Submaximal Cycling Power Using Noncircular Chainrings

Abstract

During cycling, muscular power is produced during both leg extension and flexion, with minimal power production occurring during the transitions. Prolonged extension and flexion phases and reduced transition phases could increase cycling power by allowing muscles to generate power for a greater portion of the cycle. Noncircular (NC) chainrings could prolong the powerful leg extension phase by varying crank angular velocity (ω) within the pedal cycle. Mixed findings from previous comparisons of circular (C) and NC chainrings may be related to different approaches in quantifying cycling power. One approach common to power meters is to calculate power as the product of average ω and torque (T) for the pedal cycle. This assumption might overestimate power with NC chainrings. PURPOSE: To determine the extent to which the assumption of constant ω overestimates power values during submaximal cycling. METHODS: Eight healthy participants (age=35±8 yr, mass=75±7 kg, height=1.8±0.1 m) performed 5-min steady state cycling on an isokinetic cycle ergometer using a NC chainring. Following a 5-min warm-up, participants cycled at 90% of lactate threshold power (219±51 W) at 80 rpm and repeated the protocol with a C chainring after a 5-min rest. Participants were visually blinded to chainring conditions. Pedal forces were measured with a force sensing pedal and pedal and crank position were measured with optical encoders. T and ω were measured at 240Hz. Power was calculated as: Method 1: P1=[(ΣNn-1 Tn)/N]x[(ΣNn-1 ωn)/N] and Method 2: P2=[ΣNn-1 (Tn x ωn)]/N. A paired t-test was used to compare differences in power calculations between chainring conditions. RESULTS: Calculated power (P1: 110±22 W; P2: 110±22 W) did not differ for C chainring condition. P1 (117±21 W) was 4±1% higher than P2 (112±21 W) for NC chainring condition (p<0.01). CONCLUSIONS: Method 1 overestimated power with a NC chainring as it did not account for the generally sinusoidal ω produced by the NC chainring, where the largest instantaneous T values occurred when instantaneous ω values were below the average. These results suggest that the assumption of constant ω may overestimate power when using NC chainrings and may explain reports of increased cycling power.