Sosnoff Jacob J, Vaillancourt David E, Newell Karl M
Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Neurophysiol. 2004 Jan;91(1):172-81. doi: 10.1152/jn.00613.2003. Epub 2003 Sep 24.
The current study examined the influence of aging on the oscillatory activity of a population of motor units during rhythmical force production. Previously, it has been shown that aging humans have greater low-frequency and less high-frequency electromyographic (EMG) activity during constant and slow ramp force contractions. We hypothesized that more rapid force contractions would reverse the established finding of reduced high- and greater low-frequency EMG activity to greater high- and reduced low-frequency EMG activity in older adults. Intramuscular EMG activity and effector force were recorded while 45 human subjects (20-31 and 60-88 yr of age) rhythmically produced force at four distinct frequencies (1-4 Hz) and two force levels (5 and 25% maximal voluntary contraction). Spectral and coherence analyses were performed on the force output and EMG activity. In the 3- and 4-Hz targets, the older adults had greater 35- to 50-Hz and reduced 0- to 5-Hz EMG activity compared with the young adults. There was greater EMG-force coherence in the 0- to 5-Hz bandwidth for the young subjects. No systematic age difference in the phase relationship between the EMG and force signals were found. Higher frequency force contractions reversed the previously established aging differences in the relative contribution of low- and high-frequency EMG activity. Thus the frequency properties of the task goals channel the relative contribution of low and high EMG activity. Furthermore, it is proposed that aging humans lose the adaptive capability to coordinate the excitatory and inhibitory activity of multiple neural oscillators.
本研究考察了衰老对有节奏地产生力量过程中运动单位群体振荡活动的影响。此前研究表明，在持续和缓慢递增力量收缩过程中，衰老的人类具有更大的低频和更小的高频肌电图（EMG）活动。我们假设，更快的力量收缩会扭转之前已确立的发现，即在老年人中高频EMG活动减少而低频EMG活动增加的情况，使其变为高频EMG活动增加而低频EMG活动减少。在45名人类受试者（年龄在20 - 31岁和60 - 88岁之间）以四种不同频率（1 - 4Hz）和两种力量水平（最大自主收缩的5%和25%）有节奏地产生力量时，记录了肌肉内EMG活动和效应器力量。对力量输出和EMG活动进行了频谱和相干分析。在3Hz和4Hz目标频率下，与年轻成年人相比，老年人具有更大的35至50Hz的EMG活动以及更低的0至5Hz的EMG活动。年轻受试者在0至5Hz带宽内具有更大的EMG - 力量相干性。未发现EMG和力量信号之间相位关系存在系统性年龄差异。更高频率的力量收缩扭转了之前确立的衰老在低频和高频EMG活动相对贡献方面的差异。因此，任务目标的频率特性决定了低频和高频EMG活动的相对贡献。此外，有人提出衰老的人类失去了协调多个神经振荡器兴奋和抑制活动的适应能力。
