Kirk Eric A, Gilmore Kevin J, Rice Charles L
Neuromuscular Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario , Canada.
Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario , London, Ontario , Canada.
J Neurophysiol. 2018 Aug 1;120(2):480-488. doi: 10.1152/jn.00794.2017. Epub 2018 Apr 18.
Despite the life-long importance for posture and locomotion, neuromuscular properties of the hamstrings muscle have not been explored with adult aging. The purpose of this study was to assess and compare age-related effects on contractile function, spinal motor neuron output expressed as motor unit (MU) discharge rates in the hamstrings of 11 young (26 ± 4 yr) and 10 old (80 ± 5 yr) men. Maximal voluntary isometric contractions (MVC), stimulated contractile properties, and surface and intramuscular electromyography (EMG) from submaximal to MVC were recorded in the biceps femoris (BF) and semimembranosus-semitendinosus (SS) muscles. MVC torque was ~50% less in the old with both age groups attaining ≥93% mean voluntary activation. Evoked twitches in the old were ~50% lower in amplitude and >150% longer in duration compared with those in the young. At successive voluntary contractions of 25, 50, and 100% MVC, MU discharge rates were up to 45% lower in old, with no differences in relative submaximal surface EMG between age groups. Furthermore, the old had significantly lower MU discharge rates in the SS at all contraction intensities compared with the BF muscle. Men in their 8th to 10th decades of life demonstrate substantially lower strength and MU discharge rates in this functionally important large lower limb muscle group, with greater age-related effect on discharge rates in the medial hamstrings. These findings, compared with those in other muscles studied, highlight that the neuromuscular properties of limb muscles, and indeed within functionally similar portions of a muscle group, are not all affected equally by the aging process. NEW & NOTEWORTHY In the hamstrings, we found that both contractile function and motor unit discharge rates across the range of voluntary intensities were lower in the old. The differences in discharge rates due to age were greater in the medial hamstrings muscle group compared with the lateral hamstrings. Compared with previous studies, these results highlight that not all muscles are affected equally by aging and there may be compartmental differences within functionally similar muscles.
尽管腘绳肌的神经肌肉特性对姿势和运动具有终身重要性，但尚未对成年衰老过程中的相关特性进行研究。本研究旨在评估和比较年龄对11名年轻男性（26±4岁）和10名老年男性（80±5岁）腘绳肌收缩功能的影响，以运动单位（MU）放电率表示脊髓运动神经元输出。记录股二头肌（BF）和半膜肌-半腱肌（SS）从次最大收缩到最大自主等长收缩（MVC）的最大自主等长收缩（MVC）、刺激收缩特性以及表面和肌内肌电图（EMG）。老年组的MVC扭矩比年轻组低约50%，两个年龄组的平均自主激活率均≥93%。与年轻组相比，老年组诱发的抽搐幅度低约50%，持续时间长>150%。在25%、50%和100%MVC的连续自主收缩中，老年组的MU放电率低至45%，各年龄组次最大表面EMG相对值无差异。此外，在所有收缩强度下，老年组SS的MU放电率均显著低于BF肌肉。80至100岁的男性在这个功能重要的大型下肢肌肉群中表现出明显更低的力量和MU放电率，与年龄相关的内侧腘绳肌放电率影响更大。与其他研究的肌肉相比，这些发现突出表明，肢体肌肉的神经肌肉特性，以及实际上在肌肉群功能相似部分内的特性，并非都受到衰老过程的同等影响。新发现与值得注意的是，在腘绳肌中，我们发现老年组在整个自主强度范围内的收缩功能和运动单位放电率均较低。与外侧腘绳肌相比，内侧腘绳肌组因年龄导致的放电率差异更大。与先前的研究相比，这些结果突出表明并非所有肌肉都受到衰老的同等影响，并且在功能相似的肌肉内可能存在分区差异。
