Wheelchair propulsion efficiency: movement pattern adaptations to speed changes

Low mechanical efficiency values in wheelchair propulsion are usually explained on the basis of the supply of force and power generated during the push phase. The purpose of this study is to analyze the movement and muscular activity pattern in handrim wheelchair propulsion, focusing on both the push and recovery phases. Data on cardiorespiratory and propulsion technique parameters were obtained from 40 wheelchair basketball players with extensive experience in wheelchair propulsion in six situations: two exercise levels (60% and 80% of individual VO2peak), and three velocities (1.11, 1.67, and 2.22 m.s-1) with constant power output on a treadmill. A two-factor analysis of variance with repeated measurements was applied with "exercise level" and "speed" as the main factors. A significant effect on gross mechanical efficiency was found when the velocity was increased from 1.67 to 2.22 m.s-1. Decreased mechanical efficiency could be explained by a significant change in the acceleration of the wheelchair-user system during recovery, caused by arm and trunk movements, inducing inertial forces to act on the wheelchair. Consequently, mechanical work increased significantly during the recovery phase. These findings indicate that studies on mechanical efficiency in wheelchair propulsion should not only be focussed on power supply during the push phase, but also on the movement pattern during recovery.