ABSTRACT

The purpose of this study was to compare the stroke frequency and joint excursion of manual wheelchair users (MWUs) when pushing their own manual wheelchairs and pushrim activated power assist wheelchairs (PAPAW). Repetitive strain injuries (RSIs) resulting from wheelchair propulsion are often linked to both the number of strokes an individual takes, and excessive range of motion of involved joints during the propulsion cycle. Fifteen subjects with tetraplegia were asked to propel their own manual wheelchair and a PAPAW on a wheelchair dynamometer (roller system) at varying resistances. When using the PAPAW, individuals showed a significant decrease (p < .05) in both frequency and upper extremity excursion across all but a few trials. These results indicate that when using a PAPAW, an individual pushes less often and with less range of motion than with their own wheelchair, thereby decreasing the likelihood for developing RSIs and upper extremity pain.

BACKGROUND

For persons with disabilities who have upper extremity weakness, the traditional manual wheelchair is an effective, but at times an inefficient, means of mobility (1). According to the latest Census statistics, there are over 2.2 million wheelchair users in the United States alone, and this number is increasing. An important issue for wheelchair users is injuries related to propelling the wheelchair. The upper extremity serves as the main means of propulsion for the wheelchair user, and has been described as "walking with the arms." (2) The upper extremity was not designed for this sort of function and these individuals often experience shoulder, elbow and wrist pain. In fact, the incidence of shoulder pain has been reported to be as high as 51% among MWUs. (3) Other studies have noted wrist and elbow pain to be reported in 25% to 80% of the wheelchair user population. (4)

For many years, mobility devices have been limited to powered wheelchairs, manual wheelchairs, or powered scooters. Pushrim Activated Power Assist Wheelchairs (PAPAWs) offer an alternative between manual wheelchairs and powered wheelchairs. The PAPAW unit automatically supplements the user's manual pushrim input with additional rear-wheel torque for up to 4 miles per hours traveling velocity. The amount of added torque is provided proportional to the user input to the pushrims and movement and braking assistance is provided in both forward and backward directions. PAPAWs tested during this study are Quickie 2 manual wheelchairs fitted with the JWII power assist wheels, developed by the Yamaha Motor Corporation.

RESEARCH QUESTION

Do significant differences exist in the stroke frequency and excursion for persons with tetraplegia while propelling a PAPAW and their own manual wheelchair through different levels of resistances on a wheelchair dynamometer?

METHOD

Fifteen manual wheelchair users (MUWs) with tetraplegia (cervical level spinal cord injury) participated in the study. The demographics included: 12 males and 3 females, age 27 to 52 years (mean 37.3, SD 7.3), height 60 to 76 inches (mean 70.9, SD 4.5), and weight 100 to 256 lbs (mean 173.1, SD 42.7). Each subject was provided with information about the safety and intent of the tests, and signed consent forms were obtained prior to any testing. For data collection, subjects propelled both their own manual wheelchair and a PAPAW in random order on a computer-controlled wheelchair dynamometer. They were asked to maintain a speed of two miles per hour through three different resistance conditions (slight, moderate, and high) for both the PAPAW and their own manual wheelchair. The resistance conditions simulated trials of propelling on a flat tiled floor (slight), a flat carpet (moderate) and uphill (high). Each of the six trials was three minutes in length with data collected for the final 30 seconds of the last minute. Subjects were provided with five minutes rest between each trial. The JWII selected for each subject was mounted to a Quickie 2 that best matched their own wheelchair's current seat dimensions.

An OPTOTRAK 3D 3020 motion analysis system (Northern Digital, Inc.) was used to collect the position data of infrared markers (IRED) placed on the wheelchair user's body. The location of the makers included the subject's: temporomandibular joint, acromion process, lateral epicondyle, radial styloid, third metacarpophalangeal (MP) joint, fifth MP joint, ulnar styloid, olecranon and three markers for the trunk. When transferring between the two wheelchairs, the markers were undisturbed. For data analysis, the markers used to determine the excursion and stroke frequency included the right side acromion process, lateral epicondyle, and third metacarpophalangeal joint. Paired sample t-tests (p < .05) were used to compare the means of the excursion and stroke frequency.

RESULTS

Tables 1-3 show the means for each trial, and the significant differences as the results of the paired sample t-tests. Table 4 compares the stroke frequency of the user's own manual wheelchair in comparison to the PAPAW. The excursions and stroke frequencies not significantly decreased when using the PAPAW are indicated in bold. One subject was unable to complete a trial using his or her own manual wheelchair due to fatigue.

DISCUSSION

The prevention of upper extremity pain and repetitive strain injuries in MWUs is extremely important. Excessive range of motion of the joints and high stroke frequency have been well documented in literature as two of the leading causes of pain and RSIs. For individuals with higher-level spinal cord injuries, such as tetraplegia, propulsion may already be difficult because of upper extremity muscle weakness. Added to this upper extremity pain, and one could quickly loose the ability to independently propel a manual wheelchair, leading to loss of mobility and decreased activity.

The results of this study reveal that using a PAPAW could significantly reduce the stroke frequency and excursion of involved joints during wheelchair propulsion. Of note, excursion and stroke frequency of individuals stayed the same throughout the trials when using the PAPAW. Even at higher dynamometer resistances, little change in the stroke frequency or excursion was observed. This reflects the proportional nature of the assistance that the PAPAW provides. As the difficulty of the trials increases, the amount of assistance provided by the PAPAW increases, and the individual effort remains the same. Stroke frequency was not significantly different between the two chairs when resistance was at the highest setting. This was likely due to the fact that the subjects were fatiguing at the high resistance and not maintaining the target two miles per hour when pushing their own manual wheelchair. Therefore, they were propelling less often than in previous trials. However, the propulsion speed data needs to be analyzed to confirm this.

Previous studies have revealed that PAPAWs can reduce metabolic energy expenditure, improve function during daily activities, and improve mobility and participation among individuals with paraplegia. (5) Future studies involving people with tetraplegia include an activities of daily living evaluation, and home trials, where the subjects will take a PAPAW with them for four weeks, and record time spent in the wheelchair, distances traveled, and a complete of a consumer satisfaction survey.

ACKNOWLEDGMENTS

We would like to acknowledge Yamaha Motor Corporations, USA for providing the JWII hubs used in this study. Additional funding was provided by the National Institute for Disability and Rehabilitation Research, SCI Model Systems Program (H133N000019).