Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio 44195, USA.
J Appl Physiol (1985). 2013 Aug 15;115(4):456-67. doi: 10.1152/japplphysiol.00375.2013. Epub 2013 Jun 6.
We investigated the effects of fatigue produced by timed maximal voluntary contraction (MVC) of the index finger of the right hand on performance in MVC and accurate cyclic force production tasks in right-handed young (Young group) and strength-matched elderly (Elderly group) participants. We hypothesized that, before fatigue, the Elderly group would show weaker force-stabilizing synergies and smaller adaptive changes in the synergy index during fatigue. Synergies were defined as covaried adjustments of neural commands to fingers (finger modes) across trials that stabilize total force. Fatigue caused a significant reduction in the MVC, which was larger in the Young group compared with the Elderly group for both fatigued finger (index finger) and four fingers (index, middle, ring, and little fingers pressing together). Indexes of finger enslaving (lack of individuation) increased with fatigue in both groups. The index of force-stabilizing synergies was similar for the two groups before fatigue, while its increase with fatigue was significantly larger in the Elderly group compared with the Young group. We infer that changes in the indexes of finger interaction (enslaving) and coordination (synergy) with age seem to be correlated with changes in muscle strength. This correlation may be causally related to the progressive death of neurons at different levels of the neuromotor hierarchy. The surprisingly large changes in the synergy index with fatigue in older adults suggest that, by itself, aging does not necessarily lead to impairment in synergic control. Strength training may be a method to avoid age-related decrement in finger interaction and coordination.
我们研究了右手食指最大自主等长收缩（MVC）产生的疲劳对右利手年轻（年轻组）和力量匹配的老年（老年组）参与者在 MVC 和准确的周期性力量产生任务中的表现的影响。我们假设，在疲劳之前，老年组在疲劳期间将表现出较弱的力稳定协同作用，以及协同指数的适应性变化较小。协同作用被定义为在试验过程中手指（手指模式）的神经指令的共同调整，以稳定总力。疲劳导致 MVC 显著下降，与老年组相比，年轻组的疲劳手指（食指）和四个手指（食指、中指、环指和小指一起按压）的 MVC 下降幅度更大。在两组中，手指奴役（缺乏个体化）指数随着疲劳而增加。在疲劳之前，两组的力稳定协同指数相似，而与年轻组相比，老年组的协同指数随着疲劳的增加而显著增加。我们推断，手指相互作用（奴役）和协调（协同）指数的变化与年龄有关，这似乎与肌肉力量的变化有关。这种相关性可能与神经运动层次结构不同水平的神经元逐渐死亡有关。老年人的协同指数在疲劳后发生的惊人变化表明，单纯的年龄增长不一定会导致协同控制受损。力量训练可能是避免手指相互作用和协调随年龄增长而下降的一种方法。
