NON-CIRCULAR CHAIN RING ALLOWS A REDUCTION OF JOINT LOADING IN CYCLING

Abstract

Non-circular (NC) chain rings were primarily designed to improve the mechanical effectiveness of cycling. Their use can be investigated for application in rehabilitation: they could provide a solution to design an effective exercise reducing joint loading. The aim of this study was to analyze the differences in kinematics, energy consumption, and joint moments between circular and NC chain rings, then to identify a profile that can reduce joint loads, maintaining equal mechanical and metabolic works. Five young participants performed two tests on a cycloergometer; one with a circular chain ring and the other with an NC one. The test consisted in 15 min of cycling; during which they were asked to cycle at three different speeds and at two different powers. Stereophotogrammetric and metabolic data were acquired. Statistical analysis was applied on metabolic data. Joint angular velocities were obtained from kinematic data. A two-dimensional (2D) model of cycling was designed to estimate joint moments with both chain rings. A different ring profile was suggested to further reduce joint flexion peak moment. NC chain ring allows a reduction of flexion joint moments with respect to the circular one without significant difference in metabolic and kinematic data. The new profile proposed further decreases maximum knee flexion moment maintaining equal mechanical work.