Stroke pattern refers to the trajectory of the hand during the recovery phase of manual wheelchair propulsion. During the propulsive or push phase, the hand follows the path of the handrim. However, during the recovery phase the user can choose any trajectory to prepare for the next push. Four stroke patterns have been identified for users of manual wheelchairs based on the pattern used during the recovery phase (Shimada et al. 1998; Boninger et al. 2002; Koontz et al. 2009):
- Semicircular (SC): the hands fall below the hand rim during recovery phase.
- Single looping over propulsion (SLOP): the hands rise above the hand rim during recovery phase.
- Double looping over propulsion (DLOP): the hands rise above the hand rim, then cross over and drop below the hand rim during the recovery phase.
- Arcing (ARC): The third metacarpophalangeal (MP) follows an arc along the path of the hand rim during the recovery phase.
The following articles examine the stroke patterns as well as the kinetics and kinematics of the different stroke patterns in relation to the potential for upper extremity injury due to suboptimal biomechanics and/or chronic overuse.
There have been five studies that have investigated the effectiveness of stroke patterns in wheelchair propulsion in the spinal cord injured population.
Boninger et al. (2002) studied the stroke patterns of 38 individuals with paraplegia while propelling their own wheelchair on a dynamometer at two different steady state speeds. The SC and DLOP patterns were found to have significantly lower cadence and least time spent in each phase of propulsion. The SC and ARC patterns had the greatest amount of time spent in propulsion relative to the recovery phase. A correlation has been found between cadence and the risk of median nerve injury (Boninger et al. 1999). The authors concluded a stroke pattern that minimized cadence may reduce the risk of median nerve injury.
Richter et al. (2007a) studied the stroke patterns of 25 individuals with paraplegia propelling their own wheelchairs at self-selected speeds on a treadmill set to level, 3° and 6° grades. In this study, the SC pattern was not used by any of the subjects. For level propulsion, the number of subjects using the remaining three patterns was fairly evenly distributed. However, once the subjects started going uphill 73% of participants used the ARC pattern. No significant difference was found in the handrim biomechanics between the different stroke patterns. The authors caution against training wheelchair users to adopt a certain pattern until more is known about the consequences.
Kwarciak et al. (2012) investigated the effects of the four different stroke patterns on hand rim biomechanics and upper extremity electromyography (EMG) in people experienced with w/c use. They found variability in the participants’ chosen normal propulsion stroke patterns, with 60% using a double loop pattern, 24% using the single loop pattern, and 8% each for using the ARC pattern and the semi-circular pattern. Despite the few significant values in the study, the authors felt the findings supported the recommendations for upper limb preservation that less frequent, long smooth strokes are required. The DL and SC patterns generated the best combination of biomechanics producing the longest contact angle, lowest cadence values, and smallest braking moments. While there were no significant values, the DL also has the advantage of 35% lower elbow muscle activity. However, the authors recommend that users individual style and comfort drive decision between the two (i.e., imposing changes from one pattern to the other is not needed) The authors did question the viability of the single loop pattern, as it produced the largest contact impact at the hand rim, the largest amount of muscle activation and the second worst values for cadence, peak force contact angle and braking moment. The arching pattern results in this study produced suboptimal handrim biomechanics but the low muscle demand is the most metabolically efficiency, to which the authors suggest may be useful for uphill propulsion.
Raina et al. 2012b identified the purpose of their study as threefold; 1) to determine whether the stroke propulsion pattern affects the magnitude of hand/forearm velocity prior to hand rim contact, 2) to determine if the hand movements of one of the four typical stroke patterns results in a higher effectiveness of propulsion and 3) if differences in propulsion patterns exist between participants with paraplegia versus tetraplegia. No differences were noted between patterns but significant differences were found between the participant groups of paraplegia and tetraplegia. The differences were primarily in the wrist velocity prior to contact with the participants with paraplegia being more highly correlated to magnitude of force impact compared to the participants with tetraplegia, but both correlations being significant. The similar findings were found for effectiveness of impact forces, with the participants with paraplegia having significantly greater impact force effectiveness than participants with tetraplegia. Also noted was a difference in muscle activity particularly for the participants with tetraplegia having a higher radial force impact. The authors noted that the difference in radial force impact may be related to reduced force effectiveness in this group (i.e., weaker grip strength affecting sustained contact with handrim). Therefore, in this study, authors proposed that radial force may have been used by participants with tetraplegia to increase friction on the hand rim during the push phase. Given that in this study all participants with tetraplegia demonstrated low impact force effectiveness in all stroke patterns for propulsion, improving the effectiveness of the impact force or reducing the magnitude of impact force would require alternate means of increasing friction at the hand pushrim interface (e.g., friction gloves) or alterative mechanisms for propulsion (e.g., power assist wheels). These differences in the initial push phase of propulsion between paraplegic and tetraplegia injury levels hold important considerations for maintenance of upper extremity health.
Koontz et al. (2009) explored propulsion patterns, and kinetic and kinematic variables at start up propulsion over a linoleum floor, a carpeted floor and a 5° incline ramp with 29 people with spinal cord injury who used manual wheelchairs. They defined start up as the first three push strokes from a stopped position as most people reached average velocity of propulsion on similar surfaces based on other larger study results. The authors reported that some patterns were difficult to discern and some were hybrids of two propulsion patterns, therefore using three raters to gain consensus was recommended due to this variability. They found that on any surface, the most common first stroke pattern was an Arc, however those who switched after the first stroke to an under-rim pattern reached higher velocities and experienced less negative forces during start up than those who stayed with an Arc pattern. The only except to this was the ramp, where many participants continued to use the Arc propulsion pattern. The authors speculate this is related to the tendency of the wheelchair to roll backwards on the ramp during the recovery phase; the Arc pattern has a shorted recovery phase. The impact of the first three stroke patterns on function and upper extremity maintenance is seemingly minimal until the consideration of the frequency of start/stop occurrences throughout the day is considered. The authors suggest greater attention needs to be paid to the propulsion to propulsion training particularly the patterns used.
Feng et al (2010) examined the kinematic differences between two stroke propulsion patterns (pumping and circular) with a focus on the glenohumeral joint excursion as related to shoulder impingement. Based on the research literature they defined impingement as “…contact between the anterior aspect of the humerus and the acromial arch which creates compressive forces on the glenohumeral joint” (p 448), with a range of internal or external rotation beyond 30° of forward flexion or 30° of abduction. The study wheelchair was adjusted for each participant for optimal propulsion positioning (i.e., 30° elbow flexion when hand on top of rim, distance between rear corner of seat and axis equaled 15% of participant’s arm length). The authors concluded that the pumping stroke pattern of propulsion travelled more and stayed longer in the impingement range than the circular stroke pattern. The authors indicated that further study is required to determine if this range of glenohumeral joint excursion is related to shoulder impingement injuries, and if the use of the pumping stroke style contributes to shoulder impingement injuries. There are, however, a few limitations of this study, which make it difficult to generalize the findings to clinical practice. The first is the small study size (n=10). The second is the use of a pre-determined set up for the study wheelchair as opposed to examining the participant in their own w/c set up. The third is the use of only two stroke patterns, it is not clear why the authors identified only two stroke patterns and did not related them to patterns identified in the literature despite referencing articles where the four stroke patterns are identified. The fourth is the limited description of the amount of internal and external rotation that is considered as part of the definition of shoulder impingement.
There is level 4 (from four case series studies; Boninger et al. 2002; Richter et al. 2007; Raina et al. 2012b; Kwarciak et al. 2012) evidence that the typical propulsion stroke patterns used by individuals with spinal cord injury varies across the four stroke patterns regardless of level of injury.
There is level 4 (from one case series study; Boninger et al. 2002) evidence that the semicircular and double-loop-over propulsion wheelchair stroke patterns reduce cadence and time spent in each phase of propulsion, thus using these patterns may reduce the risk of median nerve injury.
There is level 4 (from two case series studies; Richter et al. 2007; Raina et al. 2012b) evidence that there is no difference in hand rim biomechanics during propulsion between the four stroke patterns. However, there is also level 4 (from two case series studies; Boninger et al. 2002; Kwarciak et al. 2012) evidence that the semicircular and double-loop-over propulsion stroke patterns offer the best combination of biomechanics for propulsion.
There is level 4 (from one case series study by Raina et al. 2012b) evidence propulsion biomechanics differ between people with paraplegia and tetraplegia with the latter group producing lower wrist velocity prior to contact, less magnitude of force impact, and higher radial force.
There is level 4 (from one case series study; Feng et al. 2010) evidence that the movements associated with particular patterns may increase the risk of shoulder impingement, with pumping stroke pattern exposing the shoulder to greater risk than the circular pattern.
There is level 4 (from two case series studies; Kwarciak et al. 2012; Boninger et al. 2002) evidence that the ARC stroke pattern has suboptimal biomechanics, but the lowest muscle demand, therefore holds potential for making it useful for short duration, high force propulsions such during ascending a hill or ramp.
There is level 4 evidence (from two case series studies; Koontz et al. 2009; Richter et al. 2007a) to suggest that the Arc pattern is the most frequently used propulsion pattern used when ascending a slope greater than 3⁰.
There is level 4 evidence (from one case series study; Koontz et al. 2009) to suggest that it takes the first three propulsion strokes from a resting positioning to reach steady state velocity and while the Arc pattern is most frequently used for the first stroke, those who change to an under-rim pattern for the subsequent strokes, reach steady state velocities quicker and experience less negative mechanical forces during start up propulsion.
The evidence suggests that stroke pattern use varies based on individual preference and the environmental demands with some stroke patterns being more effective to achieve specific outcomes.
The evidence supports that to avoid accumulating shoulder impingement stresses proper technique must be considered based on a combination of kinematics (e.g., contact angle, stroke frequency, movement patterns at each joint), stroke pattern, wheelchair fit and set up.