This project is about optimizing the planar shape of a 52-tooth chainring for lying in phase handcycling. The angular crank velocity profile of a modeled crank-mechanism was optimized via the complex method algorithm in an inverse dynamics driven musculoskeletal model. The human model was exposed to hand forces caused by a crank torque, ensuring constant work for one revolution. Further, glenohumeral abduction profile was optimized to be certain of proper technique. Mean Cadence was set to 100 rpm.
The optimization revealed an optimized chainring shape resulting in a long duration of the transition phase furthest away from the shoulders and of the pull phase where the angular crank velocity troughs about 3.4 rad•s-1. Opposite, a short duration of the transition phase closest to the shoulders and of the push phase were present, where the angular crank velocity peaks about 16.0 rad•s-1.
However, an experimental crossover study, including 10 inexperienced subjects, showed a significant increase in oxygen uptake by handcycling with the non-circular chainring (1844 ml•min-1 ± 173 SD) compared to a circular chainring (1750 ml•min-1 ± 184 SD), in the last minute out of a 4-min submaximal handcycling bout at constant speed. Further, one elite handcyclist also showed a significant increase in oxygen uptake by cycling with the non-circular chainring (2189 ml•min-1 ± 131 SD) compared to the circular chainring (2006 ml•min-1 ± 179 SD) in the last 2 min out of a 6-min submaximal handcycling bout at constant speed. Therefore, the chainring design failed validation.