Department of Anthropology, University at Buffalo, 380 Academic Center, Buffalo, NY 14261, USA
Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA.
J Exp Biol. 2021 Jan 6;224(Pt 1):jeb219667. doi: 10.1242/jeb.219667.
Like other animals, humans use their legs like springs to save energy during running. One potential contributor to leg stiffness in humans is the longitudinal arch (LA) of the foot. Studies of cadaveric feet have demonstrated that the LA can function like a spring, but it is unknown whether humans can adjust LA stiffness in coordination with more proximal joints to help control leg stiffness during running. Here, we used 3D motion capture to record 27 adult participants running on a forceplate-instrumented treadmill, and calculated LA stiffness using beam bending and midfoot kinematics models of the foot. Because changing stride frequency causes humans to adjust overall leg stiffness, we had participants run at their preferred frequency and frequencies 35% above and 20% below preferred frequency to test for similar adjustments in the LA. Regardless of which foot model we used, we found that participants increased LA quasi-stiffness significantly between low and high frequency runs, mirroring changes at the ankle, knee and leg overall. However, among foot models, we found that the model incorporating triceps surae force into bending force on the foot produced unrealistically high LA work estimates, leading us to discourage this modeling approach. Additionally, we found that there was not a consistent correlation between LA height and quasi-stiffness values among the participants, indicating that static LA height measurements are not good predictors of dynamic function. Overall, our findings support the hypothesis that humans dynamically adjust LA stiffness during running in concert with other structures of the leg.
与其他动物一样，人类在跑步时会像弹簧一样利用腿部来节省能量。人类腿部僵硬的一个潜在原因是足部的纵弓（longitudinal arch，LA）。对尸体足部的研究表明，LA 可以像弹簧一样发挥作用，但尚不清楚人类是否可以与更靠近身体的关节协调调整 LA 硬度，以帮助控制跑步时腿部的僵硬程度。在这里，我们使用 3D 运动捕捉技术记录了 27 名成年参与者在测力平板跑步机上跑步的情况，并使用足部的梁弯曲和中足运动学模型计算了 LA 硬度。由于改变步频会导致人类调整整体腿部僵硬程度，我们让参与者以他们的偏好频率以及比偏好频率高 35%和低 20%的频率跑步，以测试 LA 是否有类似的调整。无论我们使用哪种足部模型，我们都发现参与者在低频率和高频率跑步之间显著增加了 LA 的准硬度，这与踝关节、膝关节和整个腿部的变化相吻合。然而，在足部模型中，我们发现将小腿三头肌的力纳入到足部弯曲力中的模型产生了不切实际的高 LA 功估计，因此我们不鼓励这种建模方法。此外，我们发现参与者之间的 LA 高度和准硬度值之间没有一致的相关性，这表明静态 LA 高度测量不能很好地预测动态功能。总的来说，我们的研究结果支持了这样一种假设，即在跑步过程中，人类会与腿部的其他结构一起动态调整 LA 硬度。
