PHYSICAL STRAIN AND MECHANICAL EFFICIENCY IN HUBCRANK AND HANDRIM WHEELCHAIR PROPULSION

The physical strain and mechanical efficiency of manual wheelchair pro pulsion using handrim and hubcrank propelled racing wheelchairs were s tudied during a submaximal wheelchair exercise test on a stationary ro ller ergometer. Ten healthy male able-bodied subjects conducted two ex ercise tests in a random order and measurements of physical strain (ox ygen uptake, minute ventilation, respiratory exchange ratio, heart rat e) and gross mechanical efficiency were obtained. During the experimen t torque data, speed and power output were determined at a sample freq uency of 0.1 Hz. Analysis of variance for repeated measures (p < 0.05) was used to establish differences. The hubcrank propulsion mechanism showed a significantly lower physical strain and higher gross mechanic al efficiency in comparison with the handrim propulsion mechanism. The lower strain and higher efficiency in propelling the hubcrank partly seems to be due to the continuous biphasic cyclic propulsion movement, which allows both push and pull forces to be exerted. This involves f lexor and extensor muscles around elbow and shoulder, leading to a red uced tendency to fatigue in individual muscles in the upper extremity. The more natural and neutral wrist-hand orientation also seems to dim inish finger flexor activity and wrist-stabilizing muscle activity, an d will thus reduce physical strain both with respect to the cardioresp iratory and musculoskeletal systems The latter may influence the tende ncy to develop carpal tunnel problems positively. The reduced strain o f the hubcrank propulsion mechanism clearly has a number of advantages over handrims for the human engine in the short and long run. However , technical innovation should address current practical problems of st eering and braking. Clearly, hubcranks can be used in low-seated wheel chairs (i.e. racing wheelchairs) only, and in subjects with a sufficie ntly large range of motion in the upper extremity. Moreover, the incre ased width is a drawback of hubcranks. Care should be taken while nego tiating doorposts.