PDF(Pubmed)
Abstract：
Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoVISI), and intermittent firing] modulated with leaning direction. The purpose of this study was to examine whether older adults exhibited this regional recruitment of MUs and firing behaviors. Seventeen older adults (aged 74.8 ± 5.3 yr) stood on a force platform and maintained their center of pressure leaning in five directions. High-density surface electromyography recordings from the triceps surae were decomposed into single MU action potentials. A MU tracking analysis identified groups of MUs as being common or unique across the leaning directions. Although leaning in different directions did not affect the AFR and CoVISI of common units (P > 0.05), the unique units responded to the leaning directions by increasing AFR and CoVISI, albeit modestly (F = 18.51, P < 0.001). The unique units increased their intermittency with forward leaning (F = 9.22, P = 0.003). The mediolateral barycenter positions of MU activity in both subpopulations were found in similar locations for all leaning directions (P > 0.05). These neuromuscular changes may contribute to the reduced balance performance seen in older adults.NEW & NOTEWORTHY In this study, we observed differences in motor unit recruitment and firing behaviors of distinct subpopulations of motor units in the older adult triceps surae muscle from those observed in the young adult. Our results suggest that the older adult central nervous system may partially lose the ability to regionally recruit and differentially control motor units. This finding may be an underlying cause of balance difficulties in older adults during directionally challenging leaning tasks.
摘要：
衰老与神经肌肉系统变化有关，这可能对运动单位（MU）的招募和射击行为产生影响。在以往的研究中,我们观察到，年轻人在涉及向多个方向倾斜的任务中招募肱三头肌MU的亚群：在不同的倾斜方向上活跃的常见单位，以及仅在一个倾斜方向活跃的独特单位。Further,MU子群体射击行为(平均射击率(AFR)，变异系数(CoVisi)和间歇发射)随倾斜方向调制。这项研究的目的是检查老年人是否表现出这种区域招募和MU控制策略。17名老年人（年龄为74.8±5.3岁）站在力量平台上，并保持其压力中心向5个方向倾斜。来自肱三头肌的高密度表面肌电图记录被分解为单个MU动作电位。MU跟踪分析将MU组识别为在倾斜方向上是共同的或唯一的。虽然向不同方向倾斜并不影响普通单位的AFR和CoVisi(p>0.05)，独特的单位通过增加AFR和CoVisi来响应倾斜方向，虽然适度（F=18.51，p<0.001）。独特的单元随着前倾而增加了间歇性（F=9.22，p=0.003）。对于所有倾斜方向，在两个亚群中MU活动的中-外侧重心位置均在相似位置发现（p>0.05）。这些神经肌肉变化可能导致老年人的平衡表现下降。
