Validity of power output estimation for wheelchair locomotion

The purpose of this study was to validate an in-field method of estimating power output (PO) requirements for manual wheelchair (WC) locomotion. PO was calculated from the average force required to push a WC and its occupant over level tile and low pile carpeted surfaces multiplied by the locomotive velocity (3 km.hr-1). Average pushing force was determined by a strain-gauge transducer and an electronic integrator. Ten male volunteers (wt in WC = 73 -96 kg) were found to require PO levels ranging from 38 to 63 kpm.h4-1 and 98 to 135 kpm.min-1 for WC locomotion on the tiled and carpeted surface, respectively. Subjects then propelled the WC over the test surfaces at 3 km.h4-1 while steady state VO2, VE and HR were monitored. These variables were also monitored while the subjects operated a wheelchair ergometer (WERG) at corresponding PO levels. VO2 and VE were found to be about 15% higher, and HR about 3% higher for actual WC locomotion. High correlations were found for these variables between WC and WERG operation. Somewhat higher response values for WC locomotion may in part be due to the additional load of steering, inertial forces and weight of the gas collection apparatus. The similarity of these responses for both modes of exercise, however, suggests the validity of this method of determining PO requirements for WC locomotion.