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.

Biomechanical Relationships Between Manual Wheelchair Steering and the Position of the Human Body's Center of Gravity

The purpose of this investigation was to analyze the impact of differential steering of a wheelchair with a pushrim on changes in the position of the body's center of gravity. The method assumed measuring the wheelchair trajectory and the body's center of gravity and determining the transverse relocation of the measured body's center of gravity in relation to a point on the wheelchair trajectory. Twenty-seven measurement tests which demonstrated various wheelchair trajectories were carried out within the investigation. The trajectories were 10 to 15 m long and involved moving forward (test 2), reversing (test 3), turning left (test 1) and right (test 4). The factor of deviation of the center of gravity of human body from the wheelchair trajectory was determined for selected characteristic turning maneuvers. The measured values ranged from 51 to 192 mm. The impact of the wheelchair trajectory on the position of the body's center of gravity was demonstrated as a result of this investigation. Consequently, a trajectory deviation factor for relocation of the human body weight on one side of the wheelchair has been demonstrated.

Visuo-locomotor control in persons with spinal cord injury in a manual or power wheelchair for direction change and obstacle circumvention

Many individuals, such as persons with spinal cord injury (SCI), rely on wheeled locomotion involving manual (MWC) or power (PWC) wheelchairs to navigate their environments. Yet, visuo-locomotor control underlying WC navigation in experienced users is not well understood. The objective of this study was to compare the visuo-locomotor control between MWC and PWC in individuals with SCI while changing direction and circumventing an obstacle. Participants with SCI using a MWC (n = 12, 38.5 ± 10.7 years) or a PWC (n = 10, 47.8 ± 8.6 years) were asked to maneuver their chair straight ahead, while changing direction 45° to the right, and while circumventing an obstacle to the right, all at self-selected speeds. Speed, minimal clearance, point of deviation, temporal body and WC coordination, relative timing of segment rotations and visual behavior were analyzed. There was no main effect of group for speed, clearance and point of deviation. During direction change, the head always led body and wheelchair reorientation while an "en bloc" strategy was used for circumventing obstacle for both groups. In straight-ahead locomotion, participants predominantly fixed their gaze on the end target. During direction change and obstacle circumvention, participants fixated more on the future path and the obstacle for both WC modes. Overall, specific gaze behavior depended on environmental demands. While MWC and PWC users adopt similar navigational strategies and visuo-locomotor coordination while changing direction and circumventing obstacle, there were some differences in the amount of head rotation that could be related to a counter-movement used more by PWC users.