Canadian Centre for Activity and Aging, School of Kinesiology, University of Western Ontario, London, ON, Canada.
Acta Physiol (Oxf). 2010 Sep;200(1):45-55. doi: 10.1111/j.1748-1716.2010.02100.x. Epub 2010 Feb 12.
Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 +/- 4 years) and six young (24 +/- 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups.
Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force-frequency relationship and MUDRs from sub-maximal to maximal intensities were assessed in the elbow flexors and extensors.
Both flexor and extensor MVCs were significantly (P < 0.05) less (approximately 42% and approximately 46% respectively) in the old than in the young. Contractile speeds and the force-frequency relationship did not show any age-related differences (P > 0.05). For the elbow flexors contraction duration was approximately 139 ms and for the extensors it was approximately 127 ms for both age groups (P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (approximately 10% to approximately 36%) in the old than in the young (P < 0.01). These age-related differences were larger for biceps (Cohen's d = 8.25) than triceps (Cohen's d = 4.79) brachii.
Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed.
人类神经肌肉系统的健康成人衰老由多种变化组成，包括萎缩、无力和运动迟缓，表现为较低的运动神经元输出，即较低的运动单位放电率（MUDRs）。后一种观察结果主要来自手部和下肢肌肉。本研究旨在确定肱二头肌和肱三头肌的收缩性能以及 6 名老年人（83±4 岁）和 6 名年轻人（24±1 岁）的 MUDRs 在多大程度上受到年龄的影响，以及两组肌肉是否存在相似的适应性。
评估了肱二头肌和肱三头肌的最大等长随意收缩（MVC）、自愿激活、抽搐收缩性能、力频关系和从亚最大到最大强度的 MUDRs。
老年人的肱二头肌和肱三头肌 MVC 均明显（P<0.05）低于年轻人（分别约为 42%和 46%）。收缩速度和力频关系没有显示出任何与年龄相关的差异（P>0.05）。对于肱二头肌，收缩持续时间约为 139ms，对于肱三头肌，两组的收缩持续时间约为 127ms（P>0.05）。从 25%MVC 到最大的平均 MUDRs 在老年人中较低（约为 10%至 36%），明显低于年轻人（P<0.01）。这些与年龄相关的差异在肱二头肌（Cohen's d=8.25）中比肱三头肌（Cohen's d=4.79）更大。
因此，至少对于近端上肢肌肉，随着健康成人的衰老，平均最大 MUDR 减少是肌肉特异性的，与收缩速度没有很强的相关性。
