Motor unit function: central descending and sensory reflex modulation

随着年龄的增长，肌肉力量下降，力量稳定性下降，功能能力下降。这些变化的机制尚未明确阐明，直到最近才认识到性别差异。由于有目的的运动仅仅是延长和缩短收缩的组合，因此了解激动剂和拮抗剂在这些简单活动中的MU活性是必要的。这些实验的总体目标是确定和确定中央下降和感觉反射通路对运动神经元活动的调节以及随后对年轻和老年女性股四头肌力量控制的影响。我们的工作假设是，感觉反馈和中央下行通路共同编码MU输出（MU的招募、放电率、同步和一致性），然而这种“集体编码”在收缩类型（等距收缩、延长收缩、缩短收缩）之间是不同的，并且随着年龄的增长而改变。此外，由于男性和女性在功能能力和力量方面存在与年龄相关的不同衰退，而这两种因素都与MU活动密切相关，因此MU活动可能存在性别差异。据我所知，迄今为止，还没有专门研究过健康的年轻和老年妇女的MU活性。这些研究不仅将描述女性股四头肌收缩过程中激动剂和拮抗剂的MU活性，而且有助于我们理解感觉反射和椎上下行输入对MU活性的贡献以及力控制中与年龄相关的改变。

It is understood that muscle strength is lower, force steadiness decreases and functional ability declines with advancing age.  The mechanisms of these changes have not been clearly elucidated and until recently gender differences were not recognized.  Because purposeful movement is merely a combination of lengthening and shortening contractions, it is imperative to understand MU activity of the agonist and antagonist during these simple activities. The overall objectives of these experiments are to identify and determine the contributions of central descending and sensory reflex pathways to the modulation of motor neuron activity and subsequent effect on force control in the quadriceps of young and old women. Our working hypothesis is that sensory feedback and central descending pathways work collectively to code MU output (recruitment, discharge rate, synchronization and coherence of MUs), however this 'collective coding' differs between contraction types (isometric, lengthening, shortening) and is altered with age. Moreover, because there are differential age-related declines between men and women in functional ability and strength and both of these elements are closely linked to MU activity it is plausible that a gender difference in MU activity might exist.  To my knowledge, to date, MU activity has not been purposely studied in healthy young and old women.  These studies will not only characterize agonist and antagonist MU activity during anisometric quadriceps contractions in women, but contribute to our understanding of the contribution of sensory reflex and supraspinal descending input on MU activity and age-related alterations in force control.