Human Movement Biomechanics Research Group, Department of Movement Science, KU Leuven, BELGIUM.
Department of Kinesiology, University of Massachusetts, Amherst, MA.
Med Sci Sports Exerc. 2021 Oct 1;53(10):2111-2118. doi: 10.1249/MSS.0000000000002692.
Runners naturally adopt a stride frequency closely corresponding with the stride frequency that minimizes energy consumption. Although the concept of self-optimization is well recognized, we lack mechanistic insight into the association between stride frequency and energy consumption. Altering stride frequency affects lower extremity joint power; however, these alterations are different between joints, possibly with counteracting effects on the energy consumption during ground contact and swing. Here, we investigated the effects of changing stride frequency from a joint-level perspective.
Seventeen experienced runners performed six running trials at five different stride frequencies (preferred stride frequency (PSF) twice, PSF ± 8%, PSF ± 15%) at 12 km·h-1. During each trial, we measured metabolic energy consumption and muscle activation, and collected kinematic and kinetic data, which allowed us to calculate average positive joint power using inverse dynamics.
With decreasing stride frequency, average positive ankle and knee power during ground contact increased (P < 0.01), whereas average positive hip power during leg swing decreased (P < 0.01). Average soleus muscle activation during ground contact also decreased with increasing stride frequency (P < 0.01). In addition, the relative contribution of positive ankle power to the total positive joint power during ground contact decreased (P = 0.01) with decreasing stride frequency, whereas the relative contribution of the hip during the full stride increased (P < 0.01) with increasing stride frequency.
Our results provide evidence for the hypothesis that the optimal stride frequency represents a trade-off between minimizing the energy consumption during ground contact, associated with higher stride frequencies, without excessively increasing the cost of leg swing or reducing the time available to produce the necessary forces.
跑步者自然会采用与能量消耗最小化对应的步频。虽然自我优化的概念已被广泛认可，但我们缺乏对步频与能量消耗之间关联的机械性理解。改变步频会影响下肢关节的功率；然而，这些改变在关节之间是不同的，可能会对触地和摆动期间的能量消耗产生抵消作用。在这里，我们从关节的角度研究了改变步频的影响。
17 名有经验的跑步者以 12 公里/小时的速度在五个不同的步频（首选步频（PSF）两次、PSF ± 8%、PSF ± 15%）下进行了六次跑步试验。在每次试验中，我们测量代谢能量消耗和肌肉激活，并收集运动学和动力学数据，这些数据使我们能够使用逆动力学计算平均正关节功率。
随着步频的降低，触地时平均正踝关节和膝关节功率增加（P < 0.01），而摆动腿时平均正髋关节功率降低（P < 0.01）。触地时腓肠肌的平均激活也随步频的增加而降低（P < 0.01）。此外，随着步频的降低，触地时正踝关节功率对总正关节功率的相对贡献减少（P = 0.01），而髋部在整个步幅中的相对贡献随步频的增加而增加（P < 0.01）。
我们的结果为以下假设提供了证据：最佳步频代表了在不过度增加腿部摆动成本或减少产生必要力量的时间的情况下，最小化触地期间能量消耗的权衡。
