Dynamic characteristics of a sport wheelchair.

A single subject performed 36 coast-down trials on a hardwood floor in a sport model wheelchair with velocity ranging from 1.28 to 5.31 m/s (4.6 to 19.1 km/h). A portable computer attached to the wheelchair was used to record the time to the nearest 0.001-second of each half-revolution of a rear wheel. The deceleration during each trial was determined with an average coefficient of variation of 2.6 percent from linear regression of velocity versus time values. A significant relationship (r = 0.97) between deceleration and the square of the velocity was noted in an analysis of the values from the 36 trials. Total drag force and power was calculated as a function of wheelchair velocity from this relationship, indicating that the power output needed to propel the wheelchair increased as a function of the velocity cubed. It is speculated that this noted exponential increase in the energy cost of wheelchair propulsion at higher speeds was due mainly to an increase in air drag.