Noncircular Chainrings Do Not Improve Maximum Cycling Power and Joint-Specific Power during Maximal Cycling

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Net cycling power is mainly produced during leg extension and flexion actions with minimal power produced during the transition between extension and flexion. A possible strategy to maximize cycling power is to increase the time spent in extension and flexion, while decreasing the time spent in transition. Noncircular (NC) chainrings can be oriented to prolong the powerful leg extension phase by varying crank angular velocity (ω) within the pedal cycle. However, the degree to which instantaneous crank ω influence muscle and joint actions depends on the degrees of freedom (DOF) in the leg/crank/pedal system. Previous investigations on cycling power using NC chainrings have produced mixed findings. These mixed findings may be due to cyclists exploiting redundant DOF in the leg/crank/pedal system to manipulate joint ω independent of crank ω. PURPOSE: To evaluate the effects of NC chainrings on joint-specific kinematics and power production during maximal cycling. METHODS: Ten healthy trained cyclists (age=34±8yr, mass=72±9kg, height=1.8 ±0.1m) performed maximal cycling trials of 3 s at randomly assigned pedaling rates (60, 90, and 120 rpm), and chainring eccentricities (ratio of major-to-minor axis) of 1.0 (Cir), 1.13 (Rotor), and 1.24 (Osym), respectively. Participants were visually blinded to chainrings. Joint-specific powers were averaged over complete pedal revolutions and extension-flexion phases. Joint-specific kinematics were analyzed for the portion of the pedal cycle where NC chainrings imposed 80% of their eccentricities (ECC80) on crank ω. RESULTS: Joint-specific powers were unaffected by chainring eccentricity. Ankle extension ω was significantly reduced (-13±12% and -37±13% at 90 and 120 rpm, respectively; all p<0.05) with the Osym chainring, whereas knee and hip extension ω were unaffected. Crank ω, ankle, knee, and hip extension ω within ECC80 increased with increasing pedaling rates (all p<0.01). CONCLUSION: NC chainrings did not improve maximum cycling power or alter joint-specific power during maximal cycling. Knee and hip ω remained unaffected with only ankle ω affected by chainring eccentricity. These results suggest that the effects of the NC chainrings on crank ω were eliminated by the cyclists’ ankling action and thus did not alter the major power producing actions of the hip and knee.