Handrim Forces Research Articles

Effect of power-assistance on upper limb biomechanical and physiological variables during a 6-minute, manual wheelchair propulsion test: a randomised, cross-over study

Purpose Use of a power-assistance wheelchair could reduce the risk of musculoskeletal disorders (MSDs), however, a comprehensive biomechanical evaluation of these systems has not been carried out. This study aimed to evaluate and compare biomechanical UL propulsion variables, and physiological exercise-related variables during the use of a wheelchair with rear drive power assist device (RD-PAD) and a standard manual wheelchair (MW). Materials and methods Twenty-two adults with spinal cord injury were recruited. RD-PAD (SmartDrive system) was fitted to their own MW. An instrumented wheel was used to measure handrim forces, and gas exchange and heart rate were monitored. Participants performed repeated out and back runs for 6 min on a straight outdoor course. Results Distance covered was significantly greater with the RD-PAD (538 ± 104 m versus 470 ± 124 m). Peak mechanical effort during the propulsion phase was significantly lower with the RD-PAD (p < 0.001). Heart rate, metabolic equivalent of task (MET), tidal volume, minute volume, oxygen consumption, and peak oxygen consumption were all significantly lower with the RD-PAD (p < 0.001). Conclusions The results showed that use of RD-PAD increased the distance covered by MW users and reduced the energy costs of propulsion. The biomechanical results indirectly suggest that RD-PAD may reduce the risk of MSD. Implications for Rehabilitation Using the SmartDrive system as propulsion assistance increases the travel autonomy. The SmartDrive system reduces the biomechanical constraints propelling the wheelchair on a slope and low slope. SmartDrive the system reduces the physiological solicitation related to the propulsion of wheelchair.

Assessment of Longitudinal Changes in Manual Wheelchair Handrim Forces and Stroke Patterns in Children with Spinal Cord Injury

<h3>Research Objectives</h3> To identify changes in handrim kinetics and propulsive stroke patterns over time in pediatric manual wheelchair users. <h3>Design</h3> Longitudinal, prospective. <h3>Setting</h3> Motion Analysis Lab at Shriners Hospital for Children- Chicago. <h3>Participants</h3> Six pediatric manual wheelchair users with spinal cord injury. To be eligible, participants were required to be under 21 years of age during their first visit and use a manual wheelchair as their primary mode of mobility. <h3>Interventions</h3> Participants were evaluated in two separate data collection sessions, approximately one year apart. Participants propelled their wheelchair along a 15-meter, tile walkway at a self-selected speed and stroke pattern for multiple trials while kinetic and kinematic data were collected using a Vicon motion capture system and a Smartwheel affixed to their personal wheelchair. <h3>Main Outcome Measures</h3> Handrim peak force, variance of force, and stroke patterns. <h3>Results</h3> Over half of the participants increased their maximum rate of rise (F/t) of resultant force between visits. No trends were observed in the change in average peak resultant force per stroke cycle between visits, though one participant had a large decrease and another had a large increase. The variance of peak resultant force decreased notably in the three oldest participants and decreased in the three youngest participants. The number of types of stroke patterns used for propulsion and the frequency with which each pattern was used changed for all but one participant between visits. <h3>Conclusions</h3> Changes in handrim kinetics and stroke patterns were observed in most participants between visits. This is concerning, as some of these changes, such as decreased variance of peak resultant force and increased maximum rate of rise, have been correlated with shoulder pain and pathology in adults. Additional research using a larger cohort of pediatric manual wheelchair users is indicated to observe changes that could lead to musculoskeletal pain and pathology. <h3>Author(s) Disclosures</h3> None.

BILATERAL INSTRUMENTED WHEEL SYSTEM FOR MEASURING HANDRIM FORCES DURING MANUAL WHEELCHAIR PROPULSION

The purpose of this study was to design and validate a new bilateral instrumented wheel system (IWS) to measure triaxial handrim forces and torques simultaneously during the wheelchair propulsion. The designed and implemented system measures the force applied to the handrims on both sides of a manual wheelchair using 6-axis force/torque sensors. In addition, a user interface receives the measurements from the left and right IWSs. To verify the accuracy of the wheel system, we evaluate force and torque measurements during the static and dynamic tests. The maximum error in static measurements of force and torque are 4.29% and 1.95%, respectively. Likewise, dynamic tests using planar forces and axle torques provide low errors and measurements that are highly correlated with the expected values ([Formula: see text]). The results revealed that the proposed IWS can be used to measure bilateral 3D handrim reaction forces with acceptable accuracy.

Handrim forces during wheelies performance in able-bodied and SCI subjects

Context: Manual wheelchair users must be able to carry out wheelies in order to tackle obstacles in the outdoor environment. To date, no studies have compared balance variables and forces exerted on the handrim during a stationary wheelie between able bodied and spinal cord injury subjects. Objectives: To compare the distribution of forces applied to the handrim and the center of pressure displacement during a stationary wheelie between able-bodied (AB) subjects and manual wheelchair users with spinal cord injury (SCI). Design: Prospective experimental study. Setting: A university hospital laboratory. Participants: 27 participants (14 AB and 13 SCI). Outcome Measure: Each participant performed 3 stationary wheelies of 60 s duration using a wheelchair equipped with an instrumented wheel. Two force platforms were used to calculate the displacement of the center of pressure (DCOP). Results: Median group DCOP amplitude in the anteroposterior axis was smaller and less variable in the AB (19.6 mm [8.1,49.6]) than the SCI (14.9 mm [7.6,141.1]) group. Forces applied to the handrim only differed significantly between the AB (6 N [−13.8,16.6]) and SCI groups (2.7 N [−12.1 21.9]) in the posteroanterior axis. Conclusions: The results showed that the participants with SCI exerted greater PA forces on the handrim, moreover, the direction of force was opposite to that of the AB group, suggesting that the SCI group used a proactive balance strategy while the AB group used a retroactive strategy. The results suggest that the direction of force applied should be considered when teaching individuals to perform wheelies.

Propulsion efficiency in wheelchair tennis: a case study on the influence of the racket on the handrim forces

Abstract Aims: to evaluate how the act of holding a tennis racket influences the application of forces in the handrim during manual wheelchair propulsion at a self-selected comfortable speed and sprint. Methods: A case study was conducted with an experienced wheelchair tennis player who propelled the wheelchair in a straightforward trajectory at two different velocities (self-selected comfortable speed and sprint) in two different conditions (freehand and holding the racket). Kinetic and temporal data of the pushes were obtained with the SmartWheel system attached in substitution to the conventional rear wheel at the dominant side of the player. Results: holding the racket affects the propulsion pattern mainly when an accelerated movement is required (sprint). Compared to the propulsion at a self-selected speed, propelling the chair as fast as possible with the racket in hands resulted in lower total and tangential forces on the handrim, and decreased push time and increased push frequency. Conclusion: Such influence on both kinetic and temporal propulsion impact the mechanical efficiency of the manual wheelchair propulsion, which may, ultimately, affect the sport´s performance. Special attention should be directed to the propulsion training with the racket in maneuvers and motions that are characteristic of the wheelchair tennis match in an attempt to provide the athlete with proper technique for optimal propulsion efficiency and sports performance.

Changes in wheelchair biomechanics within the first 120 minutes of practice: spatiotemporal parameters, handrim forces, motor force, rolling resistance and fore-aft stability

Purpose: During manual wheelchair (MWC) skill acquisition, users adapt their propulsion technique through changes in biomechanical parameters. This evolution is assumed to be driven towards a more efficient behavior. However, when no specific training protocol is provided to users, little is known about how they spontaneously adapt during overground MWC locomotion. For that purpose, we investigated this biomechanical spontaneous adaptation within the initial phase of low-intensity uninstructed training.Materials and methods: Eighteen novice able-bodied subjects were enrolled to perform 120 min of uninstructed practice with a field MWC, distributed over 4 weeks. Subjects were tested during the very first minutes of the program, and after completion of the entire training protocol. Spatiotemporal parameters, handrim forces, motor force, rolling resistance and fore-aft stability were investigated using an instrumented field wheelchair.Results: Participants rapidly increased linear velocity of the MWC, thanks to a higher propulsive force. This was achieved thanks to higher handrim forces, combined with an improved fraction of effective force for startup but not for propulsion. Despite changes in mechanical actions exerted by the user on the MWC, rolling resistance remained constant but the stability index was noticeably altered.Conclusion: Even if no indication is given, novice MWC users rapidly change their propulsion technique and increase their linear speed. Such improvements in MWC mobility are allowed by a mastering of the whole range of stability offered by the MWC, which raises the issue of safety on the MWC.Implications for rehabilitationThe learning process of manual wheelchair locomotion induces adaptations for novice users, who change their propulsion technique to improve their mobility.Several wheelchair biomechanical parameters change during the learning process, especially wheelchair speed, handrim forces, motor force, rolling resistance and fore-aft stability.Fore-aft stability on the wheelchair rapidly reached the tipping limits for users. Technical solutions that preserve stability but do not hinder mobility have to beimplemented, for instance by adding anti-tipping wheels rather than moving the seat forwards with respect to the rear wheels axle.

An instrumented manual wheelchair as a alternative to video analysis for validating locomotion task detection tools

Manual wheelchair (MWC) is a constraining form of locomotion for the musculoskeletal system and many MWC users are concerned by musculoskeletal disorders (MSD). Detecting and quantifying MWC related activities are of high interest for the day-to-day follow-up of patients using a MWC as a primary mode of locomotion. Indeed, it could assist clinician in early identification of MSD occurrence or optimizing the user environment (furnishing arrangements, etc). Since few years, several tools combining sensors and data processing algorithms were developed. However, the validation of these tools is difficult, in particular because video analysis used as a reference is both highly time consuming and sometimes inaccurate due to the cameras field of view. Hence, there is a need of an alternative reference method to facilitate the validation of such tools. As an alternative to video analysis, we propose to use an instrumented MWC, initially dedicated for investigating MWC biomechanics, as a new reference method for tasks identifications. This MWC was equipped with handrim dynamometers to measure handrim forces and two angular potentiometers fixed on rear wheels to determine the MWC trajectory. Data processing included data aggregation followed by multichannel symbolic representation based on force and velocity thresholds. Currently, the method was implemented for flat horizontal displacement and allowed distinguishing resting: start-up, propulsion, braking and turning motion various curvature radii. The method was tested on 18 able-bodied subjects during actual displacements. Results show that for most subjects, the method allowed identifying start-up, propulsion, braking and turning motion tasks. However, a specific adaptation of some thresholds was required for 2 subjects. Since the first subject kept his hands on the handrims during the recovery phase, making difficult the separation of the different tasks and the other subject used a desynchronized propulsion pattern between right and left upper-limbs (close to an alternative push strategy), which resulted in a failure of the identification of propulsion cycle. Even if a real validation of this method against video analysis is still required, the results of the method are encouraging. Some works are still needed to include displacements on more various inclined surfaces and uneven terrain.

Relationship between linear velocity and tangential push force while turning to change the direction of the manual wheelchair.

Wheelchair propulsion is a major cause of upper limb pain and injuries for manual wheelchair users with spinal cord injuries (SCIs). Few studies have investigated wheelchair turning biomechanics on natural ground surfaces. The purpose of this study was to investigate the relationship between tangential push force and linear velocity of the wheelchair during the turning portions of propulsion. Using an instrumented handrim, velocity and push force data were recorded for 25 subjects while they propel their own wheelchairs on a concrete floor along a figure-eight-shaped course at a maximum velocity. The braking force (1.03 N) of the inside wheel while turning was the largest of all other push forces (p<0.05). Larger changes in squared velocity while turning were significantly correlated with higher propulsive and braking forces used at the pre-turning, turning, and post-turning phases (p<0.05). Subjects with less change of velocity while turning needed less braking force to maneuver themselves successfully and safely around the turns. Considering the magnitude and direction of tangential force applied to the wheel, it seems that there are higher risks of injury and instability for upper limb joints when braking the inside wheel to turn. The results provide insight into wheelchair setup and mobility skills training for wheelchair users.

A comparison of static and dynamic optimization muscle force predictions during wheelchair propulsion

The primary purpose of this study was to compare static and dynamic optimization muscle force and work predictions during the push phase of wheelchair propulsion. A secondary purpose was to compare the differences in predicted shoulder and elbow kinetics and kinematics and handrim forces. The forward dynamics simulation minimized differences between simulated and experimental data (obtained from 10 manual wheelchair users) and muscle co-contraction. For direct comparison between models, the shoulder and elbow muscle moment arms and net joint moments from the dynamic optimization were used as inputs into the static optimization routine. RMS errors between model predictions were calculated to quantify model agreement. There was a wide range of individual muscle force agreement that spanned from poor (26.4% Fmax error in the middle deltoid) to good (6.4% Fmax error in the anterior deltoid) in the prime movers of the shoulder. The predicted muscle forces from the static optimization were sufficient to create the appropriate motion and joint moments at the shoulder for the push phase of wheelchair propulsion, but showed deviations in the elbow moment, pronation–supination motion and hand rim forces. These results suggest the static approach does not produce results similar enough to be a replacement for forward dynamics simulations, and care should be taken in choosing the appropriate method for a specific task and set of constraints. Dynamic optimization modeling approaches may be required for motions that are greatly influenced by muscle activation dynamics or that require significant co-contraction.

Hand-Rim Forces and Gross Mechanical Efficiency in Asynchronous and Synchronous Wheelchair Propulsion: A Comparison

To compare the force application characteristics at various push frequencies of asynchronous (ASY) and synchronous (SYN) hand-rim propulsion, 8 able-bodied participants performed a separate sub-maximal exercise test on a wheelchair roller ergometer for each propulsion mode. Each test consisted of a series of 5, 4-min exercise blocks at 1.8 m · s-1 - initially at their freely chosen frequency (FCF), followed by four counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMARTWheel, measuring forces and moments. The gross efficiency (GE) was determined as the ratio of external work done and the total energy expended. The ASY propulsion produced higher force measures for FRES, FTAN, rate of force development & FEF (P<0.05), while there was no difference in GE values (P=0.518). In pair-matched push frequencies (ASY80:SYN60, ASY100:SYN80, ASY120:SYN100 and ASY140:SYN120), ASY propulsion forces remained significantly higher (FRES, FTAN, rate of force development & FEF P<0.05), and there was no significant effect on GE (P=0.456). Both ASY and SYN propulsion demonstrate similar trends: changes in push frequency are accompanied by changes in absolute force even without changes in the gross pattern/trend of force application, FEF or GE. Matched push frequencies continue to produce significant differences in force measures but not GE. This suggests ASY propulsion is the predominant factor in force application differences. The ASY would appear to offer a kinetic disadvantage to SYN propulsion and no physiological advantage under current testing conditions.

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

BackgroundThe 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. MethodsForward 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. FindingsMuscle 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. InterpretationDeviations 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.

Effects of synchronous versus asynchronous mode of propulsion on wheelchair basketball sprinting

Purpose: This study aimed to first investigate synchronous (SYN) versus asynchronous (ASY) mode of propulsion and, second, investigate the wheel camber effects on sprinting performance as well as temporal parameters. Method: Seven wheelchair basketball players performed four maximal eight-second sprints on a wheelchair ergometer. They repeated the test according to two modes of propulsion (SYN and ASY) and two wheel cambers (9° and 15°).Results: The mean maximal velocity and push power output was greater in the synchronous mode compared to the asynchronous mode for both camber angles. However, the fluctuation in the velocity profile is inferior for ASY versus SYN mode for both camber angles. Greater push time/cycle time (Pt/Ct) and arm frequency (AF) for synchronous mode versus asynchronous mode and inversely, lesser Ct and rest time (Rt) values for the synchronous mode, for which greater velocity were observed. Conclusions: SYN mode leads to better performance than ASY mode in terms of maximal propulsion velocity. However, ASY propulsion allows greater continuity of the hand-rim force application, reducing fluctuations in the velocity profile. The camber angle had no effect on ASY and SYN mean maximal velocity and push power output.Implications for RehabilitationThe study of wheelchair propulsion strategies is important for better understanding physiological and biomechanical impacts of wheelchair propulsion for individuals with disabilities.From a kinematical point of view, this study highlights synchronous mode of propulsion to be more efficient, with regards to mean maximal velocity reaching during maximal sprinting exercises.Even if this study focuses on well-trained wheelchair athletes, results from this study could complement the knowledge on the physiological and biomechanical adaptations to wheelchair propulsion and therefore, might be interesting for wheelchair modifications for purposes of rehabilitation.

Hand-rim Forces and Gross Mechanical Efficiency at Various Frequencies of Wheelchair Propulsion

To determine the effects of push frequency changes on force application, fraction of effective force (FEF) and gross efficiency (GE) during hand-rim propulsion. 8 male able-bodied participants performed five 4-min sub-maximal exercise bouts at 1.8 ms(-1); the freely chosen frequency (FCF), followed by 4 counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMART(Wheel), measuring forces and moments. The GE was determined as the ratio of external work done and the total energy expended. Increased push frequency led to reductions in peak resultant force (P<0.05), ranging from 167 to 117 N and peak tangential force (P<0.05), ranging from 117 to 77 N. However, FEF only demonstrated a significant difference between 60% and 140% FCF (69 ± 9% and 63 ± 7, respectively; P<0.05). Work per cycle decreased significantly (P<0.05) and rate of force development increased significantly (P<0.05) with increased push frequency. GE values were significantly lower at 60%, 120% and 140% FCF than 80% and 100% FCF (P<0.05). No meaningful associations were present between FEF and GE. Under the current testing conditions, changes in push frequency are accompanied with changes in the absolute force values, albeit without changes in either the gross pattern/trend of force application or FEF. Changes in GE are not explained by different levels of force effectiveness.

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.

Stroke Pattern and Handrim Biomechanics for Level and Uphill Wheelchair Propulsion at Self-Selected Speeds

Richter WM, Rodriguez R, Woods KR, Axelson PW. 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°, and 6° 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° 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.

Low-impact wheelchair propulsion: Achievable and acceptable

Incidence of upper-limb overuse injuries among the manual wheelchair population has been found to be associated with hand-rim loading characteristics such as impact and peak loading on the hand rim during propulsion. One proposed method to reduce impact and peak loading is the use of a compliant hand rim, one that can displace relative to the wheel when impacted by the hand. A Variable Compliance Hand-Rim Prototype (VCHP) was designed and used to experimentally optimize the level of compliance through subjective and qualitative propulsion outcome measures. Seventeen manual wheelchair users participated in the study. Subjects propelled their wheelchairs using the VCHP set to each of three compliance levels through a maneuverability test course, as well as on a range of grade conditions using a wheelchair treadmill. Biomechanical measures such as peak hand-rim force, rate of loading at impact, and metabolic demand were assessed during treadmill propulsion bouts. No adverse biomechanical side effects to compliance were found. As compliance was increased, user acceptance decreased. All the subjects found the lowest level of compliance (C1) to be acceptable. Use of the C1 hand rim significantly reduced the peak rate of rise in the hand-rim force on the 6% and 8% grades and significantly reduced the average rate of loading for the 2%, 4%, and 6% grades. This study showed that low-impact wheelchair propulsion is both achievable and acceptable to users.

The biomechanics of wheelchair propulsion in individuals with and without upper-limb impairment

We used an instrumented wheelchair ergometer and 3D motion analysis system to collect joint kinematic and temporal data, as well as hand rim and joint kinetics, in 47 manual wheelchair users (MWCUs) (15 with upper-limb impairment and 32 without upper-limb impairment). The group with upper-limb impairment propelled with a higher stroke frequency and reduced hand-rim contact time, and smaller peak joint angles and joint excursion of the wrist, elbow, and shoulder during the contact phase. They also propelled with a reduced power output and reduced hand-rim propulsive and resultant forces, moments, and joint compressive forces. We concluded that these kinematic and kinetic strategies might be a mechanism for allowing MWCUs with upper-limb impairment to remain independent. Additionally, the reduced joint excursion and reduced magnitude of forces may protect them from the development of secondary upper-limb pathologies.

The effect of seat position on manual wheelchair propulsion biomechanics: a quasi-static model-based approach

The position of the seat relative to the rear wheels is generally adjusted to modify the rearward stability of the wheelchair. Recent studies have shown that seat position also has an effect on propulsion biomechanics and suggest that seat position can be optimized. A quasi-static wheelchair propulsion model was developed to investigate the mechanism by which seat position affects propulsion biomechanics. Inputs to the model include the length of the user's arm segments, the position of the user's shoulder, the size of handrim used and the force profile on the handrim. Outputs from the model include joint kinematics, joint torques, push angle, and push frequency. Handrim force profile was determined by averaging the force profile of five wheelchair users. Force profiles were measured using the SMARTWheel. The effect of seat position on push angle was found to be directly affected by the length of the position vector from the hub of the wheel to the shoulder and indirectly affected by the angular orientation of the vector. Decreasing hub to shoulder length was found to increase push angle, decrease push frequency, decrease shoulder torque and increase elbow extension torque. It is suggested that future research investigating the role of seat position on propulsion biomechanics include both the kinematics and kinetics of the upper extremity.

A kinetic analysis of trained wheelchair racers during two speeds of propulsion

The purpose of the study was to investigate the propulsion kinetics of wheelchair racers at racing speeds and to assess how these change with an increase in speed. It was hypothesised that propulsive force would increase in proportion to speed, to accommodate the additional work required. Six wheelchair racers volunteered to participate in this study which required each athlete to push a racing wheelchair at 4.70 and 5.64 m s −1 on a wheelchair ergometer (WERG). Eight pairs (16 in total) of strain gauges, mounted on four bars attached to the hand-rim of a racing wheelchair wheel, measured the medio-lateral and tangential forces applied to the hand-rim. Kinetic data were sampled at 200 Hz while a single on-line (ELITE) infrared camera operating at 100 Hz was positioned perpendicular to the WERG to record the location of the hand with respect to the hand-rim. In general, peak tangential force occurred when the hand was positioned on the hand-rim between 140 and 180°. With the increase in speed, the peak hand-rim forces applied tangentially increased from 132 to 158 N and those applied medio-laterally increased from 90 to 104 N. The ratio of tangential to total measured force was similar at both speeds (80 and 82%, respectively). In conclusion, these data indicate that wheelchair racers adopt a different propulsion strategy than that employed in everyday chairs and that the forces increase in proportion to propulsion speed.

The Relationship between Three-Dimensional Wheelchair Propulsion Techniques and Pushing Economy

Three-dimensional kinematic and physiological data were obtained from 18 wheelchair racers, to allow the relationship between pushing economy and kinematic variables at 4.70 m · s−1 (n = 18) and 6.58 m · s−1 (n = 12) to be examined. Large inter individual differences in wheelchair propulsion styles were present, which made it difficult to identify variables that were associated with pushing economy and indeed to distinguish key variables that were characteristic of an economical wheelchair racer. Furthermore, those variables associated with economy proved inconsistent across the two speeds. However, at both speeds a higher mechanical efficiency and lower push rate were associated with better economy (p &lt; .05). It was also found that the timing parameters were important. In this respect most athletes tended to push through a similar push angle; however, push rate differed between individuals, suggesting that the magnitude and direction of the hand-rim forces may be important for determining economy of propulsion.