Modeling manual wheelchair propulsion cost during straight and curvilinear trajectories

Effects of wheels and tires on high-strength lightweight wheelchair propulsion cost using a robotic wheelchair tester

PURPOSE

This study was designed to investigate the effect of wheel and tire selections on the propulsion characteristics of a high-strength lightweight manual wheelchair using robotic wheelchair propulsion.

MATERIALS AND METHODS

Four configurations were compared with differing combinations of drive wheel tires and casters, with the baseline reflecting the manufacturer configuration of a solid mag drive wheel and 8"×1" caster. The robotic wheelchair tester propelled the chair using pre-generated straight and curvilinear manoeuvres using repeatable and reliable cyclic torque profiles. Additionally, energy loss of the components was measured using coast-down deceleration tests to approximate the system-level rolling resistance of each configuration.

RESULTS

Results indicate a significant decrease in propulsion cost, increased distance travelled and increased manoeuvrability across all configurations, with upgraded casters and tires.

CONCLUSIONS

These results indicated that with better casters and drive wheel tires, the performance of high strength lightweight wheelchairs can be improved and better meet the mobility needs of users.Implications for rehabilitationWheel and tire selection can have a demonstrable impact on the propulsion efficiency of manual wheelchairsCoast-down test protocols can be used as a simple and cost-effective means of assessing representative energy losses across various surfacesWheelchair configurations can be optimized with proper knowledge of the main energetic loss contributions and the environments and contexts of use.

Steering-by-leaning facilitates intuitive movement control and improved efficiency in manual wheelchairs

BACKGROUND

Manual wheelchair propulsion is widely accepted to be biomechanically inefficient, with a high prevalence of shoulder pain and injuries among users. Directional control during wheelchair movement is a major, yet largely overlooked source of energy loss: changing direction or maintaining straightforward motion on tilted surfaces requires unilateral braking. This study evaluates the efficiency of a novel steering-by-leaning mechanism that guides wheelchair turning through upper body leaning.

METHODS

16 full-time wheelchair users and 15 able-bodied novices each completed 12 circuits of an adapted Illinois Agility Test-course that included tilted, straight, slalom, and 180° turning sections in a prototype wheelchair at a self-selected functional speed. Trials were alternated between conventional and steering-by-leaning modes while propulsion forces were recorded via instrumented wheelchair wheels. Time to completion, travelled distance, positive/negative power, and work done, were all calculated to allow comparison of the control modes using repeated measures analysis of variance.

RESULTS

Substantial average energy reductions of 51% (able-bodied group) and 35% (wheelchair user group) to complete the task were observed when using the steering-by-leaning system. Simultaneously, able-bodied subjects were approximately 23% faster whereby completion times did not differ for wheelchair users. Participants in both groups wheeled some 10% further with the novel system. Differences were most pronounced during turning and on tilted surfaces where the steering-by-leaning system removed the need for braking for directional control.

CONCLUSIONS

Backrest-actuated steering systems on manual wheelchairs can make a meaningful contribution towards reducing shoulder usage while contributing to independent living. Optimisation of propulsion techniques could further improve functional outcomes.

Biomechanics of wheelchair turning manoeuvres: novel insights into wheelchair propulsion

Introduction

Wheelchair turning biomechanics is an under researched area despite its obvious relevance to functional mobility of wheelchair users. Wheelchair turns might be linked to a higher risk of upper limb injuries due to the increased forces and torques potentially associated with asymmetric movement. Our aim was to obtain a better theoretical understanding of wheelchair turning by biomechanically analyzing turns compared to steady-state straightforward propulsion (SSSFP).

Methods

Ten able-bodied men received 12-min familiarization and 10 trials (in a random order) of SSSFP and multiple left and right turns around a rectangular course. A Smart^wheel was mounted at the right wheel of a standard wheelchair to measure kinetic parameters during SSSFP and of the inner hand during right turns and the outer hand during left turns. A repeated measures ANOVA was used to detect differences across tasks.

Results

Two strategies were identified: 3% demonstrated roll turns and 97% spin turns. Spin turns consisted of three phases: approach, turning and depart phase. The turning phase was accomplished by increasing peak force (72.9 ± 25.1 N vs. 43.38 ± 15.9 N in SSSFP) of the inner hand, while maintaining high push frequency of the outer hand (1.09 ± 0.20 push/s vs. 0.95 ± 0.13 push/s in SSSFP). Peak negative force and force impulse during the turning phase were much higher than SSSFP, 15.3 ± 15.7 and 4.5 ± 1.7 times higher, respectively.

Conclusion

The spin turn strategy might carry an increased risk of upper limb injuries due to higher braking force and requires particular attention by rehabilitation professionals to preserve upper limb function of long-term wheelchair users.

Effects of Incremental Changes to Frame Mass on Manual Wheelchair Propulsion Cost

The objective of this study was to assess the effects of small, incremental additions to wheelchair frame mass (0 kg, +2 kg, and +4 kg) on the mechanical propulsion characteristics in both straight and curvilinear maneuvers. A robotic propulsion system was used to propel a manual wheelchair over a smooth tiled surface following rectilinear ("Straight") and curvilinear ("Slalom") trajectories. Three unique loading conditions were tested. Propulsion costs and system rolling resistance estimations were empirically collected using the robotic wheelchair tester. Propulsion cost values were equivalent across all loading conditions over the Slalom trajectory. In the Straight trajectory, adding 2 kg on the axle had equivalent propulsion cost to the unloaded configuration. Adding 4 kg on axle was comparable, but not equivalent, to the unloaded configuration with small (≤4.1%) increases in propulsion cost. This study demonstrates that small (0-4 kg) changes to the frame mass have no meaningful impacts on the propulsion characteristics of the manual wheelchair system. Differences in propulsion cost and rolling resistance were detectable but contextually insignificant.

A novel approach to directly measuring wheel and caster rolling resistance accurately predicts user-wheelchair system-level rolling resistance

Introduction

Clinical practice guidelines for preservation of upper extremity recommend minimizing wheelchair propulsion forces. Our ability to make quantitative recommendations about the effects of wheelchair configuration changes is limited by system-level tests to measure rolling resistance (RR). We developed a method that directly measures caster and propulsion wheel RR at a component-level. The study purpose is to assess accuracy and consistency of component-level estimates of system-level RR.

Methods

The RR of N = 144 simulated unique wheelchair-user systems were estimated using our novel component-level method and compared to system-level RR measured by treadmill drag tests, representing combinations of caster types/diameters, rear wheel types/diameters, loads, and front-rear load distributions. Accuracy was assessed by Bland-Altman limits of agreement (LOA) and consistency by intraclass correlation (ICC).

Results

Overall ICC was 0.94, 95% CI [0.91-0.95]. Component-level estimates were systematically lower than system-level (-1.1 N), with LOA +/-1.3 N. RR force differences between methods were constant over the range of test conditions.

Conclusion

Component-level estimates of wheelchair-user system RR are accurate and consistent when compared to a system-level test method, evidenced by small absolute LOA and high ICC. Combined with a prior study on precision, this study helps to establish validity for this RR test method.

Effect of Wheels, Casters and Forks on Vibration Attenuation and Propulsion Cost of Manual Wheelchairs

Manual wheelchair users are exposed to whole-body vibrations as a direct result of using their wheelchair. Wheels, tires, and caster forks have been developed to reduce or attenuate the vibration that transmits through the frame and reaches the user. Five of these components with energy-absorbing characteristics were compared to standard pneumatic drive wheels and casters. This study used a robotic wheelchair propulsion system to repeatedly drive an ultra-lightweight wheelchair over four common indoor and outdoor surfaces: linoleum tile, decorative brick, poured concrete sidewalk, and expanded aluminum grates. Data from the propulsion system and a seat-mounted accelerometer were used to evaluate the energetic efficiency and vibration exposure of each configuration. Equivalence test results identified meaningful differences in both propulsion cost and seat vibration. LoopWheels and SoftWheels both increased propulsion costs by 12-16% over the default configuration without reducing vibration at the seat. Frog Legs suspension caster forks increased vibration exposure by 16-97% across all four surfaces. Softroll casters reduced vibration by 11% over metal grates. Wide pneumatic 'mountain' tires showed no difference from the default configuration. All vibration measurements were within acceptable ranges compared to health guidance standards. Out of the component options, softroll casters show the most promising results for ease of efficiency and effectiveness at reducing vibrations through the wheelchair frame and seat cushion. These results suggest some components with built-in suspension systems are ineffective at reducing vibration exposure beyond standard components, and often introduce mechanical inefficiencies that the user would have to overcome with every propulsion stroke.

Effect of Manual Wheelchair Type on Mobility Performance, Cardiorespiratory Responses, and Perceived Exertion

This study is aimed at comparing the design and configuration of the most commonly used manual wheelchair models through cardiorespiratory responses, perceived exertion, and mobility performance using two different manual wheelchairs, during mobility tasks. A within-group 2 × 3 × 2 controlled experiment was designed with three independent and four dependent variables. The independent variables included wheelchairs, with the levels active wheelchair with a rigid frame and passive wheelchair with foldable frame; conditions with the levels straight line, slalom, and agility; and speed with levels comfortable and fast. Dependent variables included oxygen uptake (VO₂), distance travelled, speed, and perceived exertion. Results show that the active wheelchair yielded more beneficial characteristics although only the effect of wheelchair type on VO₂ efficiency (oxygen uptake per meter travelled) was statistically significant with a large effect size (F(1, 14) = 118.298, p < 0.001, η² = 0.541). The better VO₂ efficiency was achieved with the active wheelchair under all tested conditions. The effect of wheelchair type on Borg scores was also statistically significant, although with a small effect size (F(1, 14) = 10.340, p = 0.006, η² = 0.119); thus, active wheelchair use had lower Borg scores under all trials and was considered less exhausting than the passive wheelchair. In summary, use of the active wheelchair resulted in the users expending less energy per meter travelled and at the same time experiencing less fatigue. This may benefit overall wheelchair mobility and possibly reduce health complications.

Turning in Circles: Understanding Manual Wheelchair Use Towards Developing User-Friendly Steering Systems

For people with physical disabilities, manual wheelchairs are essential enablers of mobility, participation in society, and a healthy lifestyle. Their most general design offers great flexibility and direct feedback, but has been described to be inefficient and demands good coordination of the upper extremities while critically influencing users’ actions. Multiple research groups have used Inertial Measurement Units (IMUs) to quantify physical activities in wheelchairs arguing that knowledge over behavioural patterns in manual wheelchair usage can guide technological development and improved designs. The present study investigates turning behaviour among fulltime wheelchair users, laying the foundation of the development of novel steering systems that allow directing kinetic energy by means other than braking. Three wearable sensors were installed on the wheelchairs of 14 individuals for tracking movement over an entire week. During detected “moving windows”, phases where the velocities of the two rear wheels differed by more than 0.05 m/s were considered as turns. Kinematic characteristics for both turns-on-the-spot as well as for moving turns were then derived from the previously reconstructed wheeled path. For the grand total of 334 km of recorded wheelchair movement, a turn was detected every 3.6 m, which equates to about 900 turns per day on average and shows that changing and adjusting direction is fundamental in wheelchair practice. For moving turns, a median turning radius of 1.09 m and a median turning angle of 39° were found. With a median of 89°, typical turning angles were considerably larger for turns-on-the-spot, which accounted for roughly a quarter of the recognised turns and often started from a standstill. These results suggest that a frequent pattern in daily wheelchair usage is to initiate movement with an orienting turn-on-the-spot, and cover distances with short, straightforward sections while adjusting direction in small and tight moving turns. As large bends often require simultaneous pushing and breaking, this is, perhaps, the result of users intuitively optimising energy efficiency, but more research is needed to understand how the design of the assistive devices implicitly directs users’ movement.

Propulsion Cost Changes of Ultra-Lightweight Manual Wheelchairs After One Year of Simulated Use

Manual wheelchairs are available with folding or rigid frames to meet the preferences and needs of individual users. Folding styles are commonly regarded as more portable and storable, whereas rigid frames are commonly regarded as more efficient for frequently daily use. To date, there are no studies directly comparing the performances of the frame types. Furthermore, while differences have been reported in the longevity of the frame types, no efforts have been made to relate this durability back to the real-world performance of the frames. This study investigated the propulsion efficiencies of four folding and two rigid ultra-lightweight frames equipped with identical drive tires and casters. A robotic wheelchair tester was used to measure the propulsion costs of each chair over two surfaces: concrete and carpet. A motorized carousel was used to drive the chairs 511 km around a circular track to simulate one year of use for each wheelchair. After simulated use, five of the six wheelchairs showed no decrease in propulsion effort, indicating that the frames were able to withstand the stresses of simulated use without a detrimental impact on performance. In the unused "new" condition, rigid chairs were found to have superior (>5%) performance over folding frames on concrete and carpet, and in the "worn" condition rigid chairs had superior performance over folding chairs on concrete but were comparable on the carpeted surface.