Pedaling cadence effects on mechanical power and muscle contraction timing during cycling

The mechanical energy required to propel the crank may depend on eccentric and concentric muscle actions. However, it is uncertain whether pedaling cadence would elicit changes in concentric and eccentric contributions. Therefore, the purpose of the present study was to investigate the effects of alterations in pedaling cadence on the eccentric and concentric muscle actions. Joint power production and absorption were calculated to assess potential effects from variations in pedaling cadence on joint kinetics. Twenty-one cyclists participated in this study (VO2pico: 64.1 ± 5.0 ml/kg/min; training volume: 368.2 ± 69.5 km/week). In their first session, maximal power output (POMAX) and power output related to the second ventilation threshold (POVT2) were determined during an incremental maximal cycling test to exhaustion. In their second session, cyclists performed two 2-min trials with workload from their POVT2at two different cadences (70 and 90 rpm). Muscle activation of six muscles, pedal forces and lower limb joint kinematics were evaluated. Longer eccentric contraction at 70 rpm for vastus medialis (8%; p &lt; 0.01) and biceps femoris (20%; p = 0.04) were observed compared to 90 rpm. Longer concentric contraction for vastus medialis muscle (10%; p = 0.04) at 90 rpm was observed compared to 70 rpm. There were no differences in joint power production and absorption among pedaling cadences. No alterations in joint power could indicate maintenance of movement when pedaling cadence is changed. Eccentric contractions from knee muscles could be related to joint control, force transmission and reduced energy cost.推动曲柄所需的机械能可能取决于离心（eccentric）与向心（concentric）肌肉收缩。然而，目前尚不清楚骑行踏频是否会对离心与向心肌肉收缩的占比产生影响。因此，本研究旨在探讨骑行踏频变化对离心与向心肌肉收缩的影响。为评估骑行踏频变化对关节动力学的潜在影响，本研究计算了关节的功率产生与吸收情况。本研究共招募21名自行车运动员（峰值摄氧量(VO2peak)：64.1±5.0 ml/kg/min；周训练量：368.2±69.5 km/周）。在首次测试中，受试者通过递增负荷至力竭的骑行测试，测定其最大功率输出（POMAX）以及与第二通气阈值对应的功率输出（POVT2）。在第二次测试中，受试者完成两组2分钟的骑行试验，骑行负荷设定为对应POVT2的强度，踏频分别为70 rpm与90 rpm。研究评估了6块肌肉的肌电激活度、踏板受力以及下肢关节运动学特征。与90 rpm组相比，70 rpm组的股内侧肌（vastus medialis）与股二头肌（biceps femoris）的离心收缩时长分别增加8%（p<0.01）与20%（p=0.04）。而90 rpm组的股内侧肌向心收缩时长较70 rpm组增加10%（p=0.04）。不同骑行踏频下，关节的功率产生与吸收均无显著差异。关节功率未出现明显变化，这提示改变骑行踏频时运动模式得以维持。下肢膝关节周围肌肉的离心收缩可能与关节控制、力传递以及能量消耗降低有关。