Doherty T J, Vandervoort A A, Taylor A W, Brown W F
Faculty of Kinesiology, Department of Physical Therapy, Elborn College, London, Ontario, Canada.
J Appl Physiol (1985). 1993 Feb;74(2):868-74. doi: 10.1152/jappl.1993.74.2.868.
The influence of age-associated motor unit loss on contractile strength was investigated in a representative sample of healthy, active young and older men and women. In 24 younger subjects (22-38 yr) and 20 older subjects (60-81 yr) spike-triggered averaging was employed to extract a sample of surface-recorded single motor unit action potentials (S-MUAPs) from the biceps brachii and brachialis muscles. The amplitude of the maximum compound muscle action potential of the biceps brachii and brachialis muscles was divided by the mean S-MUAP amplitude to estimate the numbers of motor units present. The maximum isometric twitch contraction (MTC) and maximum voluntary contraction (MVC) of the elbow flexors were also recorded in 18 of the younger subjects and in all older subjects. The estimated numbers of motor units were significantly reduced (47%, P < 0.001) in older subjects with a mean value of 189 +/- 77 compared with a mean of 357 +/- 97 in younger subjects. The sizes of the S-MUAPs, however, were significantly larger in older subjects (23%, P < 0.01). Significant but less marked age-associated reductions in the MTC (33%, P < 0.05) and MVC (33%, P < 0.001) were also found and were similar for both men and women. These results suggest that motor unit losses, even in healthy active individuals, are a primary factor in the age-associated reductions in contractile strength.
在健康、活跃的年轻和老年男性及女性的代表性样本中，研究了与年龄相关的运动单位损失对收缩力的影响。对24名年轻受试者（22 - 38岁）和20名老年受试者（60 - 81岁），采用触发脉冲平均法从肱二头肌和肱肌中提取表面记录的单个运动单位动作电位（S - MUAPs）样本。将肱二头肌和肱肌的最大复合肌肉动作电位的幅度除以平均S - MUAP幅度，以估计存在的运动单位数量。还对18名年轻受试者和所有老年受试者记录了肘屈肌的最大等长收缩（MTC）和最大自主收缩（MVC）。与年轻受试者平均357±97相比，老年受试者的估计运动单位数量显著减少（47%，P < 0.001），平均值为189±77。然而，老年受试者的S - MUAPs大小显著更大（23%，P < 0.01）。还发现MTC（33%，P < 0.05）和MVC（3%，P < 0.001）存在与年龄相关的显著但不太明显的降低，且男性和女性相似。这些结果表明，即使在健康活跃的个体中，运动单位损失也是与年龄相关的收缩力降低的主要因素。
