Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Department of Neurology, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Sport and Exercise Science Research Centre, School of Applied Sciences, London South Bank University, London, United Kingdom.
Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Department of Neurology, Bayreuth Hospital, Bayreuth, Bavaria, Germany.
J Biomech. 2019 Sep 20;94:130-137. doi: 10.1016/j.jbiomech.2019.07.029. Epub 2019 Jul 31.
This study evaluated the reactive biomechanical strategies associated with both upper- and lower-body (lead and trail limbs) following the first exposures to (un)expected stepdown at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Eleven healthy adults completed 34 trails per walking velocity over an 8-m, custom-built track with two forceplates embedded in its center. For the expected stepdown, the track was lowered by 0-, -10- and -20-cm from the site of the second forceplate, whereas the unexpected stepdown was created by camouflaging the second forceplate (-10-cm). Two-way repeated-measurement ANOVAs detected no velocity-related effects of stepdown on kinematic and kinetic parameters during lead limb stance-phase, and on the trail limb stepping kinematics. However, analyses of significant interactions revealed greater peak flexion angles across the trunk and the trail limb joints (hip, knee and ankle) in unexpected versus expected stepdown conditions at a faster walking velocity. The -10-cm unexpected stepdown (main effect) had a greater influence on locomotor behavior compared to expected conditions due mainly to the absence of predictive adjustments, reflected by a significant decrease in peak knee flexion, contact time and vertical impulse during stance-phase. Walking faster (main effect) was associated with an increase in hip peak flexion and net anteroposterior impulse, and a decrease in contact time and vertical impulse during stepdown. The trail limb, in response, swung forward faster, generating a larger and faster recovery step. However, such reactive stepping following unexpected stepdown was yet a sparse compensation for an unstable body configuration, assessed by significantly smaller step width and anteroposterior margin-of-stability at foot-contact in the first-recovery-step compared with expected conditions. These findings depict the impact of the expectedness of stepdown onset on modulation of global dynamic postural control for a successful accommodation of (un)expected surface elevation changes in young, healthy adults.
本研究评估了在以舒适（1.22 ± 0.08 m/s）和快速（1.71 ± 0.11 m/s）行走速度首次遇到（预期和意外）下台阶时，上半身和下半身（引导腿和跟随腿）的反应性生物力学策略。11 名健康成年人在一个 8 米长的定制轨道上完成了每个速度下的 34 次试验，该轨道中心嵌入了两个力台。对于预期的下台阶，轨道从第二个力台的位置降低 0、-10 和-20cm，而意外的下台阶是通过伪装第二个力台（-10cm）来创建的。双向重复测量方差分析未检测到步速对引导腿支撑阶段和跟随腿跨步运动学的运动学和动力学参数的影响。然而，对显著交互作用的分析表明，在较快的行走速度下，与预期情况相比，在意外情况下，躯干和跟随腿关节（髋、膝和踝）的峰值屈曲角度更大。由于缺乏预测性调整，10cm 意外下台阶（主要效应）对运动行为的影响大于预期条件，这主要反映在支撑阶段的峰值膝关节屈曲、接触时间和垂直冲量显著减少。行走速度更快（主要效应）与髋关节峰值屈曲和净前后向冲量增加以及接触时间和垂直冲量减少有关。作为响应，跟随腿更快地向前摆动，产生更大更快的恢复步。然而，这种对意外下台阶的反应性跨步仍然是对不稳定身体结构的稀疏补偿，通过在第一次恢复步中与预期条件相比，脚接触时的步宽和前后向稳定裕度明显减小来评估。这些发现描绘了下台阶起始预期性对年轻健康成年人成功适应（预期和意外）表面抬升变化的整体动态姿势控制调节的影响。
