Wheelchair cycle crankshaft center height effects on lower limb joint moments for cycling under low workload

Abstract

By attaching a cycle unit to a general-purpose wheelchair, the authors have developed wheelchair cycles that can provide various riding positions. Many reports have described studies of high workloads for athletes examining the relation between a bicycle riding position and kinetics such as joint moments. Nevertheless, few reports describe low workloads in studies targeting people with weak muscles or people with lower limb disability. This study was conducted to elucidate the joint moment for a cycling motion under a low workload with wheelchair cycles having various heights of bottom brackets (BBs), which are defined as the crankshaft center of a cycle. Lower limb trajectory and pedaling force shown by five healthy men were measured when they used wheelchair cycles with BB heights of 260, 500, and 580 mm. Pedaling velocity of 50 rpm was assumed for a 10 W workload. A pedal type force sensor was developed to obtain a change in pedal reaction force during cycling. The joint moment was obtained from the inverse dynamics procedure. For evaluation, to compare waveform characteristics for each BB height, the flexor and extensor moments of the lower limb (hip, knee, ankle) that most contribute to the pedaling exercise were investigated using the average value and amplitude of the joint moment. For lower BB height, low muscle strength is suitable for initial training. For higher BB height, aggressive muscle strength is suitable for training. Particularly for people with weak muscles, a BB height lower than the seat is desirable for rehabilitation.

Keywords

• biomechanics
• bottom bracket
• inverse dynamics
• joint moment
• wheelchair cycle
• people with weak muscles