Optimum propulsion technique in different wheelchair handrim diameter

Variability in the propulsion technique to manual wheelchair users due to differences in level of injury and wheelchair fit makes detection of subtle changes in technique due to manipulation of individual variables nearly impossible. However, such changes are well suited to analytical modeling techniques, since variables can be manipulated systematically and the effects of the manipulation can be easily quantified. Therefore, we develop a simple two-dimensional model of the upper arm, forearm, and wheelchair wheel to study changes in wheelchair-user interface. Variations in handrim diameter were examined for their influence in the propulsive moment generated by each subject. The larger the handrim, the greater the moment about the wheel axle M_r could attain. The tangential force F_t applied to the handrim was similar among three handrim diameters. However, the radial component of force applied to the handrim increased as handrim diameter decreased. Increasing rim diameter increased the fraction effective force. Both predicted M_r and F_t reached the peak value in the terminal propulsion phase, in agreement with experimental results of the quasi-static wheelchair propulsion, but not dynamic, cyclic wheelchair propulsion. During the middle to terminal propulsion phase, the optimized force vector is not tangential to the handrim and instead, it pass through the upper arm segment which is comparable to dynamic wheelchair propulsion. Optimum analysis could help us to identify the effect of handrim diameter and investigate the related characteristics. Also, through modeling, the mechanical constraints of force application and the inadequate of pushing technique are further understood.