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.

Steering-by-leaning: Feasibility of Utilising Dynamic Backrests to Control Steering in Manual Wheelchairs.

OBJECTIVE: Steering-by-leaning is a promising innovation for manual wheelchairs. It may enable improved energy efficiency, one-handed manoeuvrability, and increased trunk activity during wheelchair use in daily life. To explore the feasibility of this concept, the lateral trunk function of active wheelchair users was assessed before comparing 3 preliminary dynamic backrest designs in a virtual steering exercise. DESIGN: Repeated measures, cross-over study. SUBJECTS: A convenience sample of 15 individuals who had been full-time users of manual wheelchair for at least 1 year. METHODS: Active core strength and lateral leaning range of motion were captured while sitting freely. Participants subsequently tested 3 dynamic wheelchair backrest designs on an individually adjusted laboratory wheelchair prototype by performing a virtual steering exercise. Deviations from a target movement path were analysed using repeated measures analysis of variance and Pearson correlation coefficients. RESULTS: Functional leaning range of motion ranged from below 10° to almost 70°, but increased significantly with use of the simplest backrest design based on a 2-dimensional hinge joint. No correlation was found between functional levels and performance parameters in the virtual steering exercise. CONCLUSION: Using an individually fitted and calibrated design, upper body-actuated wheelchair steering using a laterally tilting backrest is accessible to wheelchair users across a wide spectrum of physical abilities.

A 2D lightweight instrumented wheel for assessing wheelchair functionality/activity.

Introduction: Force measurement wheels are essential instruments for analysing manual wheelchair propulsion. Existing solutions are heavy and bulky, influence propulsion biomechanics, and are limited to confined laboratory environments. In this paper, a novel design for a compact and lightweight measurement wheel is presented and statically validated. Methods: Four connectors between the push-rim and wheel-rim doubled as force sensors to allow the calculation of tangential and radial forces as well as the point of force application. For validation, increasing weights were hung on the push-rim at known positions. Resulting values were compared against pre-determined force components. Results: The implemented prototype weighed 2.1 kg and was able to transmit signals to a mobile recording device at 140 Hz. Errors in forces at locations of propulsive pushes were in the range up to ±3.1 N but higher at the frontal extreme. Tangential force components were most accurate. Conclusion: The principle of instrumenting the joints between push-rim and wheel-rim shows promise for assessing wheelchair propulsion in daily life.

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.

Feedback improves compliance of pressure relief activities in wheelchair users with spinal cord injury.

STUDY DESIGN: Prospective cross-sectional pre-post pilot study. OBJECTIVES: This pilot study aimed to evaluate the potential for improving pressure relief behaviour in wheelchair users with spinal cord injury (SCI) using a novel feedback system based on textile pressure sensor technology. SETTING: In- and out-patient clinic of the Spinal Cord Injury Center, Balgrist University Hospital, Zurich, Switzerland. METHODS: Nine wheelchair users with SCI (3 females, 50 ± 12 years of age, 2 tetra- and 7 paraplegics) were equipped with a feedback system (sensomativewheelchair) for three continuous weeks. The system consists of a textile pressure mat and a mobile smartphone application that reminds participants to perform missing pressure reliefs during regular and unobserved wheelchair usage in a customized manner. Pressure reliefs were detected using a subject-specific random forest classifier. Improvements of relief quality, duration and frequency were analysed by comparing week 1 (baseline) with no feedback, i.e., only pressure data recorded, against week 2 (with feedback). Carry-over effects of improved relief behaviour were studied in week 3 (no feedback, pressure data only recorded). RESULTS: All participants increased their relief frequency and performed in median 82% (IQRs: 55%-99%) of the required reliefs while using the feedback system, whereas the median relief frequency was only 11% (IQRs: 10%-31%) during the baseline condition. Every participant who did not perform reliefs of sufficient duration (based on the recommendations of the therapist) during week 1 showed a significant improvement while using the feedback system. CONCLUSION: Subject-specific feedback using the novel feedback system may have the potential for improving the regularity of an individual's relief activities, and may ultimately be an instrument for reducing the risk of developing pressure ulcers.

Low back pain and its relationship with sitting behaviour among sedentary office workers.

The relationships between sedentary lifestyle, sitting behaviour, and low back pain (LBP) remain controversial. In this study, we investigated the relationship between back pain and occupational sitting habits in 64 call-centre employees. A textile pressure mat was used to evaluate and parameterise sitting behaviour over a total of 400 h, while pain questionnaires evaluated acute and chronic LBP. Seventy-five percent of the participants reported some level of either chronic or acute back pain. Individuals with chronic LBP demonstrated a possible trend (t-test not significant) towards more static sitting behaviour compared to their pain-free counterparts. Furthermore, a greater association was found between sitting behaviour and chronic LBP than for acute pain/disability, which is plausibly due to a greater awareness of pain-free sitting positions in individuals with chronic pain compared to those affected by acute pain.

Wheelchair Tilt-in-Space and Recline Functions: Influence on Sitting Interface Pressure and Ischial Blood Flow in an Elderly Population.

Pressure ulcers (PUs) result from localised injury to the skin and underlying tissue and usually occur over a bony prominence as a result of pressure, often in combination with shear forces. Both pressure magnitude and duration are thought to be key risk factors in the occurrence of PUs, thus exposing wheelchair-bound subjects to high risk of PU development. As a result, wheelchairs that incorporate tilt-in-space and recline functions are routinely prescribed to redistribute pressure away from their ischial tuberosities. The goal of this study was to analyse the role of full-body tilt and recline angles in governing sitting interface pressure and blood circulation parameters in elderly subjects and thereby investigate the efficacy of tilt-in-space wheelchairs for aiding pressure relief activity. Sitting interface pressure and ischial blood flow parameters were examined in 20 healthy elderly subjects while seated in a tilt-in-space and recline wheelchair. Five different angles of seat tilt (5°, 15°, 25°, 35°, and 45°) were assessed in combination with three different angles of backrest recline (5°, 15°, and 30°). The results of the study show that when compared to the upright reference posture, every position (except 15°T/5°R) resulted in a significant decrease in sitting interface pressure. Ischial blood flow also showed significant increases at four different positions (45°T/15°R, 15°T/30°R, 35°T/30°R, and 45°T/30°R) but only at larger tilt-in-space and recline angles. The results therefore suggest that small tilt-in-space and recline angles are indeed able to reduce sitting interface pressures, whereas changes in ischial blood flow only occur at larger angles. In the literature, cell deformation is thought to be dominant over tissue ischemia in the development of tissue necrosis and PUs. Therefore, together with our findings it can be concluded that frequently undertaking small adjustments in tilt-in-space and recline angle might be important for preventing cell deformation and any associated cell necrosis. Larger angles of tilt-in-space and recline seem to support blood flow returning to the tissues, which is likely to play a positive role in healing damaged tissue.

Application of Machine Learning Approaches for Classifying Sitting Posture Based on Force and Acceleration Sensors.

Occupational musculoskeletal disorders, particularly chronic low back pain (LBP), are ubiquitous due to prolonged static sitting or nonergonomic sitting positions. Therefore, the aim of this study was to develop an instrumented chair with force and acceleration sensors to determine the accuracy of automatically identifying the user's sitting position by applying five different machine learning methods (Support Vector Machines, Multinomial Regression, Boosting, Neural Networks, and Random Forest). Forty-one subjects were requested to sit four times in seven different prescribed sitting positions (total 1148 samples). Sixteen force sensor values and the backrest angle were used as the explanatory variables (features) for the classification. The different classification methods were compared by means of a Leave-One-Out cross-validation approach. The best performance was achieved using the Random Forest classification algorithm, producing a mean classification accuracy of 90.9% for subjects with which the algorithm was not familiar. The classification accuracy varied between 81% and 98% for the seven different sitting positions. The present study showed the possibility of accurately classifying different sitting positions by means of the introduced instrumented office chair combined with machine learning analyses. The use of such novel approaches for the accurate assessment of chair usage could offer insights into the relationships between sitting position, sitting behaviour, and the occurrence of musculoskeletal disorders.

Occupational sitting behaviour and its relationship with back pain - A pilot study.

Nowadays, working in an office environment is ubiquitous. At the same time, progressively more people suffer from occupational musculoskeletal disorders. Therefore, the aim of this pilot study was to analyse the influence of back pain on sitting behaviour in the office environment. A textile pressure mat (64-sensor-matrix) placed on the seat pan was used to identify the adopted sitting positions of 20 office workers by means of random forest classification. Additionally, two standardised questionnaires (Korff, BPI) were used to assess short and long-term back pain in order to divide the subjects into two groups (with and without back pain). Independent t-test indicated that subjects who registered back pain within the last 24 h showed a clear trend towards a more static sitting behaviour. Therefore, the developed sensor system has successfully been introduced to characterise and compare sitting behaviour of subjects with and without back pain.

Seat pan and backrest pressure distribution while sitting in office chairs.

Nowadays, an increasing amount of time is spent seated, especially in office environments, where sitting comfort and support are increasingly important due to the prevalence of musculoskeletal disorders. The aim of this study was to develop a methodology for chair-specific sensor mat calibration, to evaluate the interconnections between specific pressure parameters and to establish those that are most meaningful and significant in order to differentiate pressure distribution measures between office chairs. The shape of the exponential calibration function was highly influenced by the material properties and geometry of the office chairs, and therefore a chair-specific calibration proved to be essential. High correlations were observed between the eight analysed pressure parameters, whereby the pressure parameters could be reduced to a set of four and three parameters for the seat pan and the backrest respectively. In order to find significant differences between office chairs, gradient parameters should be analysed for the seat pan, whereas for the backrest almost all parameters are suitable.

Are pressure measurements effective in the assessment of office chair comfort/discomfort? A review.

Nowadays, the majority of jobs in the western world involves sitting in an office chair. As a result, a comfortable and supported sitting position is essential for employees. In the literature, various objective methods (e.g. pressure measurements, measurements of posture, EMG etc.) have been used to assess sitting comfort/discomfort, but their validity remains unknown. This review therefore examines the relationship between subjective comfort/discomfort and pressure measurements while sitting in office chairs. The literature search resulted in eight papers that met all our requirements. Four studies identified a relationship between subjective comfort/discomfort and pressure distribution parameters (including correlations of up to r = 0.7 ± 0.13). However, the technique for evaluating subjective comfort/discomfort seems to play an important role on the results achieved, therefore placing their validity into question. The peak pressure on the seat pan, the pressure distribution on the backrest and the pressure pattern changes (seat pan and backrest) all appear to be reliable measures for quantifying comfort or discomfort.

Soft tissue artefacts of the human back: comparison of the sagittal curvature of the spine measured using skin markers and an open upright MRI.

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

Joint angles of the ankle, knee, and hip and loading conditions during split squats.

The aim of this study was to quantify how step length and the front tibia angle influence joint angles and loading conditions during the split squat exercise. Eleven subjects performed split squats with an additional load of 25% body weight applied using a barbell. Each subject's movements were recorded using a motion capture system, and the ground reaction force was measured under each foot. The joint angles and loading conditions were calculated using a cluster-based kinematic approach and inverse dynamics modeling respectively. Increases in the tibia angle resulted in a smaller range of motion (ROM) of the front knee and a larger ROM of the rear knee and hip. The external flexion moment in the front knee/hip and the external extension moment in the rear hip decreased as the tibia angle increased. The flexion moment in the rear knee increased as the tibia angle increased. The load distribution between the legs changed < 25% when split squat execution was varied. Our results describing the changes in joint angles and the resulting differences in the moments of the knee and hip will allow coaches and therapists to adapt the split squat exercise to the individual motion and load demands of athletes.

In vivo spinal posture during upright and reclined sitting in an office chair.

Increasing numbers of people spend the majority of their working lives seated in an office chair. Musculoskeletal disorders, in particular low back pain, resulting from prolonged static sitting are ubiquitous, but regularly changing sitting position throughout the day is thought to reduce back problems. Nearly all currently available office chairs offer the possibility to alter the backrest reclination angles, but the influence of changing seating positions on the spinal column remains unknown. In an attempt to better understand the potential to adjust or correct spine posture using adjustable seating, five healthy subjects were analysed in an upright and reclined sitting position conducted in an open, upright MRI scanner. The shape of the spine, as described using the vertebral bodies' coordinates, wedge angles, and curvature angles, showed high inter-subject variability between the two seating positions. The mean lumbar, thoracic, and cervical curvature angles were 29 ± 15°, -29 ± 4°, and 13 ± 8° for the upright and 33 ± 12°, -31 ± 7°, and 7 ± 7° for the reclined sitting positions. Thus, a wide range of seating adaptation is possible through modification of chair posture, and dynamic seating options may therefore provide a key feature in reducing or even preventing back pain caused by prolonged static sitting.

The spinal curvature of three different sitting positions analysed in an open MRI scanner.

Sitting is the most frequently performed posture of everyday life. Biomechanical interactions with office chairs have therefore a long-term effect on our musculoskeletal system and ultimately on our health and wellbeing. This paper highlights the kinematic effect of office chairs on the spinal column and its single segments. Novel chair concepts with multiple degrees of freedom provide enhanced spinal mobility. The angular changes of the spinal column in the sagittal plane in three different sitting positions (forward inclined, reclined, and upright) for six healthy subjects (aged 23 to 45 years) were determined using an open magnetic resonance imaging (MRI) scanner. An MRI-compatible and commercially available office chair was adapted for use in the scanner. The midpoint coordinates of the vertebral bodies, the wedge angles of the intervertebral discs, and the lumbar lordotic angle were analysed. The mean lordotic angles were 16.0 ± 8.5° (mean ± standard deviation) in a forward inclined position, 24.7 ± 8.3° in an upright position, and 28.7 ± 8.1° in a reclined position. All segments from T10-T11 to L5-S1 were involved in movement during positional changes, whereas the range of motion in the lower lumbar segments was increased in comparison to the upper segments.