A theoretical basis for interpreting the force applied to the pedal in cycling

This article presents an analytical technique for decomposing the pedal force in cycling into a muscular component due directly to the net intersegmental moments and a nonmuscular component due to gravitational and inertial effects. The decomposition technique uses the Newton-Euler system of dynamic equations for the leg segments to solve for the two components, given the planar segmental kinematics and the intersegmental moments. Applications of the technique to cycling studies of muscle function, pedalling effectiveness, and optimization analyses based on inverse dynamics are discussed. While this article focuses on the pedal force in cycling, the decomposition method can be directly applied to analyze the reaction forces during a general planar movement of the leg when the segmental kinematics and intersegmental moments are specified. This article also demonstrates the significance of the nonmuscular component relative to the muscular component by performing the decomposition of the pedal forces of an example subject who pedalled at three different cadences against a common work load. The key results were that the nonmuscular components increased in magnitude as the cadence increased, whereas the magnitude of the muscular component remained relatively constant over the majority of the crank cycle. Also, even at the slowest pedalling rate of 70 rpm, the magnitude of the nonmuscular component was substantial.