Tracking the whole-body centre of mass of humans seated in a wheelchair using motion capture.

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.

Impact of dribbling on spatiotemporal and kinetic parameters in wheelchair basketball athletes.

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.

A high sample rate, wireless instrumented wheel for measuring 3D pushrim kinetics of a racing wheelchair.

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 analysing 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.