Duty Cycle Alters Maximal Cycling Power

Abstract

1145 We recently reported that increasing the portion of a pedaling cycle occupied by the leg extension phase from 50% to 58% (duty cycle) significantly increased maximal power by 4%. Similarly, Askew and Marsh (1997) reported that increasing the portion an in vitro work loop occupied by the muscle shortening phase from 50% to 75% increased muscular power by 40%. Our previous choice to use a 58% duty cycle was limited by methodological constraints but we have since developed techniques that allow us to evaluate greater duty cycles. Purpose: To test the hypothesis that increases in duty cycle beyond 58% would produce greater increases in maximal cycling power. Methods: Following three days of practice, male cyclists performed maximal cycle ergometry at pedaling rates ranging from 60 to 170 revolutions per minute against an inertial load with duty cycles of 50, 58, 65 or 70%. Duty cycle was altered by positioning the crank sprocket off-center with respect to the crank axle. Pedal forces were recorded via force transducers mounted on the right pedal, and pedal and crank position were recorded via digital position sensors. Data were sampled for 6 seconds at 200Hz. Pedal force and crank angular velocity were used to calculate power produced by the right leg. Power was averaged over each complete cycle, and over the extension phase and flexion phase of each cycle. Results: Maximum power, averaged over a complete cycle was 581 ± 67, 616 ± 67, 602 ± 47, and 564 ± 104 watts for the 50, 58, 65, and 70% duty cycles, respectively. Average leg extension power was 1030 ± 46, 1207 ± 32, 1411 ± 22, and 1486 ± 23 watts (normalized to a complete cycle), whereas average leg flexion power was 38 ± 46, −77 ± 98, −263 ± 58, −371 ± 31watts for duty cycles of 50, 58, 65, and 70% respectively. Conclusion: These data did not fully support our hypothesis. Although leg extension power increased significantly with each increase in duty cycle, average power was compromised at the larger duty cycles due to reduced flexion power. These results highlight the complex nature of maximal cycling in which power is produced throughout the pedaling cycle by both legs.