The sensory role of muscle for the control of balance

跌倒是老年人的主要问题，65岁以上的人中有30%的人每年摔倒一次或更多，而在85岁以上的S，这一比例上升到50%。跌倒的原因是多因素的，包括感觉和运动两方面的问题。平衡最重要的感觉输入之一来自小腿的小腿肌肉，被称为本体感。有证据表明，老年人本体感觉丧失可能是姿势不稳定的关键原因。然而，肌肉除了作为感觉器官外，还必须产生运动。因此，正在进行的肌肉收缩可能会影响肌肉作为传感器的能力。这反过来又受到脚踝僵硬和整体肌肉力量的个体差异的影响。众所周知，这些因素随着年龄的增长而变化，因此可能会降低肌肉检测身体运动的能力。我们将通过测量老年人(65-85岁)对平衡的本体感觉控制来检验这一假设。最初，我们将检查年轻志愿者(年龄在18-40岁)的平衡，以确定基线表现。特别是，我们将确定脚踝僵硬和肌肉力量的自然变化如何影响安静站立时小腿肌肉发出的感觉信息的质量。为了评估每个志愿者的本体感觉信息的质量，我们将使用超声波测量小腿肌肉的运动，看看肌肉长度在站立时跟踪身体摇摆的情况。这将与姿势稳定性相关。然后我们将确定诸如脚踝僵硬和脚踝力量等机械因素如何影响这种关系。此外，我们将测试这些因素对受试者检测踝关节非常微小旋转的能力的影响。使用一种创新的“虚拟”站立模式，我们将人工操纵力量和脚踝僵硬，以模仿年轻人的衰老表型。一旦我们确定了年轻人的基线表现，我们将研究老年人，以确定已确立的肌肉骨骼变化如何影响对摇摆的本体感觉控制。使用相同的虚拟站立范式，我们将测试人工改善功能的效果。我们方法的优势在于，我们可以在不同群体(年轻人和老年人)之间比较本体感觉，并在受试者中操纵上述因素。这种结合的方法将给我们提供一个全面的图景，说明本体感觉信息是如何在年轻和老年状态下控制平衡的。通过揭示感觉信息用于平衡的机制，我们将更好地理解这些机制如何随着年龄的增长而退化，从而导致姿势不稳定。这将是有益的，既能够更好地识别那些有跌倒风险的人，也能够定制特定的治疗方法来改善平衡功能。

Falls are a major problem for older adults, with 30% of people aged over 65 experiencing 1 or more falls per year, rising to 50% in the over 85's. The reasons for falling are multi-factorial, and include problems with both sensation and movement. One of the most important types of sensory input for balance comes from the calf muscles in the lower leg, termed 'proprioception'. There is evidence to suggest that loss of proprioception in older adults may be a key cause of postural instability. However, muscles must produce movement as well as act as sensory organs. Ongoing muscle contraction may therefore affect the ability of muscle to act as a sensor. This, in turn, is affected by individual variations in ankle stiffness, and overall muscle strength. It is well established that these factors change with age, and this may therefore degrade the ability of the muscle to detect body movement. We will test this hypothesis by measuring proprioceptive control of balance in older adults (aged 65-85). Initially, we will examine balance in younger volunteers (aged 18-40) to establish baseline performance. In particular, we will determine how natural variations in ankle stiffness and muscle strength affect the quality of sensory information emanating from the calf muscles during quiet standing. To assess the quality of proprioceptive information in each volunteer, we will use ultrasound to measure calf muscle movement to see how well muscle length tracks body sway when standing. This will be correlated with postural stability. We will then determine how mechanical factors such as ankle stiffness and ankle strength affect this relationship. Furthermore, we will test the influence of these factors upon the ability of subjects to detect very small rotations at the ankle joint. Using an innovative 'virtual' standing paradigm, we will then artificially manipulate strength and ankle stiffness to mimic the ageing phenotype in the young. Once we have established baseline performance in the young, we will study older adults to determine how the well-established musculoskeletal changes affect proprioceptive control of sway. Using the same virtual standing paradigm, we will test the effect of artificially improving function. The strength of our approach is that we can compare proprioception between groups (young vs old) as well as manipulate the above factors within subjects. This combined approach will give us a comprehensive picture of how proprioceptive information is used to control balance, both in the young and aged state. By revealing the mechanisms by which sensory information is used for balance, we will better understand how these mechanisms degrade with age leading to postural instability. This will be of benefit both in being able to better identify those at risk of falling, and being able to tailor specific therapies to improve balance function.