Lieberman Daniel E, Warrener Anna G, Wang Justin, Castillo Eric R
Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
J Exp Biol. 2015 Nov;218(Pt 21):3406-14. doi: 10.1242/jeb.125500.
Endurance runners are often advised to use 90 strides min(-1), but how optimal is this stride frequency and why? Endurance runners are also often advised to maintain short strides and avoid landing with the feet too far in front of their hips or knees (colloquially termed 'overstriding'), but how do different kinematic strategies for varying stride length at the same stride frequency affect economy and impact peaks? Linear mixed models were used to analyze repeated measures of stride frequency, the anteroposterior position of the foot at landing, V̇O2 , lower extremity kinematics and vertical ground reaction forces in 14 runners who varied substantially in height and body mass and who were asked to run at 75, 80, 85, 90 and 95 strides min(-1) at 3.0 m s(-1). For every increase of 5 strides min(-1), maximum hip flexor moments in the sagittal plane increased by 5.8% (P<0.0001), and the position of the foot at landing relative to the hip decreased by 5.9% (P=0.003). Higher magnitudes of posteriorly directed braking forces were associated with increases in foot landing position relative to the hip (P=0.0005) but not the knee (P=0.54); increases in foot landing position relative to the knee were associated with higher magnitudes (P<0.0001) and rates of loading (P=0.07) of the vertical ground reaction force impact peak. Finally, the mean metabolically optimal stride frequency was 84.8±3.6 strides min(-1), with 50.4% of the variance explained by the trade-off between minimizing braking forces versus maximum hip flexor moments during swing. The results suggest that runners may benefit from a stride frequency of approximately 85 strides min(-1) and by landing at the end of swing phase with a relatively vertical tibia.
耐力跑者常常被告知要采用每分钟90步的步频，但这种步频的最佳程度如何，原因又是什么呢？耐力跑者还常常被建议保持小步幅，避免双脚在髋部或膝盖前方太远的位置着地（通俗地称为“过度跨步”），但在相同步频下，不同的步幅变化运动学策略如何影响经济性和冲击力峰值呢？采用线性混合模型分析了14名身高和体重差异较大的跑步者的步频、着地时脚的前后位置、摄氧量、下肢运动学以及垂直地面反作用力的重复测量数据，这些跑步者被要求以3.0米/秒的速度分别以每分钟75、80、85、90和95步的步频跑步。步频每增加5步/分钟，矢状面内最大髋屈肌力矩增加5.8%（P<0.0001），着地时脚相对于髋部的位置下降5.9%（P=0.003）。向后的制动力大小增加与脚着地位置相对于髋部的增加相关（P=0.0005），但与膝盖无关（P=0.54）；脚着地位置相对于膝盖的增加与垂直地面反作用力冲击峰值的大小增加（P<0.0001）和加载速率增加（P=0.07）相关。最后，平均代谢最佳步频为84.8±3.6步/分钟，其中50.4%的方差可由在摆动过程中最小化制动力与最大髋屈肌力矩之间的权衡来解释。结果表明，跑步者可能会从大约每分钟85步的步频以及在摆动阶段结束时以相对垂直的胫骨着地中受益。
