Neurophysiological correlates of aging-related muscle weakness.
Neurophysiological correlates of aging-related muscle weakness.
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DOI：
10.1152/jn.00205.2013
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发表时间：
2013-12
影响因子：
2.5
通讯作者：
E. Plow;D. Cunningham;C. Bonnett;Dina Gohar;M. Bayram;A. Wyant;N. Varnerin;Bernadett Mamone;V. Siemionow;Juliet Hou;A. Machado;G. Yue
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文献类型：
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作者：
E. Plow;D. Cunningham;C. Bonnett;Dina Gohar;M. Bayram;A. Wyant;N. Varnerin;Bernadett Mamone;V. Siemionow;Juliet Hou;A. Machado;G. Yue
与衰老相关的肌肉无力暗示中枢神经退化。然而，初级运动皮层（M1）的作用知之甚少，尽管有证据表明年轻人的力量增长与其适应性有关。我们调查是否肱二头肌在老化的弱点类似地涉及到M1的过程。我们招募了20名年轻（22.6 ± 0.87岁）和28名老年（74.79 ± 1.37岁）右利手参与者。使用经颅磁刺激，二头肌在M1的代表被确定。我们研究了年龄和性别对左肘屈曲强度、肱二头肌自发活动、皮质脊髓兴奋性和输出以及短间隔皮质内和半球间抑制的影响。在老年人中，大脑半球间的抑制作用显著增强（P = 0.047），而强度则趋于降低（P = 0.075）。总体而言，女性较弱（P < 0.001）。M1的过程与二头肌的力量或自愿激活有关，但仅限于老年人。较弱个体的皮质脊髓兴奋性较低（r = 0.38），而皮质脊髓输出、皮质内抑制和半球间抑制在二头肌活动不良的个体中也减少（r = 0.43、0.54和0.38）。较低的皮质内抑制可能反映了对皮质脊髓兴奋性降低的补偿，使较弱的老年人能够在M1中传播活动以招募协同剂并试图维持运动输出。然而，夸大的半球间抑制与先前的证据相冲突，可能与我们较老样本中更大的胼胝体损伤、我们选择的近端与远端肌肉以及在肌肉的休息与活动状态下测量抑制的不同影响有关。总的来说，M1与力量和肌肉激活的年龄特异性关系强调，它的适应性只在必要时才会出现，就像衰老中神经肌肉系统的弱化一样。
Muscle weakness associated with aging implicates central neural degeneration. However, role of the primary motor cortex (M1) is poorly understood, despite evidence that gains in strength in younger adults are associated with its adaptations. We investigated whether weakness of biceps brachii in aging analogously relates to processes in M1. We enrolled 20 young (22.6 ± 0.87 yr) and 28 old (74.79 ± 1.37 yr) right-handed participants. Using transcranial magnetic stimulation, representation of biceps in M1 was identified. We examined the effect of age and sex on strength of left elbow flexion, voluntary activation of biceps, corticospinal excitability and output, and short-interval intracortical and interhemispheric inhibition. Interhemispheric inhibition was significantly exaggerated in the old (P = 0.047), while strength tended to be lower (P = 0.075). Overall, women were weaker (P < 0.001). Processes of M1 related to strength or voluntary activation of biceps, but only in older adults. Corticospinal excitability was lower in weaker individuals (r = 0.38), and corticospinal output, intracortical inhibition and interhemispheric inhibition were reduced too in individuals who poorly activated biceps (r = 0.43, 0.54 and 0.38). Lower intracortical inhibition may reflect compensation for reduced corticospinal excitability, allowing weaker older adults to spread activity in M1 to recruit synergists and attempt to sustain motor output. Exaggerated interhemispheric inhibition, however, conflicts with previous evidence, potentially related to greater callosal damage in our older sample, our choice of proximal vs. distal muscle and differing influence of measurement of inhibition in rest vs. active states of muscle. Overall, age-specific relation of M1 to strength and muscle activation emphasizes that its adaptations only emerge when necessitated, as in a weakening neuromuscular system in aging.