A new method to quantify demand on the upper extremity during manual wheelchair propulsion

Differences in Glenohumeral Joint Contact Forces Between Recovery Hand Patterns During Wheelchair Propulsion With and Without Shoulder Muscle Weakness: A Simulation Study

The majority of manual wheelchair users (MWCU) develop shoulder pain or injuries, which is often caused by impingement. Because propulsion mechanics are influenced by the recovery hand pattern used, the pattern may affect shoulder loading and susceptibility to injury. Shoulder muscle weakness is also correlated with shoulder pain, but how shoulder loading changes with specific muscle group weakness is unknown. Musculoskeletal modeling and simulation were used to compare glenohumeral joint contact forces (GJCFs) across hand patterns and determine how GJCFs vary when primary shoulder muscle groups are weakened. Experimental data were analyzed to classify individuals into four hand pattern groups. A representative musculoskeletal model was then developed for each group and simulations generated to portray baseline strength and six muscle weakness conditions. Three-dimensional GJCF peaks and impulses were compared across hand patterns and muscle weakness conditions. The semicircular pattern consistently had lower shear (anterior-posterior and superior-inferior) GJCFs compared to other patterns. The double-loop pattern had the highest superior GJCFs, while the single-loop pattern had the highest anterior and posterior GJCFs. These results suggest that using the semicircular pattern may be less susceptible to shoulder injuries such as subacromial impingement. Weakening the internal rotators and external rotators resulted in the greatest increases in shear GJCFs and decreases in compressive GJCF, likely due to decreased force from rotator cuff muscles. These findings suggest that strengthening specific muscle groups, especially the rotator cuff, is critical for decreasing the risk of shoulder overuse injuries.

Quantification of the Risk of Musculoskeletal Disorders of the Upper Limb Using Fuzzy Logic: A Study of Manual Wheelchair Propulsion

BACKGROUND

For manual wheelchair users, overuse of the upper limbs can cause upper limb musculoskeletal disorders, which can lead to a loss of autonomy. The main objective of this study was to quantify the risk level of musculoskeletal disorders of different slope propulsions in manual wheelchair users using fuzzy logic.

METHODS

In total, 17 spinal cord injury participants were recruited. Each participant completed six passages on a motorized treadmill, the inclination of which varied between (0° to 4.8°). A motion capture system associated with instrumented wheels of a wheelchair was used. Using a biomechanical model of the upper limb and the fuzzy logic method, an Articular Discomfort Index (ADI) was developed.

RESULTS

We observed an increase in articular discomfort during propulsion on a slope with increasing discomfort at the shoulder, elbow and wrist, due to an increase in kinetics. There was a kinetically significant change in the kinetic global ADI (22 to 25%) and no change in the kinematic. The ADI increased from 14 to 36% during slope propulsion for each joint.

CONCLUSION

The quantification of the level of discomfort helps us to highlight the situations with the most high-risk exposures and to identify the parameters responsible for this discomfort.

Impact of Sprinting and Dribbling on Shoulder Joint and Pushrim Kinetics in Wheelchair Basketball Athletes

Background

While wheelchair basketball is one of the most popular Paralympic sports, it eventually causes shoulder problems and pain in many athletes. However, shoulder kinetics has never been assessed during propulsion in wheelchair basketball. This study analyzes the impact of sprinting and dribbling on pushrim and shoulder kinetics in terms of external forces and net muscular moments.

Methods

A group of 10 experienced wheelchair basketball athletes with various classifications performed four, 9-m sprints on a basketball court using classic synchronous propulsion, and four sprints while dribbling forward. Pushrim and shoulder kinetics were calculated by inverse dynamics, using a motion capture device and instrumented wheels.

Findings

Sprinting was associated to peak shoulder load from 13 to 346% higher than in previous studies on standard wheelchair propulsion in most force/moment components. Compared to sprinting without a ball, dribbling reduced the speed, the peak external forces in the anterior and medial direction at the shoulder, and the peak net shoulder moment of internal rotation.

Interpretation

The high shoulder load calculated during both sprinting and dribbling should be considered during training sessions to avoid overloading the shoulder. Dribbling generally reduced the shoulder load, which suggests that propelling while dribbling does not put the shoulder at more risk of musculoskeletal disorders than sprinting.

Glenohumeral joint dynamics and shoulder muscle activity during geared manual wheelchair propulsion on carpeted floor in individuals with spinal cord injury

This study investigated the effects of using geared wheels on glenohumeral joint dynamics and shoulder muscle activity during manual wheelchair propulsion. Seven veterans with spinal cord injury propelled their wheelchairs equipped with geared wheels over a carpeted floor in low gear (1.5:1) and standard gear (1:1) conditions. Hand-rim kinetics, glenohumeral joint dynamics, and muscle activity were measured using a custom instrumented geared wheel, motion analysis, and surface electromyography. Findings indicated that the propulsion speed and stroke distance decreased significantly during the low gear condition. The peak hand-rim resultant force and propulsive moment, as well as the peak glenohumeral inferior force and flexion moment, were significantly less during the low gear condition. The peak and integrated muscle activity of the anterior deltoid and pectoralis major decreased significantly, while the normalized integrated muscle activity (muscle activity per stroke distance) was not significantly different between the two conditions. Propulsion on carpeted floor in the low gear condition was accompanied by a reduced perception of effort. The notable decrease in the peak shoulder loading and muscle activity suggests that usage of geared wheels may be beneficial for wheelchair users to enhance independent mobility in their homes and communities while decreasing their shoulder demands.

Relationship Between Shoulder Pain and Joint Reaction Forces and Muscle Moments During 2 Speeds of Wheelchair Propulsion

The purpose of this study was to determine shoulder joint reaction forces and muscle moments during 2 speeds (1.3 and 2.2 m/s) of wheelchair propulsion and to investigate the relationship between joints reaction forces, muscle moments, and shoulder pain. The measurements were obtained from 20 manual wheelchair users. A JR3 6-channel load sensor (±1% error) and a Qualisys system were used to record 3-dimensional pushrim kinetics and kinematics. A 3-dimensional inverse dynamic model was generated to compute joint kinetics. The results demonstrated significant differences in shoulder joint forces and moments (P < .01) between the 2 speeds of wheelchair propulsion. The greatest peak shoulder joint forces during the drive phase were anterior directed (Fy, 184.69 N), and the greatest joint moment was the shoulder flexion direction (flexion moment, 35.79 N·m) at 2.2 m/s. All the shoulder joint reaction forces and flexion moment were significantly (P < .05) related to shoulder pain index. The forces combined in superior and anterior direction found at the shoulder joint may contribute to the compression of subacromial structure and predispose manual wheelchair users to potential rotator cuff impingement syndrome.

A comparison of glenohumeral joint kinematics and muscle activation during standard and geared manual wheelchair mobility

The high prevalence of upper extremity joint injuries among manual wheelchair users is largely attributed to the high repetitive loading during propulsion. The purpose of this study was to evaluate the effects of using geared wheels for manual wheelchair mobility on shoulder joint biomechanics. Fourteen able-bodied participants performed overground propulsion and ramp ascension using standard and geared manual wheelchair wheels. Spatial temporal parameters, glenohumeral joint kinematics, and shoulder muscle activity were quantified. Findings indicated that regardless of the level of slope, the propulsion speed and stroke distance decreased significantly (p ≪ 0.001), and the stroke frequency increased significantly (p ≤ 0.025) during geared manual wheelchair propulsion. The glenohumeral joint ranges of motion in the coronal plane (p ≤ 0.005) and peak joint angles in the coronal (p ≤ 0.023) and transverse (p ≤ 0.012) planes were significantly different between standard and geared wheels usage. Shoulder muscle activity was substantially less using the geared wheels with significant findings in the pectoralis major (level floor, p ≤ 0.008) and infraspinatus (p ≤ 0.014) peak muscle activity, and the anterior deltoid (p ≤ 0.014) and pectoralis major (p ≤ 0.015) integrated muscle activity. However, the shoulder flexor normalized integrated muscle activity (muscle activity per stroke distance) was not different between the wheels.

Comparison of shoulder kinematic chain models and their influence on kinematics and kinetics in the study of manual wheelchair propulsion

Several kinematic chains of the upper limbs have been designed in musculoskeletal models to investigate various upper extremity activities, including manual wheelchair propulsion. The aim of our study was to compare the effect of an ellipsoid mobilizer formulation to describe the motion of the scapulothoracic joint with respect to regression-based models on shoulder kinematics, shoulder kinetics and computational time, during manual wheelchair propulsion activities. Ten subjects, familiar with manual wheelchair propulsion, were equipped with reflective markers and performed start-up and propulsion cycles with an instrumented field wheelchair. Kinematic data obtained from the optoelectronic system and kinetic data measured by the sensors on the wheelchair were processed using the OpenSim software with three shoulder joint modeling versions (ellipsoid mobilizer, regression equations or fixed scapula) of an upper-limb musculoskeletal model. As expected, the results obtained with the three versions of the model varied, for both segment kinematics and shoulder kinetics. With respect to the model based on regression equations, the model describing the scapulothoracic joint as an ellipsoid could capture the kinematics of the upper limbs with higher fidelity. In addition, the mobilizer formulation allowed to compute consistent shoulder moments at a low computer processing cost. Further developments should be made to allow a subject-specific definition of the kinematic chain.

Predictors of shoulder pain in manual wheelchair users

BACKGROUND

Manual wheelchair users rely on their upper limbs to provide independent mobility, which leads to high muscular demand on their upper extremities and often results in shoulder pain and injury. However, the specific causes of shoulder pain are unknown. Previous work has shown that decreased shoulder muscle strength is predictive of shoulder pain onset, and others have analyzed joint kinematics and kinetics, propulsion technique and intra-individual variability for their relation to shoulder pathology. The purpose of this study was to determine in a longitudinal setting whether there are specific biomechanical measures that predict shoulder pain development in manual wheelchair users.

METHODS

All participants were asymptomatic for shoulder pain and categorized into pain and no pain groups based on assessments at 18 and 36 months later. Shoulder strength, handrim and joint kinetics, kinematics, spatiotemporal measures, intra-individual standard deviations and coefficients of variation were evaluated as predictors of shoulder pain.

FINDINGS

Individuals who developed shoulder pain had weaker shoulder adductor muscles, higher positive shoulder joint work during recovery, and less trunk flexion than those who did not develop pain. In addition, relative intra-individual variability was a better predictor of shoulder pain than absolute variability, however future work is needed to determine when increased versus decreased variability is more favorable for preventing shoulder pain.

INTERPRETATION

These predictors may provide insight into how to improve rehabilitation training and outcomes for manual wheelchair users and ultimately decrease their likelihood of developing shoulder pain and injuries.

Engineering and Technology in Wheelchair Sport

Technologies capable of projecting injury and performance metrics to athletes and coaches are being developed. Wheelchair athletes must be cognizant of their upper limb health; therefore, systems must be designed to promote efficient transfer of energy to the handrims and evaluated for simultaneous effects on the upper limbs. This article is brief review of resources that help wheelchair users increase physiologic response to exercise, develop ideas for adaptive workout routines, locate accessible facilities and outdoor areas, and develop wheelchair sports-specific skills.

Assessment of a markerless motion analysis system for manual wheelchair application

BACKGROUND

Wheelchair biomechanics research advances accessibility and clinical care for manual wheelchair users. Standardized outcome assessments are vital tools for tracking progress, but there is a strong need for more quantitative methods. A system offering kinematic, quantitative detection, with the ease of use of a standardized outcome assessment, would be optimal for repeated, longitudinal assessment of manual wheelchair users' therapeutic progress, but has yet to be offered.

RESULTS

This work evaluates a markerless motion analysis system for manual wheelchair mobility in clinical, community, and home settings. This system includes Microsoft® Kinect® 2.0 sensors, OpenSim musculoskeletal modeling, and an automated detection, processing, and training interface. The system is designed to be cost-effective, easily used by caregivers, and capable of detecting key kinematic metrics involved in manual wheelchair propulsion. The primary technical advancements in this research are the software components necessary to detect and process the upper extremity kinematics during manual wheelchair propulsion, along with integration of the components into a complete system. The study defines and evaluates an adaptable systems methodology for processing kinematic data using motion capture technology and open-source musculoskeletal models to assess wheelchair propulsion pattern and biomechanics, and characterizes its accuracy, sensitivity and repeatability. Inter-trial repeatability of spatiotemporal parameters, joint range of motion, and musculotendon excursion were all found to be significantly correlated (p < 0.05).

CONCLUSIONS

The system is recommended for use in clinical settings for frequent wheelchair propulsion assessment, provided the limitations in precision are considered. The motion capture-model software bridge methodology could be applied in the future to any motion-capture system or specific application, broadening access to detailed kinematics while reducing assessment time and cost.

Kinematics and pushrim kinetics in adolescents propelling high-strength lightweight and ultra-lightweight manual wheelchairs

PURPOSE

The purpose of this study is to describe and compare pushrim forces, propulsive work cost, and upper body kinematics in adolescents propelling (1) a standard high strength lightweight wheelchair, and (2) an ultra-lightweight wheelchair with adjustable main axle positioning, on a level tiled floor ("Tile"), ascending a ramp ("Ramp"), and across a foam mat ("Mat").

METHODS

A within-subjects repeated measures study design was used. Eight adolescent manual wheelchair users propelled the standard and ultra-lightweight wheelchairs across the three conditions. Average pushrim tangential force, propulsive power and work per unit distance travelled, as well as upper body kinematic angles, were analyzed.

RESULTS

Average pushrim tangential force (1.80 ± 0.7 N, p = .042) and propulsive work per unit distance travelled (8.3 ± 1.7 J·m^{- 1}, p = .002) were higher for the standard lightweight wheelchair, whereas average speed was lower (0.12 ± 0.03 m/s, p = .006). Maximum shoulder (9.2 ± 2.0°, p = .003) and elbow flexion (8.0 ± 2.2°, p = .009) were higher for the ultra-lightweight wheelchair. Compared with Tile, propulsion on Mat and Ramp was associated with higher average tangential force, work per unit distance, power, and maximum flexion of the neck and trunk, whereas shoulder extension and average speed were lower for Mat and Ramp.

CONCLUSIONS

Compared with the standard lightweight wheelchair, ultra-lightweight wheelchair propulsion was associated with lower pushrim forces, lower energy costs, higher self-selected speeds, and increased shoulder and elbow flexion. These variables have been linked to injury risk and mobility efficiency, and the results provided evidence that differences in weight and configuration options are both contributors. Findings can inform decision-making in the prescription of manual wheelchairs for pre-adult populations. Implications for Rehabilitation A significant proportion of manual wheelchair users are children and adolescents, and due to the early onset of use they may be especially predisposed to the development of chronic overuse injuries. The study reports differences in energy costs, pushrim forces, and upper body kinematics measured when adolescents propelled standard and ultra-lightweight wheelchairs across three trial conditions. In the ultra-lightweight wheelchair, reduced energy cost is linked to more efficient mobility, and lower forces may be linked to lower risk of chronic injury. Significant differences in elbow and shoulder kinematics are also reported, and the findings support the importance of both weight and setup options in the selection of manual wheelchairs.

Effects of Seated Postural Stability and Trunk and Upper Extremity Strength on Performance during Manual Wheelchair Propulsion Tests in Individuals with Spinal Cord Injury: An Exploratory Study

Objectives. To quantify the association between performance-based manual wheelchair propulsion tests (20 m propulsion test, slalom test, and 6 min propulsion test), trunk and upper extremity (U/E) strength, and seated reaching capability and to establish which ones of these variables best predict performance at these tests. Methods. 15 individuals with a spinal cord injury (SCI) performed the three wheelchair propulsion tests prior to discharge from inpatient SCI rehabilitation. Trunk and U/E strength and seated reaching capability with unilateral hand support were also measured. Bivariate correlation and multiple linear regression analyses allowed determining the best determinants and predictors, respectively. Results. The performance at the three tests was moderately or strongly correlated with anterior and lateral flexion trunk strength, anterior seated reaching distance, and the shoulder, elbow, and handgrip strength measures. Shoulder adductor strength-weakest side explained 53% of the variance on the 20-meter propulsion test-maximum velocity. Shoulder adductor strength-strongest side and forward seated reaching distance explained 71% of the variance on the slalom test. Handgrip strength explained 52% of the variance on the 6-minute propulsion test. Conclusion. Performance at the manual wheelchair propulsion tests is explained by a combination of factors that should be considered in rehabilitation.

The influence of wheelchair propulsion hand pattern on upper extremity muscle power and stress

The hand pattern (i.e., full-cycle hand path) used during manual wheelchair propulsion is frequently classified as one of four distinct hand pattern types: arc, single loop, double loop or semicircular. Current clinical guidelines recommend the use of the semicircular pattern, which is based on advantageous levels of broad biomechanical metrics implicitly related to the demand placed on the upper extremity (e.g., lower cadence). However, an understanding of the influence of hand pattern on specific measures of upper extremity muscle demand (e.g., muscle power and stress) is needed to help make such recommendations, but these quantities are difficult and impractical to measure experimentally. The purpose of this study was to use musculoskeletal modeling and forward dynamics simulations to investigate the influence of the hand pattern used on specific measures of upper extremity muscle demand. The simulation results suggest that the double loop and semicircular patterns produce the most favorable levels of overall muscle stress and total muscle power. The double loop pattern had the lowest full-cycle and recovery-phase upper extremity demand but required high levels of muscle power during the relatively short contact phase. The semicircular pattern had the second-lowest full-cycle levels of overall muscle stress and total muscle power, and demand was more evenly distributed between the contact and recovery phases. These results suggest that in order to decrease upper extremity demand, manual wheelchair users should consider using either the double loop or semicircular pattern when propelling their wheelchairs at a self-selected speed on level ground.

Compensatory strategies during manual wheelchair propulsion in response to weakness in individual muscle groups: A simulation study

BACKGROUND

The considerable physical demand placed on the upper extremity during manual wheelchair propulsion is distributed among individual muscles. The strategy used to distribute the workload is likely influenced by the relative force-generating capacities of individual muscles, and some strategies may be associated with a higher injury risk than others. The objective of this study was to use forward dynamics simulations of manual wheelchair propulsion to identify compensatory strategies that can be used to overcome weakness in individual muscle groups and identify specific strategies that may increase injury risk. Identifying these strategies can provide rationale for the design of targeted rehabilitation programs aimed at preventing the development of pain and injury in manual wheelchair users.

METHODS

Muscle-actuated forward dynamics simulations of manual wheelchair propulsion were analyzed to identify compensatory strategies in response to individual muscle group weakness using individual muscle mechanical power and stress as measures of upper extremity demand.

FINDINGS

The simulation analyses found the upper extremity to be robust to weakness in any single muscle group as the remaining groups were able to compensate and restore normal propulsion mechanics. The rotator cuff muscles experienced relatively high muscle stress levels and exhibited compensatory relationships with the deltoid muscles.

INTERPRETATION

These results underline the importance of strengthening the rotator cuff muscles and supporting muscles whose contributions do not increase the potential for impingement (i.e., the thoracohumeral depressors) and minimize the risk of upper extremity injury in manual wheelchair users.

Relationship between maximum isometric joint moment and functional task performance in patients with brachial plexus injury: A pilot study

We evaluated whether subjects with brachial plexus injury (BPI) adapted their movements to reduce the mechanical demand on their impaired upper extremity. In 6 subjects with unilateral BPI with C5 and C6 involvement, we measured bilateral maximum isometric shoulder and elbow strength, and computed joint kinematics and net muscle-generated joint moments during 7 unimanual functional tasks. Compared to the unimpaired extremity, maximum strength in shoulder abduction, extension, and external rotation was 60% (p=0.02), 49% (p=0.02), and 75% (p=0.02) lower, respectively, on the impaired side. Significant kinematic and kinetic differences were observed only when reaching to the back of the head. However, because of substantially reduced strength in their impaired upper extremities, subjects used a significantly higher percentage of their maximum strength during several tasks and along several directions of movement. The peak percentage of maximal strength subjects used across tasks was 32% (p=0.03) and 29% (p=0.03) more on their impaired side in shoulder extension and external rotation, respectively. Subjects had less reserve strength available for performing upper extremity tasks and, therefore, may be less adaptive to strength declines due to injury progression and normal aging. Quantitatively measuring maximal strength may help clinicians ensure that patients maintain sufficient upper extremity strength to preserve long-term functional ability.

Shoulder Strength and Physical Activity Predictors of Shoulder Pain in People With Paraplegia From Spinal Injury: Prospective Cohort Study

BACKGROUND

Shoulder joint pain is a frequent secondary complaint for people following spinal cord injury (SCI).

OBJECTIVE

The purpose of this study was to determine predictors of shoulder joint pain in people with paraplegia.

METHODS/DESIGN

A 3-year longitudinal study was conducted. Participants were people with paraplegia who used a manual wheelchair for at least 50% of their mobility and were asymptomatic for shoulder pain at study entry. Participants were classified as having developed shoulder pain if they experienced an increase of ≥10 points on the Wheelchair User's Shoulder Pain Index in the 3-year follow-up period. Measurements of maximal isometric shoulder torques were collected at study entry (baseline), 18 months, and 3 years. Daily activity was measured using a wheelchair odometer, and self-reported daily transfer and raise frequency data were collected by telephone every 6 weeks.

RESULTS

Two hundred twenty-three participants were enrolled in the study; 39.8% developed shoulder pain over the 3-year follow-up period. Demographic variables and higher activity levels were not associated with shoulder pain onset. Baseline maximal isometric torque (normalized by body weight) in all shoulder muscle groups was 10% to 15% lower in participants who developed shoulder pain compared with those who remained pain-free. Lower shoulder adduction torque was a significant predictor of shoulder pain development (log-likelihood test=11.38), but the model explained only 7.5% of shoulder pain onset and consequently is of limited clinical utility.

LIMITATIONS

Time since SCI varied widely among participants, and transfer and raise activity was measured by participant recall.

CONCLUSIONS

Participants who developed shoulder pain had decreased muscle strength, particularly in the shoulder adductors, and lower levels of physical activity prior to the onset of shoulder pain. Neither factor was a strong predictor of shoulder pain onset.

Pushrim biomechanical changes with progressive increases in slope during motorized treadmill manual wheelchair propulsion in individuals with spinal cord injury

The purpose of this study was to quantify the effects of five distinct slopes on spatiotemporal and pushrim kinetic measures at the nondominant upper limb during manual wheelchair (MWC) propulsion on a motorized treadmill in individuals with spinal cord injury (SCI). Eighteen participants with SCI propelled their MWC at a self-selected natural speed on a treadmill at different slopes (0, 2.7, 3.6, 4.8, and 7.1 degrees). Spatiotemporal parameters along with total force and tangential components of the force applied to the pushrim, including mechanical effective force, were calculated using an instrumented wheel. The duration of the recovery phase was 54% to 70% faster as the slope increased, whereas the duration of the push phase remained similar. The initial contact angles migrated forward on the pushrim, while the final and total contact angles remained similar as the slope increased. As the slope increased, the mean total force was 93% to 201% higher and the mean tangential component of the force was 96% to 176% higher than propulsion with no slope. Measures were similar for the 2.7 and 3.6 degrees slopes. Overall, the recovery phase became shorter and the forces applied at the pushrim became greater as the slope of the treadmill increased during motorized treadmill MWC propulsion.

The influence of wheelchair propulsion technique on upper extremity muscle demand: a simulation study

BACKGROUND

The majority of manual wheelchair users will experience upper extremity injuries or pain, in part due to the high force requirements, repetitive motion and extreme joint postures associated with wheelchair propulsion. Recent studies have identified cadence, contact angle and peak force as important factors for reducing upper extremity demand during propulsion. However, studies often make comparisons between populations (e.g., able-bodied vs. paraplegic) or do not investigate specific measures of upper extremity demand. The purpose of this study was to use a musculoskeletal model and forward dynamics simulations of wheelchair propulsion to investigate how altering cadence, peak force and contact angle influence individual muscle demand.

METHODS

Forward dynamics simulations of wheelchair propulsion were generated to emulate group-averaged experimental data during four conditions: 1) self-selected propulsion technique, and while 2) minimizing cadence, 3) maximizing contact angle, and 4) minimizing peak force using biofeedback. Simulations were used to determine individual muscle mechanical power and stress as measures of muscle demand.

RESULTS

Minimizing peak force and cadence had the lowest muscle power requirements. However, minimizing peak force increased cadence and recovery power, while minimizing cadence increased average muscle stress. Maximizing contact angle increased muscle stress and had the highest muscle power requirements.

INTERPRETATION

Minimizing cadence appears to have the most potential for reducing muscle demand and fatigue, which could decrease upper extremity injuries and pain. However, altering any of these variables to extreme values appears to be less effective; instead small to moderate changes may better reduce overall muscle demand.

Relationship of physical therapy inpatient rehabilitation interventions and patient characteristics to outcomes following spinal cord injury: the SCIRehab project

BACKGROUND/OBJECTIVE

Examine associations of type and quantity of physical therapy (PT) interventions delivered during inpatient spinal cord injury (SCI) rehabilitation and patient characteristics with outcomes at the time of discharge and at 1 year post-injury.

METHODS

Physical therapists delivering routine care documented details of PT interventions provided. Regression modeling was used to predict outcomes at discharge and 1 year post-injury for a 75% subset; models were validated with the remaining 25%. Injury subgroups also were examined: motor complete low tetraplegia, motor complete paraplegia, and American Spinal Injury Association (ASIA) Impairment Scale (AIS) D motor incomplete tetra-/paraplegia.

RESULTS

PT treatment variables explain more variation in three functionally homogeneous subgroups than in the total sample. Among patients with motor complete low tetraplegia, higher scores for the transfer component of the discharge motor Functional Independence Measure () are strongly associated with more time spent working on manual wheelchair skills. Being male is the most predictive variable for the motor FIM score at discharge for patients with motor complete paraplegia. Admission ASIA lower extremity motor score (LEMS) and change in LEMS were the factors most predictive for having the primary locomotion mode of "walk" or "both (walk and wheelchair)" on the discharge motor FIM for patients with AIS D injuries.

CONCLUSION

Injury classification influences type and quantity of PT interventions during inpatient SCI rehabilitation and is a strong predictor of outcomes at discharge and 1 year post-injury. The impact of PT treatment increases when patient groupings become more homogeneous and outcomes become specific to the groupings. Note: This is the second of nine articles in the SCIRehab series.

BIOMECHANICS OF WHEELCHAIR PROPULSION

With progress of modern technology, manually-propelled wheelchairs are still of importance for individuals with mobility impairments. The repeated wheelchair propulsion and strenuous daily activities cause high loads and thus injuries on the upper extremity joints. Over the past few years, a considerable number of studies have been made on biomechanical analysis of wheelchair propulsion and wheelchair-related activities. Thorough investigation of biomechanics during wheelchair propulsion enhances comprehension of mechanism of injuries and provides information to improve wheelchair design and fitting. Numerous investigations have been made to demonstrate factors which cause low effectiveness of force application and inefficiency of movements. Emphasis was also placed on developing analytical models to simulate wheelchair propulsion.

Individual muscle contributions to push and recovery subtasks during wheelchair propulsion

Manual wheelchair propulsion places considerable physical demand on the upper extremity and is one of the primary activities associated with the high prevalence of upper extremity overuse injuries and pain among wheelchair users. As a result, recent effort has focused on determining how various propulsion techniques influence upper extremity demand during wheelchair propulsion. However, an important prerequisite for identifying the relationships between propulsion techniques and upper extremity demand is to understand how individual muscles contribute to the mechanical energetics of wheelchair propulsion. The purpose of this study was to use a forward dynamics simulation of wheelchair propulsion to quantify how individual muscles deliver, absorb and/or transfer mechanical power during propulsion. The analysis showed that muscles contribute to either push (i.e., deliver mechanical power to the handrim) or recovery (i.e., reposition the arm) subtasks, with the shoulder flexors being the primary contributors to the push and the shoulder extensors being the primary contributors to the recovery. In addition, significant activity from the shoulder muscles was required during the transition between push and recovery, which resulted in increased co-contraction and upper extremity demand. Thus, strengthening the shoulder flexors and promoting propulsion techniques that improve transition mechanics have much potential to reduce upper extremity demand and improve rehabilitation outcomes.

Wheelchair ramp navigation in snow and ice-grit conditions

OBJECTIVE

To explore manual wheelchair propulsion strategies for ramp ascent and descent in snow and snow-ice-grit conditions.

DESIGN

Cross-sectional study.

SETTING

Climatic Engineering and Testing Chamber (Ottawa, Canada).

PARTICIPANTS

Manual wheelchair users (N=11) who typically self-propel their wheelchair in winter.

INTERVENTIONS

Ramp ascent and descent at 3 grades (1:10, 1:12, 1:16) and 2 winter conditions (packed snow, packed snow with a freezing rain cover, and traction grit).

MAIN OUTCOMES MEASURES

Type of ascent and descent strategy, success rate, number and severity of obstructions, average speed, and perceived ramp navigation rating. A questionnaire regarding the subject's past experiences with wheelchair propulsion in winter.

RESULTS

Snow accumulation on ramps at 1:10 grade will render the ramp inaccessible for many wheelchair users who do not have external assistance. For snow conditions, the transition area from the level group to the first 2m of ramp incline were the most difficult to traverse for both ascent and descent. All subjects were able to ascend and descend the ramp for the ice-grit condition. Two-railing propulsion is a preferred strategy for ice-grit ramp navigation because of enhanced trajectory control and reducing the potential for wheel-slip problems. Backwards ramp ascent was a successful strategy for ascent in soft-snow conditions.

CONCLUSIONS

The 1:16 grade is preferred for winter ramp navigation. Backwards ramp ascent for snow conditions should be considered for people with sufficient shoulder and trunk range of motion. Two handrails are recommended for exterior ramps for both propulsion and wheelchair extraction from ruts and other snow-related obstacles. For ice ramp navigation, the amount of grit required and the effective time (ie, time to when grit becomes embedded in snow-ice, becoming much less effective) should be addressed in further research. Front wheels typically available with manual wheelchairs are not appropriate for soft-snow conditions.

The influence of altering push force effectiveness on upper extremity demand during wheelchair propulsion

Manual wheelchair propulsion has been linked to a high incidence of overuse injury and pain in the upper extremity, which may be caused by the high load requirements and low mechanical efficiency of the task. Previous studies have suggested that poor mechanical efficiency may be due to a low effective handrim force (i.e. applied force that is not directed tangential to the handrim). As a result, studies attempting to reduce upper extremity demand have used various measures of force effectiveness (e.g., fraction effective force, FEF) as a guide for modifying propulsion technique, developing rehabilitation programs and configuring wheelchairs. However, the relationship between FEF and upper extremity demand is not well understood. The purpose of this study was to use forward dynamics simulations of wheelchair propulsion to determine the influence of FEF on upper extremity demand by quantifying individual muscle stress, work and handrim force contributions at different values of FEF. Simulations maximizing and minimizing FEF resulted in higher average muscle stresses (23% and 112%) and total muscle work (28% and 71%) compared to a nominal FEF simulation. The maximal FEF simulation also shifted muscle use from muscles crossing the elbow to those at the shoulder (e.g., rotator cuff muscles), placing greater demand on shoulder muscles during propulsion. The optimal FEF value appears to represent a balance between increasing push force effectiveness to increase mechanical efficiency and minimize upper extremity demand. Thus, care should be taken in using force effectiveness as a metric to reduce upper extremity demand.

Shoulder demands in manual wheelchair users across a spectrum of activities

OBJECTIVE

Investigate shoulder joint kinetics over a range of daily activity and mobility tasks associated with manual wheelchair propulsion to characterize demands placed on the shoulder during the daily activity of manual wheelchair users.

DESIGN

Case series.

SUBJECTS

Twelve individuals who were experienced manual wheelchair users.

METHODS

Upper extremity kinematics and handrim wheelchair kinetics were measured over level propulsion, ramp propulsion, start and stop over level terrain, and a weight relief maneuver. Shoulder intersegmental forces and moments were calculated from inverse dynamics for all conditions.

RESULTS

Weight relief resulted in significantly higher forces and ramp propulsion resulted in significantly higher moments than the other conditions. Surprisingly, the start condition resulted in large intersegmental moments about the shoulder equivalent with that of the ramp propulsion, while the demand imparted by the stop condition was shown to be equivalent to level propulsion across all forces and moments.

CONCLUSIONS

This study provides characterization of daily living and mobility activities associated with manual wheelchair propulsion not previously reported and identifies activities that result in higher shoulder kinetics when compared to standard level propulsion.

Use of a geared wheelchair wheel to reduce propulsive muscular demand during ramp ascent: analysis of muscle activation and kinematics

BACKGROUND

Shoulder muscle overuse has been linked to the high prevalence of shoulder injuries in manual wheelchair users. Ramp ascent is a barrier that is often faced by manual wheelchair users that requires higher muscle activations than level wheelchair propulsion. Additionally, reported subjective measures of shoulder pain are reduced amongst manual wheelchair users when using a wheelchair wheel outfitted with a gear mechanism. The purpose of the current investigation was to investigate shoulder muscle activation levels and upper limb kinematics during ramp ascent with and without the use of a geared wheel.

METHODS

Thirteen healthy participants (6 male and 7 female) performed ramp ascent on four ramp grades (1:12, 1:10, 1:8, 1:6) using three wheel conditions (gear, no gear, standard). Electromyographic (EMG) activity of select shoulder muscles as well as kinematics of the right upper limb were collected during ramp ascent. Peak and integrated EMG as well as peak wrist, elbow, and shoulder kinematics were obtained from all ramp ascent trials.

FINDINGS

Peak EMG of the shoulder flexors decreased by an average of 17% (P0.0229) during ramp ascent with the geared wheel. Integrated EMG increased by 67% (P0.0034) as a consequence of an 86% increase (P=0.0009) in ramp ascent duration during the geared wheel condition. There were no significant differences between the non-geared and standard wheel conditions.

INTERPRETATION

Caution must be used if using the gear ratio for prolonged periods due to potential for muscle fatigue since the overall muscle effort to move a fixed distance is higher with the gear ratio. Reducing peak demands may benefit wheelchair users with performing more strenuous tasks of daily living.

Comparison of kinematics, kinetics, and EMG throughout wheelchair propulsion in able-bodied and persons with paraplegia: an integrative approach

A systematic integrated data collection and analysis of kinematic, kinetic, and electromyography (EMG) data allow for the comparison of differences in wheelchair propulsion between able-bodied individuals and persons with paraplegia. Kinematic data from a motion analysis system, kinetic data from force-sensing push rims, and electromyography data from four upper-limb muscles were collected for ten push strokes. Results are as follows: Individuals with paraplegia use a greater percentage of their posterior deltoids, biceps, and triceps in relation to maximal voluntary contraction. These persons also reached peak anterior deltoid firing nearly 10 deg earlier on the push rim, while reaching peak posterior deltoid nearly 10 deg later on the push rim. Able-bodied individuals had no triceps activity in the initial stages of propulsion while their paraplegic groups had activity throughout. Able-bodied participants also had, on average, peak resultant, tangential, and radial forces occurring later on the push rim (in degrees). There are two main conclusions that can be drawn from this integrative investigation: (1) A greater "muscle energy," as measured by the area under the curve of the percentage of EMG throughout propulsion, results in a greater resultant joint force in the shoulder and elbow, thus potentially resulting in shoulder pathology. (2) Similarly, a greater muscle energy may result in fatigue and play a factor in the development of shoulder pain and pathology over time; fatigue may compromise an effective propulsive stroke placing undue stresses on the joint capsule. Muscle activity differences may be responsible for the observed kinematic and kinetic differences between the two groups. The high incidence of shoulder pain in manual wheelchair users as compared to the general population may be the result of such differences, although the results from this biomedical investigation should be examined with caution. Future research into joint forces may shed light on this. Further investigation needs to focus on whether the pattern of kinematics, kinetics, and muscle activity during wheelchair propulsion is compensatory or evolutionary by tracking individuals longitudinally.

Redefining the manual wheelchair stroke cycle: identification and impact of nonpropulsive pushrim contact

OBJECTIVES

To create a comprehensive definition of the manual wheelchair stroke cycle, which includes multiple periods of pushrim contact, and to show its improved clinical benefit to wheelchair propulsion analyses.

DESIGN

Cross-sectional biomechanics study.

SETTING

Three motion analysis laboratories.

PARTICIPANTS

Persons (N=54) with paraplegia who use a manual wheelchair.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Pushrim forces, axle moments, and contact angles measured during wheelchair propulsion.

RESULTS

Total force on the pushrim was used to define pushrim contact and positive axle moment was used to identify the included period of propulsive contact. During most strokes, periods of nonpropulsive contact existed before and after propulsive contact. Within these periods, braking moments were applied to the pushrim, resulting in negative power output, or power loss. Including nonpropulsive data decreased mean stroke moment and power. The magnitude and the angle over which braking moments and power loss occurred increased with wheel speed. Mean braking moment and power loss within the initial contact period were significantly (P<.001) related to stroke pattern.

CONCLUSIONS

The proposed definition of the stroke cycle provides a thorough and practical description of wheelchair propulsion. Researchers and clinicians should use this definition to understand and minimize the impact of nonpropulsive contact throughout the stroke.

Wheelchair propulsion demands during outdoor community ambulation

OBJECTIVE

Quantify manual wheelchair propulsion effort during outdoor community ambulation.

DESIGN

Case series.

SUBJECTS

Thirteen individuals (12 with SCI, 1 with spina bifida) who were experienced manual wheelchair users and had no current upper extremity injury or pain complaints.

METHODS

Measurements were obtained from instrumented wheelchair rims during steady-state propulsion as subjects traversed outdoor concrete sidewalk terrain that included smooth level, aggregate level, and a ramp with a smooth surface. Propulsion effort was assessed using the average propulsion moment, average instantaneous power, and work for both upper extremities.

RESULTS

Propulsion effort, captured by the propulsion moment, work and power, varied across ground conditions (p<0.001). Propulsion effort was greater as the rolling resistance increased (i.e., smooth versus aggregate surfaces) and as the inclination angle progressed from level to inclined surfaces. There were no side-to-side differences across ground conditions for the propulsion moment or work. Power generation was significantly greater on the dominant compared to the non-dominant extremity during the more challenging aggregate surface and ramp conditions.

CONCLUSIONS

Propulsion effort varies with demands imposed by different ground conditions. Quantification of wheelchair propulsion demands provides rehabilitations specialists with objective information to guide treatment of patients adapting to manual wheelchair use.

The effect of resultant force at the pushrim on shoulder kinetics during manual wheelchair propulsion: a simulation study

The aim of this study was to determine, by simulation on real data, the effect of modifying the direction or effectiveness of a given force amplitude on the load sustained by the shoulder estimated by joint forces and moments. Kinematics and kinetics data were recorded on 14 manual wheelchair users 68.2+/-5.2 years for 10 s at sub-maximal speed (0.96-1.01 m/s). The simulation consisted in modifying force effectiveness at the pushrim while maintaining the same initial force amplitude. Shoulder kinetics were computed for simulated resultant forces from radial to tangent directions and also for initial force effectiveness. The results show that as the force was simulated tangent to the wheel, there was a significant increase in the average proximal and anterior shoulder joint forces. Also, significant increases in average internal rotation, flexion in the sagittal and horizontal plane moments were reported. Higher shoulder kinetics could accelerate the onset of fatigue and increase the risk of injury. A single-case analysis revealed an improvement window for force effectiveness ( approximately 10%) in which shoulder kinetics were not substantially increased. Our results provide useful information on what would happen to shoulder kinetics if we were able to teach manual wheelchair users to modify their force pattern at the pushrim. The results suggest that for an elderly population, it is not wise to aim at producing a mechanically optimal resultant force at the pushrim (i.e., tangent). Smaller increases of the initial force effectiveness would be preferable.

The effects of arm crank strategy on physiological responses and mechanical efficiency during submaximal exercise

The purpose of this study was to compare submaximal physiological responses and indices of mechanical efficiency between asynchronous and synchronous arm ergometry. Thirteen wheelchair-dependent trained athletes performed eight steady-state incremental bouts of exercise (0 to 140 W), each lasting 4 min, using synchronous and asynchronous arm-cranking strategies. Physiological measures included oxygen uptake (VO2), heart rate, and blood lactate concentration. The power outputs corresponding to fixed whole blood lactate concentrations of 2.0 to 4.0 mmol x l(-1) were calculated using linear interpolation. Mechanical efficiency indices - gross efficiency, net efficiency, and work efficiency - were also calculated. An analysis of variance with repeated measures was applied to determine the effect of crank mode on the physiological parameters. Oxygen uptake was on average 10% lower (P < 0.01), and both net efficiency (P < 0.01) and gross efficiency (P < 0.01) were higher, during the asynchronous strategy at both 60 and 80 W (gross efficiency: 16.9 +/- 2.0% vs. 14.7 +/- 2.4% and 17.5 +/- 1.8% vs. 15.9 +/- 2.6% at 60 and 80 W respectively). There were no differences in heart rate, blood lactate concentration or power output at either of the blood lactate reference points between the asynchronous and synchronous strategies (P > 0.05). In conclusion, test specificity is an important consideration. If a synchronous strategy is to be adopted, it is likely to result in lower efficiency than an asynchronous strategy. The exercise testing scenario may help dictate which method is ultimately chosen.

Stroke pattern and handrim biomechanics for level and uphill wheelchair propulsion at self-selected speeds

OBJECTIVES

To investigate the natural stroke patterns of wheelchair users pushing on a level surface, to determine if users adapt their stroke patterns for pushing uphill, and to assess whether there are biomechanic advantages to one or more of the stroke patterns.

DESIGN

Case series.

SETTING

Biomechanics laboratory.

PARTICIPANTS

Twenty-six manual wheelchair users with a spinal cord injury.

INTERVENTION

Subjects pushed their own wheelchairs at self-selected speeds on a research treadmill set to level, 3 degrees , and 6 degrees grades. Stroke patterns were measured using a motion capture system. Handrim biomechanics were measured using an instrumented wheel.

MAIN OUTCOME MEASURES

Stroke patterns were classified for both level and uphill propulsion according to 1 of 4 common classifications: arcing, semi-circular, single-looping (SLOP), and double-looping (DLOP). Biomechanic outcomes of speed, peak handrim force, cadence, and push angle were all compared across stroke classifications using an analysis of variance.

RESULTS

Only 3 of the 4 stroke patterns were observed. None of the subjects used the semi-circular pattern. For level propulsion, the stroke patterns were fairly balanced between arcing (42%), SLOP (31%), and DLOP (27%). Subjects tended to change their stroke pattern for pushing uphill, with 73% of the subjects choosing the arcing pattern by the 6 degrees grade. No statistically significant differences were found in handrim biomechanics or subject characteristics across stroke pattern groups.

CONCLUSIONS

Wheelchair users likely adapt their stroke pattern to accommodate their propulsion environment. Based on the large percentage of subjects who adopted the arcing pattern for pushing uphill, there may be benefits to the arcing pattern for pushing uphill. In light of this and other recent work, it is recommended that clinicians not instruct users to utilize a single stroke pattern in their everyday propulsion environments.

Engineering better wheelchairs to enhance community participation

With about 2.2 million Americans currently using wheeled mobility devices, wheelchairs are frequently provided to people with impaired mobility to provide accessibility to the community. Individuals with spinal cord injuries, arthritis, balance disorders, and other conditions or diseases are typical users of wheelchairs. However, secondary injuries and wheelchair-related accidents are risks introduced by wheelchairs. Research is underway to advance wheelchair design to prevent or accommodate secondary injuries related to propulsion and transfer biomechanics, while improving safe, functional performance and accessibility to the community. This paper summarizes research and development underway aimed at enhancing safety and optimizing wheelchair design.

Aerobic fitness and upper extremity strength in patients aged 11 to 21 years with spinal cord dysfunction as compared to ideal weight and overweight controls

OBJECTIVE

To determine whether the aerobic fitness, upper extremity strength, and body composition in groups of adolescents with mobility impairment due to thoracic and upper lumbar spinal cord injury (SCI) or spina bifida (SB) are significantly different from those in groups of adolescents without mobility impairment who are of normal weight (CTRL) or overweight (OW).

SUBJECTS

One hundred fifteen total subjects were evaluated including 59 female (19 SB, 9 SCI, 17 OW, and 14 CTRL) and 56 male (18 SB, 10 SCI, 8 OW, and 20 CTRL) participants aged 11 to 21 years.

METHODS

Aerobic fitness was assessed using a ramp protocol with a magnetically braked arm ergometer. Heart rate and oxygen uptake (VO2) were recorded. Peak isokinetic upper arm and shoulder strength values were determined with a dynamometer. Body composition was estimated using dual energy x-ray absorptiometry (DEXA). Male and female subjects were categorized as overweight if their percent body fat by DEXA exceeded 25% and 30%, respectively. Results were analyzed with an ANOVA using the Bonferroni correction. Significance was accepted at P < 0.05.

RESULTS

The percent body fat of both the male and female SB and SCI subjects was significantly higher than CTRL but was not different than OW. In general, the shoulder extension and flexion strength in both the SB and SCI males and females was significantly lower than that of the CTRL and OW. The SCI and SB subjects had significantly reduced aerobic capacity (VO2/kg) compared to the CTRL subjects but were not different than the OW subjects. During the maximal exercise test, the SB and SCI subjects reached exhaustion at significantly lower workloads than the CTRL and OW subjects.

CONCLUSIONS

Patients age 11 to 21 years with SB and SCI had reduced aerobic capacity that was associated with being overweight and having reduced upper extremity strength. These data suggest that interventions to increase strength and fitness and to manage weight should be recommended in this population.

Behavioral intervention, exercise, and nutrition education to improve health and fitness (BENEfit) in adolescents with mobility impairment due to spinal cord dysfunction

BACKGROUND/OBJECTIVE

Determine the effects of a nutrition education and exercise intervention on the health and fitness of adolescents with mobility impairment due to spinal cord dysfunction from myelomeningocele and spinal cord injury. Subjects participated in a 16-week intervention consisting of a behavioral approach to lifestyle change, exercise, and nutrition education to improve fitness (BENEfit) program. Participants were given a schedule of aerobic and strengthening exercises and attended nutrition education and behavior modification sessions every other week along with their parent(s).

SUBJECTS

Twenty adolescents (aged 11-18 years, mean 15.4 +/- 2.2 years) with spinal cord dysfunction.

METHODS

Subjects were tested immediately prior to starting and upon completion of the program. Aerobic fitness was measured using a ramp protocol with an arm ergometer. Heart rate and oxygen uptake were measured. Values at anaerobic threshold and maximum oxygen uptake were recorded. Peak isokinetic arm and shoulder strength were determined with a dynamometer. Body composition was estimated with dual-energy x-ray absorptiometry. Serum chemistry included measures of cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides.

RESULTS

Fourteen individuals completed all testing sessions. There was no significant overall change in weight, body mass index, body mass index z-scores, or serum chemistry. Overall, there was a significant increase in whole body lean tissue without a concomitant increase in whole body fat. Fitness measures revealed a significant increase in maximum power output, work efficiency as measured by the amount of power output produced aerobically, and resting oxygen uptake. Strength measurements revealed a significant increase in shoulder extension strength and a trend towards increased shoulder flexion strength. There were no significant changes in high-density lipoprotein, low-density lipoprotein, total cholesterol, or triglycerides.

CONCLUSIONS

The BENEfit program shows promise as a method for improving the health and fitness of adolescents with mobility impairments who are at high risk for obesity and obesity-related health conditions.

Manual wheelchairs: Research and innovation in rehabilitation, sports, daily life and health

Those with lower limb disabilities are often dependent on manually propelled wheelchairs for their mobility, in Europe today some 3.3 million people. This implies a transfer from leg to arm work for ambulation and all other activities of daily living (ADL). Compared to the legs, arm work is less efficient and more straining, and leads to a lower physical capacity. Also, there is a major risk of mechanical overuse. Problems of long-term wheelchair use are not only pain or discomfort, but also a risk of a physically inactive lifestyle. Subsequently, serious secondary impairments (obesity, diabetes and cardiovascular problems) may eventually emerge. Wheelchair quality, including the ergonomic fitting to the individual may play a preventive role here, but also other modes of physical activity, and the understanding of training, rehabilitation, active lifestyle and sports on health and wellbeing. The 'International Classification of Functioning, Health and Disability' (ICF) model, a stress-strain-work capacity model, as well as the ergonomics model that relates human-activity-assistive technology are instrumental to the concepts, structure and aims of research in assistive technology for mobility. Apart from empirical developments and innovations from within wheelchair sports, systematic research has played a role in wheelchair development and design in three important areas: (1) the vehicle mechanics, (2) the human movement system and (3) the wheelchair-user interface. Current practical developments in design and technology are discussed. A position stand on the key-issues of a current and future research agenda in this area is presented.

The Effect of Visual Biofeedback on the Propulsion Effectiveness of Experienced Wheelchair Users

OBJECTIVE

To determine the effect of visual feedback on the propulsion effectiveness of experienced manual wheelchair users.

DESIGN

Controlled trial.

SETTING

A motion analysis laboratory.

PARTICIPANTS

A convenience sample of 16 healthy men and 2 healthy women with T4-L2 traumatic paraplegia, a mean age of 38+/-9 years, and a mean duration of manual wheelchair-based mobility of 14+/-8 years.

INTERVENTION

Propulsion was assessed as the subjects propelled an instrumented wheelchair (with and without visual biofeedback) on a custom-built dynamometer at propulsion intensities of .15 and .25W/kg for 10 minutes.

MAIN OUTCOME MEASURES

The primary outcome variable was the fraction of effective force (FEF) (ie, the ratio of effective to total force) applied by the subject to the wheelchair's pushrim. Secondary variables included velocity, stroke frequency, and stroke angle.

RESULTS

A 2-factor analysis of variance with repeated measurements was used to detect significant differences between the outcome variables. The FEF ratio was 73.9% without feedback and 72.5% with feedback at the lower-intensity level. Propulsion during the higher intensity condition both with and without feedback resulted in a statistically significant improvement in the FEF (73.9%-78.7% with no feedback, 72.5%-80.2% with feedback), compared with the lower-intensity level. Stroke angle increased from 84.3 degrees to 98.7 degrees and frequency decreased from 66 to 57.8 strokes/min with feedback.

CONCLUSIONS

Visual biofeedback may have little utility in improving the force effectiveness of manual wheelchair propulsion in experienced wheelchair users. Experienced wheelchair users may have already optimized their stroke in a manner that balances energy expenditure with stroke efficiency. Other variables such as stroke length and frequency may be more amenable to visual biofeedback.

Effect of handrim diameter on manual wheelchair propulsion: mechanical energy and power flow analysis

BACKGROUND

Wheelchair design parameters such as handrim diameter could affect propulsion. The purpose of this study was to examine the effect of handrim size (0.54, 0.43, and 0.32 m) on mechanical energy and power flow during wheelchair propulsion.

METHODS

Twelve young normal male adults (mean age 23.5 years old) were recruited in this study. Both 3-D kinematic and kinetic data of the upper extremity were collected synchronously using a Hi-Res Expert Vision motion system and an instrumented wheel during wheelchair propulsion.

FINDINGS

The kinetic, potential and total mechanical energy of the upper extremity increased as the handrim size increased. For each upper arm segment, the joint translational power and the rotational power of the proximal joint increased with increasing handrim size. The work done during a complete propulsion cycle with the larger handrim size is significantly larger than that using a smaller handrim (P<0.05).

INTERPRETATION

The increased kinetic, potential and total mechanical energy were due to the increased linear velocity and the elevated positions of the upper extremity segments. The shoulder and trunk flexors increased the magnitude of their concentric contractions during propulsion with the large handrim as increased output power is required. By using mechanical energy and power flow analysis techniques, we evaluated the previously-reported effect of handrim size on mechanical cost and provided insight into the relationship between the two.