LIMB COLLAPSE AND FALLS AMONG ELDERLY

保护性步进是一种常见的平衡恢复反应。然而，保护性步进失败的潜在机制在很大程度上是未知的。我们正在开创一系列工作，专注于保护性步进失败的准确原因。我们期望我们的研究能为未来的体育康复中基于特异性原则的干预铺平道路。我们将首先证明，肢体塌陷是保护性踏步失败的主要原因，年龄和性别是成功尝试在肢体塌陷后恢复平衡的关键决定因素。我们将测试以下假设：在日常活动的执行过程中，所有受试者都会发生肢体塌陷，而且比年轻人(22-45岁)和男性成年人更多的老年人(65-80岁)和女性无法从肢体塌陷中恢复过来。为了了解为什么一些年长的受试者能够从肢体塌陷中恢复，而另一些受试者却无法恢复，我们接下来将确定肢体塌陷的生物力学原因。我们将验证这样的假设：在一些研究生受试者中，肢体塌陷是不可避免的，因为支撑膝关节(而不是髋关节或脚踝)未能产生扭矩来达到恢复阈值，而且这个阈值是可预测的。为了找到增强个体对肢体塌陷的抵抗力的具体方法，我们将研究从肢体塌陷中恢复的神经肌肉机制。我们将检验这样的假设，即伸展扭矩不足是由于类似于惊吓或其他相关反应的某些成分的长时间反射性中介抑制造成的，而不是由于在重心垂直下降的关键时间窗口期间前馈编程失败造成的。我们的长期目标是开发康复计划，促进和加强老年人自身对因肢体崩溃而发生的灾难性跌倒的抵抗力。其结果将是降低医疗保健费用和不必要的伤害，目前这些费用降低了灾难性坠落受害者的行动能力和生活质量。

Protective stepping is a common response used for balance recovery. Nevertheless, the mechanisms underlying situations where protective stepping fails are largely unexplored and unknown. We are pioneering a line of work that focuses on the precise causes for failure in protective stepping. We expect our research to pave the way for future interventions based on the specificity principle in physical rehabilitation. We will first demonstrate that limb collapse is the major cause for failure in protective stepping, and that age and gender are critical determinants in successful attempts to regain balance after limb collapse. We will test the hypotheses that limb collapse will occur in all subjects during unexpected slipping in the execution of a daily activity, and that a greater number of older adults (ages 65-80 years) and female adults will not be able to recover from limb collapse than young adults (ages 22-45 years) and male adults. In order to understand why some older subjects are able to recover from limb collapse while other fail to do so, we will next determine the biomechanical causes for limb collapse. We will test the hypotheses that limb collapse is inevitable in some graduate subjects because the supporting knee (instead of hip or ankle) has failed to generate torques to reach threshold value for recovery, and furthermore that this threshold is predictable. In order to find the specific means to strengthen an individual's resistance to limb collapse, we will then examine the neuromuscular mechanisms for recovery from limb collapse. We will test the hypotheses that insufficient extension torques result from a prolonged, reflexively mediated inhibition similar to some component of startle or other related responses, rather than from a failure of feed-forward programming during the critical time-window of center of mass vertical descent. Our long-term goal is to develop rehabilitation programs that will facilitate and fortify elderly individuals' own resistance to catastrophic falls due to limb collapse. The results will be a reduction in both costs of health care and in unnecessary injury that currently lowers the mobility and the quality of life of victims of catastrophic falls.