Motionscience, Institute of Sport Sciences, Friedrich-Schiller-University Jena, Seidelstrasse 20, 07740 Jena, Germany.
Hum Mov Sci. 2010 Apr;29(2):299-310. doi: 10.1016/j.humov.2010.01.003. Epub 2010 Mar 20.
In locomotion, humans have to deal with irregularities of the ground, i.e., pathways covered with stones, grass, or roots. When they encounter ground with changes in terrain height they seem to use spring-mass dynamics to help passively stabilize their locomotory trajectory. With increasing step heights humans reduce their leg stiffness, but it is as of yet unclear whether these leg adjustments are purely passively achieved or actively in a feed-forward manner. For this, we investigated the stiffness regulation in the ankle and knee joint and analyzed the correlation between EMG, kinematic, and dynamic parameters. Nine healthy participants were running along a 17m runway with a force plate of adjustable height (steps of 0, +5, +10, and +15cm). Whole body kinematics was monitored along with surface electromyography of three selected bilateral lower limb muscles. We found that the stiffness of the ankle joint is adjusted to the vertical height of a step, in a manner similar to global leg stiffness. Furthermore, the integrated 100ms pre-activation of the m. gastrocnemius medialis (GM) depends on the vertical height of a step and correlates highly significantly with the activation of the GM but also with kinematics and dynamics. Consequently, we identified the pre-activation control as a key for altering the leg posture in preparation for altered ground properties (e.g., the height of a step or an obstacle). During the stance phase the control of activation plays a minor role since geometry and the initial conditions (e.g., leg length, landing angle, and landing velocity) ensure an adequate adjustment of joint stiffness as well as leg stiffness.
在运动中，人类必须应对地面的不规则性，即铺满石头、草或树根的路径。当他们遇到地形高度变化的地面时，他们似乎使用弹簧质量动力学来帮助被动地稳定他们的运动轨迹。随着步幅高度的增加，人类会降低腿部的刚度，但目前尚不清楚这些腿部调整是纯粹被动实现的，还是以主动的前馈方式实现的。为此，我们研究了踝关节和膝关节的刚度调节，并分析了肌电图、运动学和动力学参数之间的相关性。九名健康参与者沿着一个 17 米长的跑道跑步，跑道上有一个可调节高度的力板（步高为 0、+5、+10 和+15cm）。同时监测整个身体的运动学和三个选定的双侧下肢肌肉的表面肌电图。我们发现，踝关节的刚度会根据台阶的垂直高度进行调整，其方式类似于整体腿部刚度。此外，内侧腓肠肌（GM）的 100ms 前激活积分取决于台阶的垂直高度，并且与 GM 的激活高度高度相关，但也与运动学和动力学高度相关。因此，我们确定了前激活控制是改变腿部姿势以适应地面特性变化（例如台阶高度或障碍物高度）的关键。在站立阶段，激活的控制作用较小，因为几何形状和初始条件（例如腿部长度、着陆角度和着陆速度）确保了关节刚度和腿部刚度的充分调整。
