Motor unit function: central descending and sensory reflex modulation

据了解，随着年龄的增长，肌肉力量降低，力量稳定性下降，功能能力下降。这些变化的机制尚不清楚，直到最近才被认识到性别差异。由于有目的的运动仅仅是延长和缩短收缩的组合，在这些简单的活动中，了解激动剂和拮抗剂的MU活性是非常必要的。这些实验的总体目标是确定和确定中枢下行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作用于编码MU输出(MU的招募、放电速率、同步性和连贯性)，然而这种“集体编码”在不同的收缩类型(等长、延长、缩短)中不同，并且随着年龄的变化而改变。此外，由于男性和女性在功能能力和力量方面存在年龄相关性的差异，这两个因素都与MU活动密切相关，因此MU活动可能存在性别差异。据我所知，到目前为止，还没有有针对性地研究健康的年轻和老年女性的MU活动。这些研究不仅将表征女性股四头肌收缩过程中激动剂和拮抗剂MU的活动，而且有助于我们理解感觉反射和棘上下行输入对MU活动和与年龄相关的力量控制变化的贡献。

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.