13) m/s, 12W (n 13) m/s, 14W (n 12) NOTE. Values are mean strokes per second SD. RESULTS Participants Fifteen full-time MUWs with tetraplegia (cervical-level SCI) participated in the testing. The demographics included 12 men and 3 women; age range, 27 to 52 years (mean SD, y); height range, 152 to 193cm (mean, cm); and weight range, 45 to 116kg (mean, kg). All participants used ultra lightweight wheelchairs as their primary means of mobility. Table 1 further describes the personal manual wheelchairs of the participants, in addition to the level of their injury, the number of years postinjury, and their age. Variations of Mean Velocity The overall mean velocities throughout the slight (10W) and moderate (12W) resistances did not differ significantly (P.29, P.17, respectively) between the 2 wheelchair configurations (personal vs PAPAW), and the mean velocities for these conditions were.92.12m/s for both chairs. However, during the highest (14W) resistance trial, subjects showed a significantly lower mean velocity (P.009) when using their own manual wheelchair than when propelling with the PAPAW (.79.13m/s,.99.10m/s, respectively). Metabolic Energy Consumption The physiologic variables compared between the 2 wheelchair configurations were oxygen consumption (V O2 in ml kg 1 min 1,V O2 in ml/min), ventilation (V E in L/min), and heart rate (in beats per minute). Table 2 shows the means of the 4 variables, the SDs, and the results of the paired t tests. Because of fatigue, 1 subject was unable to complete a high resistance trial when using a manual wheelchair. For oxygen consumption and ventilation, a significant difference was noted between the 2 wheelchairs. Mean heart rate was significantly reduced when participants used the PAPAW during the high resistance trial. However, mean heart rate for the slight and moderate resistances did not differ significantly between the 2 wheelchairs. Results of the mixed-model ANOVA showed that the PAPAW was responsible for the observed changes in all dependent variables. Stroke Frequency and ROM From the kinematic data that were collected, 13 of the 15 participants data could be used. The 2 kinematic data sets that could not be used were because of excessive marker dropout during the testing, which did not permit proper filtering or analysis with Matlab. The demographics of those that were used were 10 men and 3 women; age range, 28 to 52 years (mean, y); height range, 152 to 193cm (mean, cm); and weight range, 45 to 116kg (mean, kg). Table 3 shows the mean stroke frequency for the 2 wheelchairs throughout all resistance conditions. Although stroke frequency was significantly reduced for participants for the slight (P.001) and moderate (P.001) resistances, there was no significant difference between the 2 chairs when resistance was at the highest setting (P.078). Tables 4 through 6 show the overall ROM angles for the shoulder (table 4), wrist joints (table 5), and elbow (table 6) for participants when propelling their own manual wheelchair and a PAPAW. During propulsion at the slight resistance, paired sample t tests showed significantly lower ROM when using the PAPAW for shoulder flexion and extension (P.003), internal and external rotation (P.032), horizontal flexion and extension (P.028) (table 4), and wrist ulnar and radial deviation (P.028) (table 5). At the moderate resistance, a significant decrease in ROM was observed for shoulder flexion and extension (P.005), internal and external rotation (P.002), horizontal flexion and extension (P.043) (table 4), as well as forearm supination and pronation (P.008) and ulnar and radial deviation (P.014) (table 5). At the highest resistance, there were significant decreases in overall ROM when using the PAPAW for all joint movements except for shoulder abduction and adduction. The set position that was taken for each trial showed no significant difference (P.42) between the location of the hub marker and the participants acromion process. DISCUSSION The need to maintain functional, independent mobility is extremely important among MWUs. It is common for a person with tetraplegia, particularly one who is several years postin- Table 4: Results of Shoulder ROM Testing With the PAPAW and Subjects Own Wheelchairs Flexion and Extension Internal and External Rotation Abduction and Adduction Horizontal Flexion and Extension Trial Personal PAPAW P Personal PAPAW P Personal PAPAW P Personal PAPAW P 0.9m/s, 10W (n 13) NS m/s, 12W (n 13) NS m/s, 14W (n 12) NS NOTE. Values are mean degrees SD. Abbreviation: NS, not significant.

5 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood 1869 Trial Table 5: Results of Wrist ROM Testing With the PAPAW and Subjects Own Wheelchairs Flexion and Extension Forearm Supination and Pronation Ulnar and Radial Deviation Personal PAPAW P Personal PAPAW P Personal PAPAW P 0.9m/s, 10W (n 13) NS NS m/s, 12W (n 13) NS m/s, 14W (n 12) NOTE. Values are mean degrees SD. Table 6: Results of Elbow ROM Testing With the PAPAW and Subjects Own Wheelchairs Trial Flexion and Extension Personal PAPAW P 0.9m/s, 10W (n 13) NS 0.9m/s, 12W (n 13) NS 0.9m/s, 14W (n 12) NOTE. Values are mean degrees SD. jury, to move from a manual wheelchair to a powered mobility device. Reasons for this transition include weight gain, upperextremity injuries and pain from overuse, and overall decreased physical capacity. However, there are numerous factors to consider when deciding on a mobility device, and switching from one device to another could have a significant impact on a person s lifestyle. For example, an MWU who is considering making the transition to an electric-powered wheelchair may not have a home environment or an accessible vehicle that would accommodate such a device. Here again, a PAPAW would offer an alternative solution to a powered mobility device. Maintaining a certain level of activity with manual wheelchair propulsion could also benefit the person s overall physical capacity. Reduced physical capacity in MWUs with tetraplegia occurs for several reasons, including reduced function in the upper extremities, impaired sympathetic cardiac regulation, and decreased venous return. 32 As this study revealed, when using a PAPAW, participants showed decreased physical exertion while maintaining, or even improving, their propulsion velocity. For people with decreased physical capacity, conserving energy during routine tasks, such as propelling uphill or across a carpeted hallway, might allow a person to maintain function while performing other necessary activities, such as transferring to a different surface. The prevention of upper-extremity pain and repetitive strain injuries in MWUs is extremely important because both can severely limit a person s ability to maintain functional, independent mobility. Limiting excessive joint ROM and high stroke frequency could potentially decrease the likelihood for developing pain and injuries. In our study, the ROM and stroke frequency of subjects stayed the same throughout the trials when using the PAPAW. Even at the high dynamometer resistance, little change in the stroke frequency or ROM was observed. This reflects the proportional nature of the assistance that the PAPAW provides. As the difficulty of the trials increased, the amount of assistance provided by the PAPAW increased and the subject s effort remained the same. Stroke frequency did not differ significantly between the 2 chairs when resistance was at the highest setting. Furthermore, the stroke frequency for the participants lowered during the most difficult trial when using their own wheelchair. This seems counterintuitive because one would expect the user to increase the cadence as the physical demands of the task increased. A possible cause of this is that some participants were fatiguing at the high resistance and not maintaining the target 0.9m/s when pushing their own manual wheelchair. Therefore, they were propelling less often than in previous trials. This was confirmed because there was a significant difference in velocity observed between the 2 wheelchairs at the highest resistance (P.009). As mentioned earlier, avoiding propulsion positions where the shoulder joint is excessively flexed in the sagittal plane and decreasing the amount it is abducted is desirable. When looking at the overall ROM angles, there was a significant difference for shoulder flexion and extension but not for abduction and adduction. When the ROM was broken down into individual movements, there was no significant reduction in shoulder abduction when using a PAPAW. However, there was a significant difference in mean shoulder flexion for all conditions. Gellman et al 8 suggested that the high prevalence of CTS was caused by the combination of repetitive trauma to the extended wrist while propelling, combined with the forced extension of the wrist when performing pressure relief. Therefore, avoiding positions where the wrist is in extreme extension could further prevent the development of CTS. As revealed in our results, there was only a significant change between the 2 wheelchairs in overall wrist flexion and extension during the high resistance. However, when the wrist movement was broken down between flexion and extension, there was a significantly lower extension angle for the PAPAW during the slight (P.006), moderate (P.002), and high (P.005) resistance conditions. Thus, the PAPAW showed a decrease in wrist extension during propulsion. Examination of the position of the acromion process in relation to the wheelchair hub of both wheelchairs, combined with the fact that no differences were found in shoulder abduction and adduction ROM between wheelchairs, shows that the subject s position in each chair, and the height and width of each chair, were comparable. Given this information, and by using the mixed-model ANOVA, we concluded that the PA- PAW was the likely cause for change in the dependent variables. The relatively short propulsion trials during the first phase might not allow all participants to reach steady state. However, several participants were fatiguing when using their own manual wheelchairs and after only propelling for 3 minutes. We

6 1870 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood also observed that the metabolic data had plateaued for the majority of participants who were tested. Combined with the knowledge that we were working with a population with decreased physical capacity, we believed that 3 minutes was a sufficient propulsion trial length. Other limitations to the study include small sample size, high variability of the metabolic data, and marker dropout during the kinematic testing. Based on the limitations of this study, further testing of PAPAWs would be beneficial. Metabolic efficiency, upperextremity joint ROM, and stroke frequency are not the sole factors contributing to pain and repetitive strain injuries. Other factors, such as the forces applied by the wheelchair user at the pushrim, should be considered as well. Future biomechanics studies with this device and subject population should investigate the forces and moments that occur at the joints when propelling. A likely, future test will involve testing the device s effectiveness during simulated activities of daily living. In such a test, one would be able to note the limitations of PAPAWs, such as the added width and weight of the wheels. It is probable that people with tetraplegia would have difficulty taking a PAPAW apart and transferring it into their car. More than likely, the most appropriate test to determine a PAPAW s effectiveness with this subject population would be to allow MWUs to take the device home with them and use it in their home environment and community. CONCLUSIONS The findings of this study have expanded the knowledge of how PAPAWs can positively influence the propulsion capabilities of people with tetraplegia. PAPAWs have the potential to reduce metabolic energy expenditure while decreasing upperextremity ROM required by MWUs with tetraplegia when propelling a wheelchair. However, these are not the only factors that should be considered when addressing one s overall seating and mobility needs. PAPAWs should be considered for people with tetraplegia who are capable of using them safely and effectively throughout all daily activities. References 1. Beekman CE, Miller-Porter L, Schoneberger M. Energy cost of propulsion in standard and ultralight wheelchairs in people with spinal cord injuries. Phys Ther 1999;79: Bayley JC, Cochran TP, Sledge CB. The weight-bearing shoulder. The impingement syndrome in paraplegics. J Bone Joint Surg Am 1987;69: Nichols PJ, Norman PA, Ennis JR. Wheelchair user s shoulder? Shoulder pain in patients with spinal cord lesions. Scand J Rehabil Med 1979;11: Gellman H, Sie I, Waters RL. Late complications of the weightbearing upper extremity in the paraplegic patient. Clin Orthop 1988;Aug(233): Sie IH, Waters RL, Adkins RH, Gellman H. Upper extremity pain in the postrehabilitation spinal cord injured patient. 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7 WHEELCHAIR DEMANDS IN TETRAPLEGIA, Algood Shimada SD, Cooper RA, Boninger ML, Koontz AM, Corfman TA. Comparison of three different models to represent the wrist during wheelchair propulsion. IEEE Trans Neural Syst Rehabil Eng 2001;9: Dallmeijer AJ, Hopman MT, van As HH, van der Woude LH. Physical capacity and physical strain in persons with tetraplegia; the role of sport activity. Spinal Cord 1996;34: Suppliers a. Yamaha Motor Co, 2500 Shingai, Iwata, Shizuoka, , Japan. b. Sunrise Medical Corp, Quickie Div, 2842 Business Pk Ave, Fresno, CA c. MedGraphics, 350 Oak Grove Pkwy, St. Paul, MN d. Polar CIC Inc, 370 Crossways Park Dr, Woodbury, NY e. Northern Digital Inc, 103 Randall Dr, Waterloo, ON N2V 1C5, Canada. f. The MathWorks Inc, 3 Apple Hill Dr, Natick, MA g. SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL h. SAS Institute Inc, 100 SAS Campus Dr, Cary, NC