Simulation analysis of the influence of the frame stiffness in racing bikes on pedaling movement

Abstract

The frame stiffness in a racing bicycle might influence not only toughness as the frame structure but also performance of an athlete. The purpose of this study is to clarify biodynamic relations between the frame stiffness in a racing bicycle and the physical loads of an athlete by using a forward dynamics simulation model. The human body structure was represented by the 13-rigid-links and 23-degrees-of-freedom model. Based on the theory of multibody dynamics, the frame structure was expressed by combination of 12 rigid pipes, and the frame stiffness was modeled by rotational springs at the connecting joint between the rigid pipes. Spring coefficients were changed according to the thickness of the frame pipes. The pedaling load from the crank was computed by the angular velocity and angular acceleration of the crank. Moreover, the driving force in the bicycle was additionally defined to consider the influence of the frame weight on the human joint load. The human body model was driven by the joint toques to minimize the cost function consisting of the joint loads in the human body and the driving force in the bicycle, and also to keep desired angular velocity of the crank. Validity of the simulation was evaluated by comparing the joint angles and torques with the measured ones. As for the result, the larger stiffness of the frame resulted in smaller the joint loads in the human body, and optimal stiffness would be determined by the balance between the joint loads in the human body and the driving force in the bicycle.

Keywords

• human dynamics
• biomechanics
• sports engineering
• multibody dynamics
• forward dynamics
• optimization
• joint load