Riders use their centre of mass to amplify crank power during non-seated cycling

When cyclists ride off the saddle during climbing and sprinting, their centre of mass (CoM) appears to go through a rhythmic vertical oscillation during each crank cycle. Just like in walking and running, the pattern of CoM movement may have a significant impact on the mechanical power that needs to be generated and dissipated by muscle. To date, neither the CoM movement strategies during non-seated cycling, nor the limb mechanics that allow this phenomenon to occur, have been quantified. Here we estimate how much power can be contributed by a rider’s CoM at each instant during the crank cycle by combining a kinematic and kinetic approach to measure CoM movement and joint powers of fifteen participants riding in a non-seated posture at three individualised power outputs (10%, 30%, and 50% of peak maximal power) and two different cadences (70 rpm and 120 rpm). Our analysis confirmed that vertical oscillations of the CoM occur within each crank cycle, with a peak-to-peak amplitude that increases significantly with power output and with decreasing cadence. Accordingly, the greatest peak-to-peak amplitude of CoM displacement (0.06 ± 0.01 m) and change in total mechanical energy (0.54 ± 0.12 J·kg-1) occurred under the combination of high power output and low cadence. Additionally, at the same combination of high power output and low cadence, we found that the peak rate of CoM energy loss (3.87 ± 0.93 W·kg-1) was equal to 18% of the peak crank power, which coincided with a near horizontal crank position (107 ± 10°). As a consequence, it appears that for a given power output, changes in CoM energy contribute to peak instantaneous power output at the crank, thus reducing the required muscular contribution. These findings suggest that riders can use the inertia of their CoM as a mechanical amplifier during non-seated cycling, which has important implications for both rider and bicycle performance.