van Dieën Jaap H, Spanjaard Marcel, Konemann Reinier, Bron Lennart, Pijnappels Mirjam
Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit Amsterdam, NL-1081 BT Amsterdam, The Netherlands.
J Biomech. 2007;40(16):3641-9. doi: 10.1016/j.jbiomech.2007.06.009. Epub 2007 Jul 17.
Stepping down an elevation in ongoing gait is a common task that can cause falls when the level change is unexpected. The aim of this study was to compare expected and unexpected stepping down. We hypothesized that unexpected stepping would lead to loss of control over the movement and potentially falls due to buckling of the leading leg at landing. Ten male subjects repeatedly walked over a platform on which they stepped down an expected 10-cm height difference. In 5 out of 50 trials, the height difference was encountered unexpectedly early. Kinematics and ground reaction forces under both feet were measured during the stride in which the height difference was negotiated. Stepping down involved a substantial increase in forward horizontal and angular momenta (approximately 40 Ns and 20 N ms). In expected stepping down, step length was significantly increased (17%), which allowed control of these forward horizontal and angular momenta immediately following landing. In unexpected stepping down, the time between expected ground contact and actual ground contact (110 ms) appeared too short to substantially adjust leg movement and increase step length. Although buckling of the leg did not occur, presumably due to its more vertical orientation at landing, momentum could not be sufficiently attenuated at landing, but a fall was prevented by a rapid step of the trailing limb. The lack of control of momentum might cause a fall, when the capacity to make such a rapid step falls short, as in the elderly, or when the height difference is larger.
在持续行走过程中走下一定高度是一项常见任务，当高度变化出乎意料时可能导致跌倒。本研究的目的是比较预期和意外走下高度的情况。我们假设意外走下会导致对动作失去控制，并可能由于着地时领先腿的屈曲而跌倒。十名男性受试者反复走过一个平台，在该平台上他们走下预期的10厘米高度差。在50次试验中有5次，高度差意外地提前出现。在走过高度差的那一步中测量了双脚的运动学和地面反作用力。走下高度涉及向前水平动量和角动量的大幅增加（约40 Ns和20 N·ms）。在预期走下时，步长显著增加（17%），这使得在着地后能立即控制这些向前水平动量和角动量。在意外走下时，预期地面接触与实际地面接触之间的时间（110毫秒）似乎太短，无法充分调整腿部动作并增加步长。尽管腿部没有发生屈曲，可能是由于着地时其更垂直的方向，但着地时动量无法充分衰减，不过后肢的快速一步防止了跌倒。当做出这种快速一步的能力不足时，如在老年人中，或者当高度差更大时，动量缺乏控制可能会导致跌倒。
