School of Human Movement and Nutrition Sciences, Centre for Sensorimotor Performance, The University of Queensland, St Lucia, Queensland, AUSTRALIA.
Med Sci Sports Exerc. 2020 Dec;52(12):2599-2607. doi: 10.1249/MSS.0000000000002408.
When cyclists ride off the saddle, their center 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 effect on the mechanical power that needs to be generated and dissipated by muscle.
To date, neither the CoM movement strategies during nonseated 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 15 participants riding in a nonseated posture at three individualized power outputs (10%, 30%, and 50% of peak maximal power) and two different cadences (70 and 120 rpm).
The peak-to-peak amplitude of vertical CoM displacement increased 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) occurred under the combination of high-power output and low cadence. 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) was equal to 18% of the peak crank power.
Consequently, 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 the rise and fall of a rider's CoM acts as a mechanical amplifier during nonseated cycling, which has important implications for both rider and bicycle performance.
非坐姿骑行时，骑手的质心（CoM）似乎在每个曲柄周期中经历有节奏的垂直摆动。就像在步行和跑步中一样，CoM 运动模式可能对肌肉需要产生和消耗的机械功率有重大影响。
迄今为止，非坐姿骑行时 CoM 的运动策略以及允许这种现象发生的肢体力学尚未被量化。
在这里，我们通过结合运动学和动力学方法来测量 CoM 运动和 15 名参与者在三个个体化功率输出（10%、30%和 50%的峰值最大功率）和两个不同踏频（70 和 120rpm）下的关节功率，来估计骑手在曲柄周期的每个瞬间 CoM 能贡献多少功率。
垂直 CoM 位移的峰峰值幅度随着功率输出和踏频的降低而显著增加。因此，在高功率输出和低踏频的组合下，CoM 位移的最大峰峰值幅度（0.06±0.01m）和总机械能的变化（0.54±0.12J·kg）最大。在高功率输出和低踏频的相同组合下，我们发现 CoM 能量损失的峰值速率（3.87±0.93W·kg）等于曲柄功率的 18%。
因此，对于给定的功率输出，CoM 能量的变化有助于曲柄的峰值瞬时功率输出，从而减少肌肉的贡献。这些发现表明，在非坐姿骑行时，骑手 CoM 的上升和下降起到了机械放大器的作用，这对骑手和自行车的性能都有重要影响。
