A 2-D model of wheelchair propulsion

PURPOSE: To illustrate the potential benefits of kinetic and kinematic models in the exploration of biomechanical studies as illustrated using a simple 2-D static optimization model of wheelchair propulsion. METHOD: A four-bar linkage analysis was used to determine sagittal plane motion through the range of wheelchair propulsion. Using anthropometric measures of wheelchair users, this analysis determined the angles of shoulder and elbow flexion/extension at a given point in the propulsion cycle. Maximal strength inputs for the model were collected from isokinetic measurements of shoulder and elbow moments. The torque inputs were given as functions of sagittal plane joint angles. Through selection of appropriate model performance criteria, optimization techniques determined shoulder and elbow torque contributions throughout the propulsion cycle. Variations in the model parameters of anterior-posterior (AP) seat position and handrim size went used to show potential of model to evaluate wheelchair configuration using the performance criteria of propulsive moment (Mo) and efficiency as defined by fractional effective force (FEF). RESULTS: The model was able to predict the magnitude and direction of force applied to the handrim from shoulder and elbow moments. These joint moments may be examined along with the generated wheelchair axle propulsion moment. While the model showed no significant changes in either Mo or FEF for AP seat changes, an increase in handrim size was shown to increase FEF. CONCLUSIONS: This model was able to simulate wheelchair propulsion and allow for performance analyses. The open nature of the model allowed for tweaking of the kinematic inputs to examine the sensitivity of such factors as seat position and handrim size in wheelchair propulsion. Strength inputs to the model may also be altered to study the potential effects of strength training or muscle weakness.     

Wheelchair propulsion kinematics in beginners and expert users: influence of wheelchair settings

Background

Biomechanical studies have linked the handrim wheelchair propulsion with a prevalence of upper limb musculoskeletal disorders. The purpose of this study was to examine the influence of the wheelchair settings on upper limb kinematics during wheelchair propulsion. Recordings were made under various wheelchair configuration conditions to understand the effect of wheelchair settings on kinematics parameters such shoulder, elbow and wrist angles.

Methods

Ten experts and ten beginners’ subjects propelled an experimental wheelchair on a roller ergometer system at a comfortable speed. Twelve wheelchair configurations were tested. Kinematics were recorded for each configuration. Based on the hand position relatively to the handrim, the main kinematic parameters of wheelchair propulsion were investigated on the whole propulsion cycle and a key event such as handrim contact and release.

Findings

Compared to the beginner subjects, all the experts’ subjects generally present higher joint amplitude and propulsion speeds. Seat height and antero-posterior axle position influence usage of the hand-rim, timing parameters and configurations of upper limb joints. Results seem to confirm that low and backward seat position allow a greater efficiency. Nevertheless, according that proximity of joint limit is a well known factor of musculoskeletal disorders, our results let us think that too low and backward seat position, increasing joints positions and amplitudes, could increase the risk of upper limb injuries in relation with manual wheelchair propulsion.

Interpretation

Kinematic differences highlight that future studies on wheelchair propulsion should only be done with impaired experienced subjects. Furthermore, this study provides indications on how wheelchair settings can be used for upper limb injury prevention.     

Kinematic analysis of handbike propulsion in various gear ratios: implications for joint pain

BACKGROUND: Though considered more efficient and less constraining than the hand-rim wheelchair, the handbike has rarely been studied especially as regards its kinematic parameters. The hypothesis of this investigation is that the range of upper extremity motions are risk factors for joint pain during handbiking as is the case during hand-rim wheelchair propulsion. This paper aims to study handbike propulsion in maximal sprint conditions in order to determine potential risk factors for joint pain. METHODS: Eight able-bodied participants with no experience in handbike propulsion performed three sprints of 8 s each using three gear ratios in a handbike mounted on a home-trainer. The mean velocity per arm cycle, the cycle frequency, the angular parameters for the upper extremities were calculated, as well as the corresponding angular accelerations, with the help of a 3D movement analysis. FINDINGS: An increase in gear ratio (22/21, 32/21, and 44/21) significantly increases the maximal velocity, the flexion/extension of the trunk, as well as the adduction/abduction of the elbow, while it reduces the frequency of movements and the flexion/extension angular accelerations of the shoulder and the elbow. Regardless of what gear ratio is used, maximal angular amplitudes of the upper extremities are comparable to the values obtained with a hand-rim wheelchair. Interpretation. The high amplitudes and fast angular joint accelerations of the upper extremity found in this study are near or superior to the ergonomic recommendations generally advised. These considerations could be taken into account to prevent overuse injuries.     

Comparison of shoulder load during power-assisted and purely hand-rim wheelchair propulsion

Background

Repetitive forces and moments are among the work requirements of hand-rim wheelchair propulsion that are related to shoulder injuries. No previous research has been published about the influence of power-assisted wheelchair propulsion on these work requirements. The purpose of our study was therefore to determine the influence of power-assisted propulsion on shoulder biomechanics and muscle activation patterns. We also explored the theoretical framework for the effectiveness of power-assisted propulsion in preventing shoulder injuries by decreasing the work requirements of hand-rim wheelchair propulsion.

Methods

Nine non-wheelchair users propelled a hand-rim wheelchair on a treadmill at 0.9 m/s. Shoulder biomechanics, and muscle activation patterns, were compared between propulsion with and without power-assist.

Findings

Propulsion frequency did not differ significantly between the two conditions (Wilcoxon Signed Rank test/significance level/effect size:4/.314/−.34). During power-assisted propulsion we found significantly decreased maximum shoulder flexion and internal rotation angles (1/.015/−.81 and0/.008/−.89) and decreased peak force on the rim (0/.008/−.89). This resulted in decreased shoulder flexion, adduction and internal rotation moments (2/.021/−.77; 0/.008/−.89 and1/.011/−.85) and decreased forces at the shoulder in the posterior, superior and lateral directions (2/.021/−.77; 2/.008/−.89 and2/.024/−.75). Muscle activation in the pectoralis major, posterior deltoid and triceps brachii was also decreased (2/.038/−.69; 1/.015/−.81 and 1/.021/−.77).

Interpretation

Power-assist influenced the work requirements of hand-rim wheelchair propulsion by healthy subjects. It was primarily the kinetics at rim and shoulder which were influenced by power-assisted propulsion. Additional research with actual hand-rim wheelchair users is required before extrapolation to routine clinical practice.     

Biomechanical analysis of wheelchair propulsion for various seating positions.

The pattern of propulsion was investigated for five male paraplegics in six seating positions. The positions consisted of a combination of three horizontal rear-wheel positions at two seating heights on a single-purpose-built racing wheelchair. To simulate wheelchair propulsion in the laboratory, the wheelchair was mounted on high rotational inertia rollers. For three trials at each seating position, the subjects propelled the designed wheelchair at 60 percent of their maximal speed, which was determined at the beginning of the test session. At each trial, the propulsion technique of the subject was filmed at 50 Hz with a high-speed camera for one cycle, and the raw electromyographic (EMG) signal of the biceps, brachii, triceps brachii, pectoralis major, deltoid anterior, and deltoid posterior muscles were simultaneously recorded for three consecutive cycles. The digitized film data were used to compute the angular kinematics of the upper body, while the EMG signals were processed to yield the linear envelope (LE EMG) and the integrated EMG (IEMG) of each muscle. The kinematic analysis revealed that the joint motions of the upper limbs were smoother for the Low positions-since they reached extension in a sequence (wrist, shoulder, and elbow), when compared to the High positions. Also, the elbow angular velocity slopes were found to be less abrupt for the Backward-Low position. It was observed that in lowering the seat position, less IEMG was recorded and the degrees of contact were lengthened. Among the seat positions evaluated, the Backward-Low position had the lowest overall IEMG and the Middle-Low position had the lowest pushing frequency. It was found that a change in seat position caused more variation in the IEMG for the triceps brachii, pectoralis major, and deltoid posterior. The trunk angular momentum was not found to be affected by a change in seat position which may be related to the variability among the subject's technique of propulsion or to a posture compensation.     

Muscular endurance and wheelchair propulsion in children with cerebral palsy or myelomeningocele.

Bivariate correlations between muscular endurance or resistance used during six-repetition maximum (6-RM) for eight upper body exercises (shoulder flexion, extension, abduction, internal and external rotation, elbow flexion, extension and shoulder flexion/elbow extension (bench press), 50-meter dash, and 12-minute wheelchair propulsion tests were examined in six children with diagnoses of cerebral palsy or myelomeningocele. Correlations were determined before and after resistance training. Before training, only elbow extension correlated significantly with the 12-minute test. Following training, significant correlations (p less than or equal to 0.05) were found between all 6-RM exercises and 12-minute test scores. Additionally, significant correlations were found between all 6-RM exercises (except elbow flexion, which approached significance) and 50-meter dash scores. The results of this clinical case investigation indicate that the relationship between muscular endurance (6-RM) and wheelchair propulsion improves as muscular endurance increases.     

Influence of training on biomechanics of wheelchair propulsion.

A quasi-experimental longitudinal design was used to compare pre- and posttraining biomechanical and physiological characteristics of wheelchair propulsion in manual wheelchair users (MWCU) across fresh and fatigue states. An instrumented wheelchair ergometer, 3D motion analysis, and computerized open-circuit spirometry were used to collect joint kinetics and kinematics, handrim kinetics, propulsion temporal characteristics, and oxygen uptake pre- and posttraining during a submaximal exercise test to exhaustion. Each subject (n = 19) participated in a specific intervention program of supervised therapeutic exercise (strengthening, stretching, and aerobic exercise) for 6 weeks. Pre- and posttraining measurements were compared with the use of ANOVA with repeated measures. Significant training effects included increased exercise loads for all strengthening activities, decreased stroke frequency, increased maximum elbow extension angle, increased trunk and shoulder flexion/extension range of motion (ROM), increased handrim propulsive moment, increased wrist extension moment, and increased power output. Results suggest that this training program increased biomechanical economy (as defined by propulsive moment) without increasing shoulder or elbow joint stresses.     

Manual wheelchair pushrim biomechanics and axle position

OBJECTIVE: The biomechanics of wheelchair propulsion have been linked to upper extremity injury. Specifically, prior studies have correlated increased median nerve dysfunction with increasing propulsion frequency and a higher rate of rise of the resultant, or total, pushrim force. Despite this link, there is little research on the effect of wheelchair setup on propulsion biomechanics. The objective of this study was to determine the effect of rear axle position relative to the shoulder on pushrim biomechanics. DESIGN: Case series. SETTING: Biomechanics laboratory. PARTICIPANTS: Forty individuals with paraplegia who use manual wheelchairs for mobility. INTERVENTION: Subjects propelled their own wheelchairs on a dynamometer at two different steady-state speeds and going from a dead stop to maximum speed. Bilateral biomechanical data were obtained using a force- and moment-sensing pushrim and a motion analysis system. MAIN OUTCOME MEASURES: Position of the axle relative to the shoulder at rest both horizontal (XPOS) and vertical (YPOS), and pushrim biomechanical variables including frequency of propulsion, peak and rate of rise of the resultant force, planar moment, and push angle. Partial correlation coefficients between relative axle position and propulsion biomechanics variables were calculated. RESULTS: After controlling for subject characteristics, XPOS was significantly correlated with the frequency of propulsion (p < .01) and the rate of rise of the resultant force (p < .05). In addition, both XPOS and YPOS were significantly correlated with the push angle at multiple speeds (p < .05). CONCLUSION: Specific biomechanical parameters known to correlate with median nerve injuries were found to be related to axle position relative to the shoulder. Providing wheelchair users with adjustable axle position and then fitting the user to the wheelchair can improve propulsion biomechanics and likely reduce the risk of injury.     

Seat height in handrim wheelchair propulsion

To study the effect of seat height on the cardiorespiratory system and kinematics in handrim wheelchair ambulation, nine non-wheelchair users participated in a wheelchair exercise experiment on a motor-driven treadmill. The subjects conducted five progressive exercise tests. After an initial try-out test, four tests were performed at different standardized seat heights of 100, 120, 140, and 160 degrees elbow extension (subject sitting erect, hands on the rim in top-dead-center = 12.00 hrs; full extension = 180 degrees). Each test consisted of four 3-minute exercise blocks at speeds of respectively 0.55, 0.83, 1.11, and 1.39 m.s-1 (2-5 km.hr-1). Analysis of variance revealed significant effects of seat height (P less than 0.05) on gross mechanical efficiency (ME), oxygen cost, push range, and push duration, and on the ranges of motion in the different arm segments and trunk. Mean ME appeared higher at the lower seat heights of 100 and 120 degrees elbow extension. This is reflected in an enhanced oxygen consumption at seat heights of 140 and 160 degrees elbow extension. Simultaneously, the push range showed a 15 to 20 degree decrease with increasing seat height, which is reflected in a decreased push duration. In the push phase, decreases in retroflexion and abduction/adduction of the upper arm were seen. The trunk shifted further forward, and the motion range in the elbow joint shifted to extension with increasing seat height. No shifts in minimum and maximum angular velocities were seen with increasing seat height. The results showed an interrelationship between wheelchair seat height and both cardiorespiratory and kinematic parameters. With respect to the cardiorespiratory system, the optimization of the wheelchair geometry, based on functional characteristics of the user, appears beneficial.     

Effect of system tilt and seat-to-backrest angles on load sustained by shoulder during wheelchair propulsion

This study determined the effect of system tilt angle (STA) and seat-to-backrest angle (SBA) changes on the load sustained by the shoulder during manual wheelchair propulsion. Fourteen elderly participants (mean +/- standard deviation age 68.2 +/- 5.2 years) were recruited. Combinations of three STAs (0 degrees , 5 degrees , and 10 degrees ) and three SBAs (95 degrees , 100 degrees , and 105 degrees ) were randomly tested. The initial position of the wheel axle was held constant with respect to the participant's shoulder position in each condition (horizontal: 4 cm forward of shoulder, vertical: 110 degrees to 120 degrees elbow extension). The shoulder load was estimated by the joint moments. The analysis did not reveal any significant differences between shoulder joint moments (average and peak) for the various STA and SBA combinations. Changing the seat angle while keeping the wheel-axle position constant maintained the shoulder load at the same level. Thus, seat angle can be determined with the goals of user comfort and pressure modulation at the seat interface for alleviating pressure ulcers without increasing risk of overuse shoulder injuries.     

Shoulder kinematics and kinetics during two speeds of wheelchair propulsion

The primary objective of this study was to examine the kinematics and kinetics of the shoulder during wheelchair propulsion at a slow and moderate speed. Twenty-seven individuals with paraplegia propelled their wheelchairs at speeds of 0.9 m/s and 1.8 m/s while a motion analysis system captured movements of their upper limbs and SMART(Wheel)s simultaneously recorded their pushrim kinetics. Intraclass R correlation and Cronbach's coefficient alpha statistics revealed that all shoulder parameters were stable and consistent between strokes and speeds. The shoulder exhibited a greater range of motion, and forces and moments at the shoulder were 1.2 to 2.0 times greater (p < 0.05) during the 1.8 m/s speed trial. Peak posterior forces occurred near the end of the propulsion phase, and at the same time, the shoulder was maximally flexed and minimally abducted (p > 0.1). Shoulder positioning and the associated peak shoulder loads during propulsion may be important indicators for identifying manual wheelchair users at risk for developing shoulder pain and injury.     

Effect of different hand positions on trunk and shoulder kinematics and reaction forces in sitting pivot transfer

[Purpose] The purpose of this study was to compare the changes in trunk and shoulder angles, and reaction forces under the two hands elicited by different hand base of support positions during sitting pivot transfer. [Subjects and Methods] Eighteen unimpaired subjects performed independent sitting pivot transfer. Subjects performed sitting pivot transfer between an initial seat to a target seat by only using their hands positioned at the same height as and lower than the seat position. Trunk and shoulder kinematics, and reaction forces on the trailing and leading hands were calculated. Mean peak joint angles and forces were compared between the hand positions using the pared t-test for the lift phase of the transfer. [Results] There were significant increases in the trunk angles of forward and lateral flexion, even though rotation decreased while transferring in the lower hand position. Increased shoulder flexion, anterior/posterior forces and reduced lateral forces were also shown. [Conclusion] Placing the hands of the supporting arms lower than the seat position during sitting pivot transfer was identified as having biomechanical advantages. Therefore, the lower hand position can be recommended as an effective and safe method for sitting pivot transfer by patients with spinal cord injury and can be utilized as a reference data for considering the appropriate height of aids for a wheelchair.Key words: Hand position, Sitting pivot transfer, Shoulder pain     

The effect of rear-wheel position on seating ergonomics and mobility efficiency in wheelchair users with spinal cord injuries: a pilot study

This study analyzed the effect of rear-wheel position on seating comfort and mobility efficiency. Twelve randomly selected paraplegic wheelchair users participated in the study. Wheelchairs were tested in two rear-wheel positions while the users operated the wheelchair on a treadmill and while they worked on a computer. Propulsion efficiency, seating comfort, and propulsion qualities were registered at different loads during the treadmill session. During the computer session, pelvic position, estimated seating comfort, and estimated activity performance were measured. The change in rear-wheel position affected wheelchair ergonomics with respect to weight distribution (p < 0.0001) and seat inclination angle (position I = 5 and position II = 12). These changes had a significant effect on push frequency (p < 0.05) and stroke angle (p < 0.05) during wheelchair propulsion. We found no consistent effect on mechanical efficiency, estimated exertion, breathlessness, seating comfort, estimated propulsion qualities, pelvic position, or activity performance.     

Scapula kinematics and associated impingement risk in manual wheelchair users during propulsion and a weight relief lift

Background

Shoulder impingement syndrome is a common upper extremity pathology in manual wheelchair users. Central to impingement is the orientation of the scapula and humerus as they determine the available subacromial space. The purpose of this study was to examine the scapulothoracic and glenohumeral internal/external rotation kinematics during the time of peak shoulder loading of propulsion and weight relief lift conditions to assess possible risk of impingement.

Methods

Scapula, humerus and trunk kinematics were measured for twelve manual wheelchair users over three conditions: level propulsion, ramp propulsion, and a weight relief lift. Scapulothoracic and glenohumeral kinematic variables were characterized for the full cycle of each condition as well as at the period of peak loading.

Findings

Common to all activities was an externally rotated glenohumeral joint and an anteriorly tilted and internally rotated scapula. At peak loading, glenohumeral internal/external rotation showed a significant difference between conditions, and post hoc analysis revealed that the weight relief lift displayed significantly less external rotation at peak loading when compared to level and ramp propulsion.

Interpretation

All activities placed the scapula in a potentially dangerous orientation for development of shoulder impingement. The weight relief lift, with a decrease in glenohumeral external rotation and large superior forces at the shoulder, potentially places the shoulder of the manual wheelchair user at the greatest risk for impingement soft tissue injury. Preventative strength training and activity modification may provide measures to slow progression of impingement development and associated pain in the manual wheelchair user.     

A theoretical analysis of the influence of wheelchair seat position on upper extremity demand

Background

The high physical demands placed on the upper extremity during manual wheelchair propulsion can lead to pain and overuse injuries that further reduce user independence and quality of life. Seat position is an adjustable parameter that can influence the mechanical loads placed on the upper extremity. The purpose of this study was to use a musculoskeletal model and forward dynamics simulations of wheelchair propulsion to identify the optimal seat position that minimizes various measures of upper extremity demand including muscle stress, co-contraction and metabolic cost.

Methods

Forward dynamics simulations of wheelchair propulsion were generated across a range of feasible seat positions by minimizing the change in handrim forces and muscle-produced joint moments. Resulting muscle stress, co-contraction and metabolic cost were examined to determine the optimal seat position that minimized these values.

Findings

Muscle stress and metabolic cost were near minimal values at superior/inferior positions corresponding to top-dead-center elbow angles between 110 and 120° while at an anterior/posterior position with a hub-shoulder angle between − 10 and − 2.5°. This coincided with a reduction in the level of muscle co-contraction, primarily at the glenohumeral joint.

Interpretation

Deviations from this position lead to increased co-contraction to maintain a stable, smooth propulsive stroke, which consequentially increases upper extremity demand. These results agree with previous clinical guidelines for positioning the seat to reduce upper extremity overuse injuries and pain for wheelchair users.     

Upper-limb joint power and its distribution in spinal cord injured wheelchair users: steady-state self-selected speed versus maximal acceleration trials

OBJECTIVE: To compare upper-limb joint power magnitude and distribution between the shoulder, elbow, and wrist during maximal acceleration (MAC) versus steady-state, self-selected speed (SSS) manual wheelchair propulsion. DESIGN: Cross-sectional biomechanic study. SETTING: Research university and teaching hospital. PARTICIPANTS: Volunteer sample of 13 manual wheelchair users with spinal cord injury below T1. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Propulsive joint power magnitude and fractional distribution among upper-limb joints. RESULTS: Wilcoxon signed-rank testing revealed shoulder power was larger for MAC versus SSS (median peak, 101.5W; interquartile range [IQR], 74.6; median peak, 37.7W; IQR, 22.9; respectively) (P<.01). Elbow and wrist power were unchanged. Peak shoulder power fraction was larger for MAC versus SSS (median peak, 1.055; IQR, .110 vs peak, .870; IQR, .252) (P<.01). Peak elbow power fraction was smaller for MAC versus SSS (median peak, -.012; IQR, .144 vs peak, .146; IQR, .206) (P<.05). Peak wrist power fraction was smaller for MAC versus SSS (median peak, -.058; IQR, .057 vs peak, -.010; IQR, .150) (P<.05). CONCLUSIONS: Power at the shoulder was larger than at other joints. Peak shoulder joint power and power fraction was larger during MAC versus SSS propulsion. Elbow and wrist power fractions were smaller for MAC versus SSS propulsion. Higher joint power, present under MAC, may predispose manual wheelchair users to injury, particularly at the shoulder.     

The influence of operator and wheelchair factors on wheelchair propulsion effort

Abstract

Purpose: The goal of this study was to evaluate the relative influence of operator and wheelchair factors on propulsion effort during over-ground wheelchair manoeuvres.

Method: This observational study included 23 full-time manual wheelchair users and 13 able-bodied subjects. The operator factors included shoulder position, aerobic capacity and propulsion strength. The wheelchair factors included system mass, weight distribution, and frictional loss in straight and turning trajectories. The performance of over-ground manoeuvres was defined as the propulsion effort measured by VO₂ as operators propelled along a modified figure-8 course on tile and carpet surfaces.

Results: According to our regression model, shoulder position was the only significant contributor within operator factors, whereas weight distribution was the only significant contributor within wheelchair factors in influencing propulsion efforts. When combining operator and mechanical factors in the regression model, weight distribution became the only significant contributor to influence propulsion effort.

Conclusion: Weight distribution and shoulder position had a significant influence on propulsion effort. These variables are related to the operator’s relationship to the drive wheels. However, system mass and muscle strength had the least influence on wheelchair manoeuvres. Our finding can help clinicians to improve wheelchair configurations and manufacturers to improve wheelchair design by understanding the importance of shoulder position and weight distribution.

• Implication for rehabilitation

• Studying wheelchair manoeuvers by considering both wheelchair and operator factors might provide a unique insight to address the complex interactions among wheelchair designs and users.

• Propulsion effort decreases as percentage weight is increased on the drive wheels and the shoulder becomes more aligned with the axle position, which highlights the need to optimize wheelchair axle position.

• Wheelchair configuration, as represented by weight distribution, had a more significant influence on everyday manoeuvre than wheelchair mass does.

• It is essential for wheelchair users to choose a wheelchair that can match their daily needs and anthropometric measurements for saving propulsion efforts.

     

Wrist kinematic characterization of wheelchair propulsion in various seating positions: implication to wrist pain

OBJECTIVE: To investigate wrist kinematic characterization at various wheelchair seat positions. DESIGN: A comparative study using a repetitive measures design. BACKGROUND: People who use wheelchairs often sit on pressure-relief cushions, increasing the seat height. Wrist kinematic properties during manual propulsion could be altered. Wrist kinematics from a clinical perspective has not been previously investigated. This study characterizes wrist kinematic performance of subjects during manual wheelchair propulsion at various seat positions. METHODS: Subjects for this investigation were 11 people with disabilities who use wheelchairs. Combinations of horizontal positions of the rear wheel and vertical seat height were evaluated. Consecutive EMG, wrist joint angle, and trigger signals were collected. RESULTS: Altered seat height resulted in significant changes to temporal phases and wrist kinematic parameters; however, altered horizontal seat position did not cause significant variations. For all seat positions investigated, wrist extensor and flexor EMG signals maintained a similar level of contraction. CONCLUSION: During wheelchair propulsion, seat height was found to be a critical factor affecting the temporal parameters of movement and wrist kinematic properties of the subjects. Wrist joint angles and wrist flexion-extension range of motion all varied according to seat height. Observations and statistical analysis of the results provided useful information; however, an ideal seat position was not indicated. RELEVANCE: Study results have enhanced our understanding of wheelchair design, and should aid in development of future designs. In addition, the results may provide a strategy for dealing with the onset of arm/wrist pain and the prevention of carpal tunnel syndrome and other soft tissue injuries in people who use wheelchairs.