School of Engineering, Design and Technology, University of Bradford, Bradford, West Yorkshire, UK.
Exp Gerontol. 2013 Feb;48(2):283-9. doi: 10.1016/j.exger.2012.11.003. Epub 2012 Nov 22.
When descending stairs bodyweight becomes supported on a single limb while the forwards-reaching contralateral limb is lowered in order to make contact with the step below. This is associated with lowering of the centre of mass (CoM), which in order to occur in a controlled manner, requires increased ankle and knee joint torque production relative to that in overground walking. We have previously shown that when descending steps or stairs older people operate at a higher proportion of their maximum eccentric capacity and at, or in excess of the maximum passive reference joint range of motion. This suggests they have reduced and/or altered control over their CoM and we hypothesised that this would be associated with alterations in muscle activity patterns and in the CoM vertical acceleration and velocity profiles during both the lowering and landing phases of stair descent. 15 older (mean age 75 years) and 17 young (mean age 25 years) healthy adults descended a 4-step staircase, leading with the right limb on each stair, during which CoM dynamics and electromyographic activity patterns for key lower-limb muscles were assessed. Maximum voluntary eccentric torque generation ability at the knee and ankle was also assessed. Older participants compared to young participants increased muscle co-contraction relative duration at the knee and ankle of the trailing limb so that the limb was stiffened for longer during descent. As a result older participants contacted the step below with a reduced downwards CoM velocity when compared to young participants. Peak downwards and peak upwards CoM acceleration during the descent and landing phases respectively, were also reduced in older adults compared to those in young participants. In contrast, young participants descended quickly onto the step below but arrested their downward CoM velocity sooner following landing; a strategy that was associated with longer relative duration lead-limb plantar flexor activity, increased peak upwards CoM acceleration, and a reduced landing duration. These results suggest that a reduced ability to generate high eccentric torque at the ankle in the forward reaching limb is a major factor for older participants adopting a cautious movement control strategy when descending stairs. The implications of this CoM control strategy on the incidences of falling on stairs are discussed.
当从楼梯上下来时，身体的重量会支撑在单腿上，同时向前伸展的对侧肢体降低，以便与下方的台阶接触。这与重心（CoM）的降低有关，为了以受控的方式发生，需要相对于在地面行走时增加踝关节和膝关节的扭矩产生。我们之前已经表明，当老年人上下楼梯或台阶时，他们的最大离心能力的比例更高，并且达到或超过最大被动参考关节运动范围。这表明他们对 CoM 的控制能力降低了和/或改变了，我们假设这将与肌肉活动模式以及 CoM 的垂直加速度和速度曲线在楼梯下降的降低和着陆阶段的变化有关。15 名老年人（平均年龄 75 岁）和 17 名年轻人（平均年龄 25 岁）健康成年人在每级楼梯上用右侧肢体领先，在此期间评估 CoM 动力学和关键下肢肌肉的肌电图活动模式。还评估了膝关节和踝关节的最大自主离心扭矩产生能力。与年轻参与者相比，老年参与者增加了尾随肢体的膝关节和踝关节的肌肉共同收缩相对持续时间，因此在下降过程中肢体变硬的时间更长。结果，与年轻参与者相比，老年参与者在接触下方台阶时 CoM 速度下降幅度较小。与年轻参与者相比，老年人在下降和着陆阶段的 CoM 加速度峰值分别向下和向上也降低。相比之下，年轻参与者迅速下降到下方的台阶，但在着陆后更早地停止向下的 CoM 速度；这是一种策略，与较长的相对持续时间的导腿跖屈肌活动、增加的 CoM 加速度峰值以及减少的着陆持续时间相关。这些结果表明，向前伸展的肢体中脚踝产生高离心扭矩的能力下降是老年人在上下楼梯时采用谨慎运动控制策略的主要因素。讨论了这种 CoM 控制策略对在楼梯上摔倒的发生率的影响。
