Why do appropriate non-circular chainrings yield more crank power compared to conventional circular systems during isokinetic pedaling?

Several studies have been published on the use of eccentric and non-circular chainrings. The findings of these studies have, however, not been consistent. Despite the lack of consistent positive results in terms of physiological responses, a consensus appears to prevail that the improved mechanical effectiveness of the oval chainring may lead to performance enhancement (e.g. increased crank power output) compared to the conventional circular chainwheel. Some authors assume non-circular chainrings may improve pedal dynamics by reducing the effect of the "dead spot" in the pedaling cycle. Other argue that an elliptical chainwheel should more efficiently match the torque output capability of the rider to the torque input requirement of the pedaling cycle. Still other researchers conclude that non-circular chainrings can potentially increase crank power relative to a conventional circular chainring by acting to slowdown the crank angular velocity during the downstroke (power phase) which allows muscles to generate power longer and to produce more external work. The pedal reaction force can be decomposed into a limb-static force and a limbdynamic force (gravity and inertial effects) component. Static forces result from pedal forces only. Dynamic forces and dynamic moments are needed to accelerate/decelerate (to move) the lower limbs. As a consequence crank power, joint-moments and joint-power are the result of static pedal forces and of the dynamic forces/moments. In a theoretical model, by assuming the static pedal forces being zero it becomes possible to investigate the specific impact of the change of the dynamic force component on the bicycle-rider system. Altering the dynamic forces/moments is possible via ovality and shape of the chainring, crank orientation angle, pedaling cadence, anthropometric values and bike geometry. The objective of this study was, relying on a torque-driven bicycle-rider musculoskeletal model