Biomechanical comparison of two racing wheelchair propulsion techniques

Purpose: The purpose was to compare the conventional (CVT) and pars-backhan d (PBT) techniques used for racing wheelchair propulsion. Selected 3-D kine matic characteristics of the upper body and the electromyographic (EMG) sig nals of selected muscles during racing wheelchair propulsion over a roller system were examined. Methods: Eight CVT and seven PBT elite performers ser ved as the subjects. Each subject performed maximum effort pushing for 30 s at a load that simulated overground pushing. Two S-VHS camcorders (60 Hz) were used to obtain 3-D kinematic parameters and muscle activity was monito red using surface electrodes. Results: The CVT was found to have significan t shorter push time. smaller relative push time, and greater relative recov ery time than the PBT. The CVT is a more compact stroke (smaller joint rang e of motion) and the PBT has a faster overall movement speed. Significant d ifferences in arm positions were found between the two techniques at the in stants of hand contact and hand release. and the upper arm was more interna lly rotated at these two instants in the CVT when compared with the PBT. Th e EMG data showed that large variations in muscle activation patterns exist ed in each technique group. In general. the flexor carpi radialis and trice ps brachii were most active in the push phase. The upper trapezius and post ero-middle deltoids were most active in the ascending recovery phase, where as the extensor carpi radialis. biceps brachii, antero-middle deltoids. and pectoralis major were most active during the descending recovery phase. Co nclusions: The greater push time and push angle associated with the PBT sug gest that the PBT may be more suitable for endurance athletes who are less explosive in their pushing strokes. The greater time and angle allow PBT us ers the opportunity to transmit more force to the wheel.