Objective: To examine the impact of surface type, wheelchair weight, and rear axle position on older adult propulsion biomechanics.
Design: Crossover trial.
Setting: Biomechanics laboratory.
Participants: Convenience sample of 53 ambulatory older adults with minimal wheelchair experience (65-87y); men, n=20; women, n=33.
Intervention: Participants propelled 4 different wheelchair configurations over 4 surfaces: tile, low carpet, high carpet, and an 8% grade ramp (surface, chair order randomized). Chair configurations included (1) unweighted chair with an anterior axle position, (2) 9.05 kg weighted chair with an anterior axle position, (3) unweighted chair with a posterior axle position (Delta0.08 m), and (4) 9.05 kg weighted chair with a posterior axle position (Delta0.08 m). Weight was added to a titanium folding chair, simulating the weight difference between very light and depot wheelchairs. Instrumented wheels measured propulsion kinetics.
Main outcome measures: Average self-selected velocity, push frequency, stroke length, peak resultant and tangential force.
Results: Velocity decreased as surface rolling resistance or chair weight increased. Peak resultant and tangential forces increased as chair weight increased, as surface resistance increased, and with a posterior axle position. The effect of a posterior axle position was greater on high carpet and the ramp. The effect of weight was constant, but was more easily observed on high carpet and ramp. The effects of axle position and weight were independent of one another.
Conclusion: Increased surface resistance decreases self-selected velocity and increases peak forces. Increased weight decreases self-selected velocity and increases forces. Anterior axle positions decrease forces, more so on high carpet. The effects of weight and axle position are independent. The greatest reductions in peak forces occur in lighter chairs with anterior axle positions.