Physiological response to cycling with both circular and noncircular chainrings

The purpose of this study was to compare physiological variables of endurance-trained cyclists riding with four different chainring designs: round, Shimano Biopace, and two engineered ellipse designs. The ellipse designated Eng10 had the crank arm oriented 10 degrees forward of the major (i.e. longer) axis. Eighty degrees further forward, along the minor axis, was the crank arm orientation for the second ellipse, Eng90. With the major to minor axis ratio of 22.9 cm/16.8 cm (1.36), both ellipses imposed a crank angular velocity variation of 27% relative to the highest velocity assuming constant chain velocity. Best described as a skewed ellipse (i.e., major and minor axes not perpendicular), the Biopace had a major to minor axis ratio of 1.09 thus giving a crank angular velocity variation of 8%. Eleven male cyclists rode at a high (80% of maximum VO2) and a low (60% of maximum VO2) workrate using each chainring. The study was conducted over four consecutive days with the presentation order of the chainrings randomized. Open circuit spirometry was used to collect continuous respiratory data. Heart rate, blood lactate, and cadence values also were measured. None of the physiological variables including rates of oxygen consumption showed significant differences among the chainrings. Thus, the gross efficiency of cycling was not improved by any of the noncircular chainrings. For cycling events where efficiency is a determinant of performance, the noncircular chainrings do not offer any advantage over round chainrings.