| Description |
Most cycling power is produced during leg extension with minimal power production occuring during the transition between the extension-flexion phases. A prolonged leg extension phase and reduced transition phase could increase cycling power by allowing muscles to generate power for a greater portion of the cycle. Noncircular chainrings have been designed to prolong the time spent in the powerful leg extension phase by varying crank angular velocity within the pedal cycle. The purposes of this dissertation were to evaluate the extent to which noncircular chainrings influence power, biomechanics, and metabolic cost during maximal and submaximal cycling. In the first study, I investigated the effects of chainring eccentricity (C = 1.0, R = 1.13, O = 1.24) on maximum cycling power (Pmax) and optimal pedaling rate (RPMopt). Chainring eccentricity did not influence Pmax and RPMopt. Despite reasonable theory regarding a prolonged leg extension phase and reduced transition phase, chainring eccentricity did not influence Pmax and RPMopt during maximal cycling. In the second study, I evaluated the influence of noncircular chainrings on joint-specific kinematics and power production during maximal cycling. Ankle angular velocity was significantly reduced (-13±12% and -37±13% at 90 and 120 rpm, respectively) with the O chainring, whereas knee and hip angular velocities were unaffected during the leg extension phase. Further, joint-specific power production was unaffected by chainring eccentricity. These results demonstrate that redundant degrees of freedom (DOF) in the cycling action (i.e., ankle angle) allowed cyclists to negate the effects of eccentricity and maintain their preferred hip and knee actions. In my third study, I evaluated the extent to which chainring eccentricity influenced metabolic cost and biomechanics of submaximal cycling. My study protocol allowed for separate analysis of eccentricity and pedal speed (known to influence metabolic cost). Chainring eccentricity with similarly matched pedal speeds reduced knee (-10%) and hip (-5%) angular velocities, while metabolic cost and cycling efficiency remained unaffected. Despite small but significant alterations in joint-specific kinematics, chainring eccentricity did not influence metabolic cost or cycling efficiency during submaximal cycling. Taken together, these results indicate that commercially available noncircular chainrings do not provide performance benefits over conventional circular chainrings during maximal and submaximal cycling. |
