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Estimating the position of the whole-body centre of mass (CoM) based on skin markers and anthropometric tables requires tracking the pelvis and lower body, which is impossible for wheelchair users due to occlusion. In this work, we present a method to track the user's whole-body CoM using visible markers affixed to the user and wheelchair where the user remains seated in their wheelchair, by expressing the pelvis and lower body segments in wheelchair coordinates. The accuracy of this method was evaluated on the anterior-posterior (AP) and medial-lateral (ML) axes by comparing the projected CoM to the centre of pressure measured by four force plates, for 11 able-bodied participants adopting 9 static postures that include extreme reaching postures. The estimation accuracy was within 33 mm (AP) and 9 mm (ML), with a precision within 23 mm (AP) and 12 mm (ML). Tracking the whole-body CoM during wheelchair propulsion will allow researchers to better understand the dynamics of propulsion, which may help devise new approaches to increase the energy transfer from the arms to the ground and reduce the risks of developing musculoskeletal disorders., Comment: 13 pages, 5 figures, 1 table

In wheelchair racing, measuring pushrim kinetics such as propulsion forces and moments is paramount for improving performance and preventing injuries. However, there is currently no instrumented racing wheel that records 3D pushrim kinetics wirelessly and at a high sample rate, which is necessary for accurately analyzing wheelchair racing biomechanics. In this work, we present an instrumented wheel that measures 3D kinetics at 2500 Hz. Bidirectional wireless communication is used to interface the wheel through a smart phone. The wheel was tested with a world-class racing athlete who propelled at maximal acceleration and maximal speed on a training roller. During acceleration, the peak total force increased continuously from 186 N to 484 N while the peak tangential force was constant at 171 N ± 15 N. At higher speeds, a counterproductive tangential force was measured during the first 15 and the last 25 of the push phase, peaking at -78 N. This wheel may be of great value for both coaches and athletes to help with planning and validating training programs and adaptations to the wheelchair such as positioning. This wheel also has very high potential for further research on wheelchair racing biomechanics and on preventing shoulder pathologies associated with this sport.

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.

The use of the ground reaction forces recorded while propelling a manual wheelchair on an instrumented treadmill may represent a valuable alternative to the use of instrumented pushrim to compute 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 1 m/s during a 1-minute period. Spatiotemporal (i.e., push and recovery phase durations) and kinetic measures (i.e. propulsive moments) were computed for 20 consecutive strokes for each participant. Strong associations were confirmed between 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). A good agreement between these two measurement instrument was also confirmed with mean differences of only 0.028s (push phase) and 0.012s (recovery phase). Strong associations were confirmed between the instrumented wheelchair pushrim and treadmill for the mean (r=0.97) and peak propulsive moments (r=0.96). A good agreement between these two measurement instruments was also confirmed with mean differences of 0.50 N.m (mean moment) and 0.71 N.m (peak moment). The use of a dual-belt instrumented treadmill represents an alternative to characterize temporal parameters and propulsive moment during manual wheelchair propulsion.

During overground wheelchair propulsion, upper body movement causes intra-cycle velocity variations that are neglected by current wheelchair simulators. This could affect the external validity of wheelchair propulsion on simulators. In this work, 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 (upper body) represented overground propulsion, modelling the upper body as 5 rigid bodies. Then, three new DMs were presented: Model TR (trunk), model UA (upper arm) and model FA (forearm); these models simplified model UB by estimating the upper body kinematics based on the acceleration of only one segment. For all DMs, wheelchair velocity prediction was tested overground at a self-selected velocity among 19 experienced manual wheelchair users with a spinal cord injury. Upper body 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 intra-cycle 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.

Estimating the position of the whole-body centre of mass (CoM) based on skin markers and anthropometric tables requires tracking the pelvis and lower body, which is impossible for wheelchair users due to occlusion. In this work, we present a method to track the user’s whole-body CoM using visible markers affixed to the user and wheelchair where the user remains seated in their wheelchair, by expressing the pelvis and lower body segments in wheelchair coordinates. The accuracy of this method was evaluated on the anterior-posterior (AP) and medial–lateral (ML) axes by comparing the projected CoM to the centre of pressure measured by four force plates, for 11 able-bodied participants adopting 9 static postures that include extreme reaching postures. The estimation accuracy was within 33 mm (AP) and 9 mm (ML), with a precision within 23 mm (AP) and 12 mm (ML). Tracking the whole-body CoM during wheelchair propulsion will allow researchers to better understand the dynamics of propulsion, which may help devise new approaches to increase the energy transfer from the arms to the ground and reduce the risks of developing musculoskeletal disorders.

Background: Wheelchair basketball is one of the most popular Paralympic sports. Dribbling a ball while propelling is a key feature of wheelchair basketball. Very few studies have investigated the biomechanical impact of dribbling. This study aims to analyze the impact of dribbling on the amplitude and symmetry of spatiotemporal and kinetic parameters of wheelchair propulsion. Methods: Ten experienced wheelchair basketball athletes (31.5 ± 10.6 years old; 7 men, 3 women) with various classifications performed eight 9-m sprints along a straight line on a basketball court: four sprints using classic synchronous propulsion, and four sprints while dribbling a ball down the court. Findings: Dribbling decreased velocity, mean propulsive moments and the force rate of rise, as well as increased push time, force rate of rise asymmetry and angular impulse asymmetry. All kinetic variables were asymmetric and higher on the dominant limb. Interpretation: The combination of reduced velocity and propulsive moments when dribbling indicates that wheelchair basketball athletes may deliberately preserve a safety margin of acceleration to adapt to uncontrolled ball rebounds. Dribbling was not associated with any factors associated with an increased risk of musculoskeletal disorders.

Background: Kinematics is studied by practitioners and researchers in different fields of practice. It is therefore critically important to adhere to a taxonomy that explicitly describes positions and movements. However, current representation methods such as cardan and Euler angles fail to report shoulder angles in a way that is easily and correctly interpreted by practitioners, and that is free from numerical instability such as gimbal lock. Methods: In this paper, we comprehensively describe the recent Tilt-and-Torsion method and compare it to the Euler YXY method currently recommended by the International Society of Biomechanics. While using the same three rotations (plane of elevation, elevation, humeral rotation), the Tilt-and-Torsion method reports humeral rotation independently from the plane of elevation. We assess how it can be used to describe shoulder angles (1) in a simulated assessment of humeral rotation with the arm at the side, which constitutes a gimbal lock position, and (2) during an experimental functional task, with 10 wheelchair basketball athletes who sprint in straight line using a sports wheelchair. Findings: In the simulated gimbal lock experiment, the Tilt-and-Torsion method provided both humeral elevation and rotation measurements, contrary to the Euler YXY method. During the wheelchair sprints, humeral rotation ranged from 14 deg (externally) to 13 deg (internally), which is consistent with typical maximal ranges of humeral rotation, compared to 65 deg to 50 deg with the Euler YXY method. Interpretation: Based on our results, we recommend that shoulder angles be expressed using Tilt-and-Torsion angles instead of Euler YXY.

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.

The use of the ground reaction forces recorded while propelling a manual wheelchair on an instrumented treadmill may represent a valuable alternative to the use of instrumented pushrim to compute 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 1 m/s during a 1-minute period. Spatiotemporal (i.e., push and recovery phase durations) and kinetic measures (i.e. propulsive moments) were computed for 20 consecutive strokes for each participant. Strong associations were confirmed between 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). A good agreement between these two measurement instrument was also confirmed with mean differences of only 0.028s (push phase) and 0.012s (recovery phase). Strong associations were confirmed between the instrumented wheelchair pushrim and treadmill for the mean (r=0.97) and peak propulsive moments (r=0.96). A good agreement between these two measurement instruments was also confirmed with mean differences of 0.50 N.m (mean moment) and 0.71 N.m (peak moment). The use of a dual-belt instrumented treadmill represents an alternative to characterize temporal parameters and propulsive moment during manual wheelchair propulsion.

During overground wheelchair propulsion, upper body movement causes intra-cycle velocity variations that are neglected by current wheelchair simulators. This could affect the external validity of wheelchair propulsion on simulators. In this work, 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 (upper body) represented overground propulsion, modelling the upper body as 5 rigid bodies. Then, three new DMs were presented: Model TR (trunk), model UA (upper arm) and model FA (forearm); these models simplified model UB by estimating the upper body kinematics based on the acceleration of only one segment. For all DMs, wheelchair velocity prediction was tested overground at a self-selected velocity among 19 experienced manual wheelchair users with a spinal cord injury. Upper body 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 intra-cycle 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.

In wheelchair racing, measuring pushrim kinetics such as propulsion forces and moments is paramount for improving performance and preventing injuries. However, there is currently no instrumented racing wheel that records 3D pushrim kinetics wirelessly and at a high sample rate, which is necessary for accurately analyzing wheelchair racing biomechanics. In this work, we present an instrumented wheel that measures 3D kinetics at 2500 Hz. Bidirectional wireless communication is used to interface the wheel through a smart phone. The wheel was tested with a world-class racing athlete who propelled at maximal acceleration and maximal speed on a training roller. During acceleration, the peak total force increased continuously from 186 N to 484 N while the peak tangential force was constant at 171 N ± 15 N. At higher speeds, a counterproductive tangential force was measured during the first 15 and the last 25 of the push phase, peaking at -78 N. This wheel may be of great value for both coaches and athletes to help with planning and validating training programs and adaptations to the wheelchair such as positioning. This wheel also has very high potential for further research on wheelchair racing biomechanics and on preventing shoulder pathologies associated with this sport.