Inverse dynamics and energy analyses of wheelchair locomotion in subjects with spinal cord injury: differences between comfortable and fast speeds

Manual wheelchair users are predisposed to overuse injuries resulting from repetitive movement. This study comprehensively evaluates kinematics, dynamics, and energy during manual wheelchair propulsion at two distinct speeds, utilizing OpenSim. Four participants with paraplegia were instructed to propel a wheelchair at self-selected comfortable and fast velocities. An instrumented wheelchair wheel was used to measure hand reaction forces and propulsion torque. Kinematics was monitored using 18 reflective markers and two clusters, captured by a Motion Analysis system with 12 cameras. Joint angles and torque curves for fast and comfortable conditions were compared employing statistical parametric mapping (SPM). The average speed attained by the subjects for the comfortable and fast velocities were, respectively, 1.26 ± 0.18 m/s and 2.41 ± 0.32 m/s. The fast velocity necessitated a higher propulsive torque (7.91 vs. 26.17 Nm, p < 0.05), tangential (24.25 vs. 84.30 N, p < 0.05), and radial forces (28.62 vs. 63.58 N, p < 0.05) exerted on the wheel. Compared with comfortable, fast velocity propulsion work (7.75 ± 2.58 vs. 27.78 ± 8.76 J, p < 0.005) and the difference of kinetic energy during the propulsion phase (7.06 ± 5.99 vs. 28.15 ± 28.03 J, p < 0.005) were larger. However, a mechanical efficiency index, calculated as the ratio between the kinetic energy increase and the work applied by the user on the wheel, was similar for both velocities.