Clark Brian C, Taylor Janet L, Hong S Lee, Law Timothy D, Russ David W
Neuroscience Research Australia and the University of New South Wales, Randwick, Australia.
Ohio Musculoskeletal and Neurological Institute (OMNI) at Ohio University, Athens. Department of Family Medicine at Ohio University, Athens.
J Gerontol A Biol Sci Med Sci. 2015 Sep;70(9):1112-9. doi: 10.1093/gerona/glv030. Epub 2015 Apr 1.
Weakness predisposes seniors to a fourfold increase in functional limitations. The potential for age-related degradation in nervous system function to contribute to weakness and physical disability has garnered much interest of late. In this study, we tested the hypothesis that weaker seniors have impairments in voluntary (neural) activation and increased indices of GABAergic inhibition of the motor cortex, assessed using transcranial magnetic stimulation.
Young adults (N = 46; 21.2±0.5 years) and seniors (N = 42; 70.7±0.9 years) had their wrist flexion strength quantified along with voluntary activation capacity (by comparing voluntary and electrically evoked forces). Single-pulse transcranial magnetic stimulation was used to measure motor-evoked potential amplitude and silent period duration during isometric contractions at 15% and 30% of maximum strength. Paired-pulse transcranial magnetic stimulation was used to measure intracortical facilitation and short-interval and long-interval intracortical inhibition. The primary analysis compared seniors to young adults. The secondary analysis compared stronger seniors (top two tertiles) to weaker seniors (bottom tertile) based on strength relative to body weight.
The most novel findings were that weaker seniors exhibited: (i) a 20% deficit in voluntary activation; (ii) ~20% smaller motor-evoked potentials during the 30% contraction task; and (iii) nearly twofold higher levels of long-interval intracortical inhibition under resting conditions.
These findings indicate that weaker seniors exhibit significant impairments in voluntary activation, and that this impairment may be mechanistically associated with increased GABAergic inhibition of the motor cortex.
身体虚弱会使老年人功能受限的风险增加四倍。近年来，与年龄相关的神经系统功能退化导致身体虚弱和残疾的可能性引起了广泛关注。在本研究中，我们检验了以下假设：身体较弱的老年人存在随意（神经）激活受损以及运动皮层γ-氨基丁酸（GABA）能抑制指标增加的情况，这些通过经颅磁刺激进行评估。
对年轻成年人（N = 46；21.2±0.5岁）和老年人（N = 42；70.7±0.9岁）的腕部屈曲力量以及随意激活能力（通过比较随意力和电诱发力）进行量化。在最大力量的15%和30%进行等长收缩时，使用单脉冲经颅磁刺激测量运动诱发电位幅度和静息期持续时间。使用双脉冲经颅磁刺激测量皮质内易化以及短间隔和长间隔皮质内抑制。主要分析将老年人与年轻成年人进行比较。次要分析根据相对于体重的力量，将较强的老年人（前两个三分位数）与较弱的老年人（最低三分位数）进行比较。
最主要的新发现是，较弱的老年人表现出：（i）随意激活能力有20%的缺陷；（ii）在30%收缩任务期间运动诱发电位小约20%；（iii）在静息状态下长间隔皮质内抑制水平几乎高出两倍。
这些发现表明，较弱的老年人在随意激活方面存在显著损伤，并且这种损伤可能在机制上与运动皮层GABA能抑制增加有关。
