EFFECTIVENESS OF FORCE APPLICATION IN MANUAL WHEELCHAIR PROPULSION INPERSONS WITH SPINAL-CORD INJURIES

The objective of this study was to investigate effectiveness of force application, the ratio power output/energy expenditure, and timing par ameters of wheelchair propulsion in persons with tetraplegia (TP, n = 17) and paraplegia (PP, n = 12), at two different intensity conditions . All subjects performed a maximal exercise test on a wheelchair ergom eter. Exercise bouts with an intensity of 30 to 50% and 60 to 80% of t he maximal power output were analyzed. Effectiveness of force applicat ion, defined as the ratio of the effective force and the total force, was considerably lower in TP, compared with PP Effectiveness of force application in the plane of the wheel was comparable between TP and PP . TP showed a significantly lower effectiveness of force application i n the frontal plane and applied the forces in a more lateromedial dire ction to the hand rim. The ratio power output/energy expenditure, calc ulated as an indication of gross mechanical efficiency, was considerab ly lower in TP and was associated with the effectiveness of force appl ication (r = 0.64; P < 0.01). Timing parameters showed that TP positio ned their hands in a move backward position on the hand rim. Comparing the different intensity conditions revealed that force was applied mo re effectively, and the ratio power output/energy expenditure was high er at the higher intensity condition. Push time, relative to cycle tim e, increased, and beginning angle showed a forward shift with a higher load. TP tended to decrease, whereas PP showed a tendency for an incr ease in stroke angle with a higher load. The low effectiveness and dif ferent pattern of force application in TP should be taken into account when developing other wheelchair propelling mechanisms and training p rograms for this population.