Félix Chénier

A new dynamic model of the manual wheelchair for straight and curvilinear propulsion

Due to their mechanical design, current wheelchair ergometers cannot simulate the behaviour of a wheelchair propelled on curvilinear paths. This is because they implement a dynamic model of the Wheelchair-user system propelled on Straight Line only (WSL). In this paper, we present a new dynamic model of the Wheelchair-user propelled on Straight and Curvilinear paths (WSC), along with a characterization method based on measurements recorded on the field. Other than measured geometrical constants and kinetic/kinematic data from instrumented wheels, no information about the dynamic parameters such as the systems mass and its moment of inertia are necessary. The accuracy of the new WSC model was compared with the WSL model. To this end, ten subjects propelled an instrumented wheelchair following straight and curvilinear patterns. The recorded kinetics were fed to both models, and their estimated kinematics were compared to the recorded ones. For the curvilinear patterns, the RMS relative error between the estimated and measured rear wheels velocities over a complete push cycle are lower for the WSC model than for the WSL model. Outward wheel: 7.98% (WSC) vs 12.98% (WSL). Inward wheel: 10.76% (WSC) vs 20.73% (WSL).

A New Brain Imaging Device Based on fNIRS

A new portable brain imaging device based on continuous-wave functional near-infrared spectrometry (fNIRS) is presented. The source-detector part is composed of a multi-wavelength LED and a silicon photodetector that are directly placed on the scalp of the subject. The dimensions of the proposed device are small, as it has to be mounted on the head of an adult person. Acquired data are transmitted in real-time to a laptop for post processing using Matlab. Time- multiplexed light is used to achieve a higher SNR while keeping the device safe for long-term wearing. Preliminary evaluation on adults gave the expected accuracy and compare well with fNIRS characteristics found in literature, that are collected from bulky equipment. With a noise figure of -47 dB and a sampling rate of 23 Hz, the presented device is appropriate to isolate hemodynamic variations, which are strongly related to local cerebral activity.

Proposing a new index to quantify instantaneous symmetry during manual wheelchair propulsion

Propelling a manual wheelchair (MWC) is a strenuous task that causes upper limb musculoskeletal disorders (MSD) in a large proportion of MWC users. Although most studies on MWC propulsion biomechanics assume that MWC propulsion is a relatively symmetric task, recent literature suggests that this is the case only when the assessed outcome measures are averaged over long periods of time, and not over short periods (i.e., instantaneously). No method is currently available to assess instantaneous symmetry. In this work, we present the Instantaneous Symmetry Index (ISI), a new method that quantifies how a variable has been instantaneously asymmetric during a selected time period. Thirteen experienced MWC users propelled on different cross slopes of 0%, 2%, 4%, 6% and 8%. As the cross slope is increased, the upper hand produced less propulsive moments and the lower hand produced more propulsive movements. This has been reflected in the ISI, which increased from 0.20 (0% slope) to 0.84 (8% slope) with a Spearman׳s coefficient of 0.90. The ISI has great potential to evaluate the ability of a user to propel symmetrically and synchronously, and will be a relevant measure to include in future studies on the impact of MWC propulsion asymmetry on MSD risk.

Wheelchair pushrim kinetics measurement: A method to cancel inaccuracies due to pushrim weight and wheel camber

The commercially available SmartWheelTM is largely used in research and increasingly used in clinical practice to measure the forces and moments applied on the wheelchair pushrims by the user. However, in some situations (i.e. cambered wheels or increased pushrim weight), the recorded kinetics may include dynamic offsets that affect the accuracy of the measurements. In this work, an automatic method to identify and cancel these offsets is proposed and tested. First, the method was tested on an experimental bench with different cambers and pushrim weights. Then, the method was generalized to wheelchair propulsion. Nine experienced wheelchair users propelled their own wheelchairs instrumented with two SmartWheels with anti-slip pushrim covers. The dynamic offsets were correctly identified using the propulsion acquisition, without needing a separate baseline acquisition. A kinetic analysis was performed with and without dynamic offset cancellation using the proposed method. The most altered kinetic variables during propulsion were the vertical and total forces, with errors of up to 9N (p<0.001, large effect size of 5). This method is simple to implement, fully automatic and requires no further acquisitions. Therefore, we advise to use it systematically to enhance the accuracy of existing and future kinetic measurements.

Effect of Wheelchair Frame Material on Users’ Mechanical Work and Transmitted Vibration

Wheelchair propulsion exposes the user to a high risk of shoulder injury and to whole-body vibration that exceeds recommendations of ISO 2631-1:1997. Reducing the mechanical work required to travel a given distance (WN-WPM, weight-normalized work-per-meter) can help reduce the risk of shoulder injury, while reducing the vibration transmissibility (VT) of the wheelchair frame can reduce whole-body vibration. New materials such as titanium and carbon are used in todays wheelchairs and are advertised to improve both parameters, but current knowledge on this matter is limited. In this study, WN-WPM and VT were measured simultaneously and compared between six folding wheelchairs (1 titanium, 1 carbon, and 4 aluminium). Ten able-bodied users propelled the six wheelchairs on three ground surfaces. Although no significant difference of WN-WPM was found between wheelchairs (P < 0.1), significant differences of VT were found (P < 0.05). The carbon wheelchair had the lowest VT. Contrarily to current belief, the titanium wheelchair VT was similar to aluminium wheelchairs. A negative correlation between VT and WN-WPM was found, which means that reducing VT may be at the expense of increasing WN-WPM. Based on our results, use of carbon in wheelchair construction seems promising to reduce VT without increasing WN-WPM.

Estimating pushrim temporal and kinetic measures using an instrumented treadmill during wheelchair propulsion: A concurrent validity study

Using ground reaction forces recorded while propelling a manual wheelchair on an instrumented treadmill may represent a valuable alternative to using an instrumented pushrim to calculate temporal and kinetic parameters during propulsion. Sixteen manual wheelchair users propelled their wheelchair equipped with instrumented pushrims (i.e., SMARTWheel) on an instrumented dual-belt treadmill set a 1m/s during a 1-minute period. Spatio-temporal (i.e., duration of the push and recovery phase) and kinetic measures (i.e. propulsive moments) were calculated for 20 consecutive strokes for each participant. Strong associations were confirmed between the treadmill and the instrumented pushrim for the mean duration of the push phase (r=0.98) and of the recovery phase (r=0.99). Good agreement between these two measurement instruments was also confirmed with mean differences of only 0.028s for the push phase and 0.012s for the recovery phase. Strong associations were confirmed between the instrumented wheelchair pushrim and treadmill for mean (r=0.97) and peak (r=0.96) propulsive moments. Good agreement between these two measurement instruments was also confirmed with mean differences of 0.50Nm (mean moment) and 0.71Nm (peak moment). The use of a dual-belt instrumented treadmill represents an alternative to characterizing temporal parameters and propulsive moments during manual wheelchair propulsion.

A Simplified Upper-Body Model to Improve the External Validity of Wheelchair Simulators

During over-ground wheelchair propulsion, upper-body (UB) movement causes intracycle velocity variations that are neglected by current wheelchair simulators. This could affect the external validity of wheelchair propulsion on simulators. In this study, we investigated ways to incorporate these dynamics into the dynamic model(DM) reproduced by wheelchair simulators. We aimed to maximize the DM accuracy and minimize the number of required inputs. First, two DMs were presented: Model RL represented propulsion on a typical roller-based wheelchair simulator and model UB represented over-ground propulsion, modeling the UB as five rigid bodies. Then, three new DMs were presented: Model trunk (TR), model upper arm (UA), and model forearm (FA); these models simplified model UB by estimating the UB kinematics based on the acceleration of only one segment. For all DMs, wheelchair velocity prediction was tested over-ground at a self-selected velocity among 19 experienced manual wheelchair users with a spinal cord injury. UB kinematics was reconstructed based on personalized kinematic patterns recorded on a wheelchair simulator. Models UB and UA were the most accurate: they reduced the root-mean-square intracycle velocity prediction error from 0.044 m/s (RL) to 0.026 m/s (UB) and 0.024 m/s (UA), and reduced the velocity peak time prediction error from -27.7% (RL) to 1.7% (UB) and -7.3% (UA). Implementing model UA instead of model RL on a wheelchair simulator may improve the external validity of wheelchair propulsion on a simulator.