School of Healthcare Science, Manchester Metropolitan University, Manchester, M15GD, UK.
Department of Systems Design Engineering, University of Waterloo, Ontario, N2L 3G1, Canada.
Eur J Appl Physiol. 2018 Apr;118(4):767-775. doi: 10.1007/s00421-018-3811-5. Epub 2018 Jan 22.
Current methods for estimating muscle motor unit (MU) number provide values which are remarkably similar for muscles of widely differing size, probably because surface electrodes sample from similar and relatively small volumes in each muscle. We have evaluated an alternative means of estimating MU number that takes into account differences in muscle size.
Intramuscular motor unit potentials (MUPs) were recorded and muscle cross-sectional area (CSA) was measured using MRI to provide a motor unit number estimate (iMUNE). This was compared to the traditional MUNE method, using compound muscle action potentials (CMAP) and surface motor unit potentials (sMUPs) recorded using surface electrodes. Data were collected from proximal and distal regions of the vastus lateralis (VL) in young and old men while test-retest reliability was evaluated with VL, tibialis anterior and biceps brachii.
MUPs, sMUPs and CMAPs were highly reliable (r = 0.84-0.91). The traditional MUNE, based on surface recordings, did not differ between proximal and distal sites of the VL despite the proximal CSA being twice the distal CSA. iMUNE, however, gave values that differed between young and old and were proportional to the muscle size.
When evaluating the contribution that MU loss makes to muscle atrophy, such as in disease or ageing, it is important to have a method such as iMUNE, which takes into account any differences in total muscle size.
目前用于估计肌肉运动单位（MU）数量的方法提供了非常相似的值，这些值适用于大小差异很大的肌肉，这可能是因为表面电极在每个肌肉中采样相似且相对较小的体积。我们评估了一种替代方法来估计 MU 数量，该方法考虑了肌肉大小的差异。
使用 MRI 记录肌内运动单位电位（MUP）并测量肌肉横截面积（CSA），以提供运动单位数量估计值（iMUNE）。将其与传统的使用表面电极记录的复合肌肉动作电位（CMAP）和表面运动单位电位（sMUP）的 MUNE 方法进行比较。从年轻男性和老年男性的股外侧肌（VL）的近端和远端区域收集数据，同时评估 VL、胫骨前肌和肱二头肌的测试-重测可靠性。
MUP、sMUP 和 CMAP 具有高度可靠性（r=0.84-0.91）。尽管近端 CSA 是远端 CSA 的两倍，但基于表面记录的传统 MUNE 在 VL 的近端和远端部位之间没有差异。然而，iMUNE 的值在年轻和老年之间有所不同，并且与肌肉大小成正比。
在评估 MU 损失对肌肉萎缩（如疾病或衰老）的贡献时，重要的是要有一种方法，如 iMUNE，该方法考虑了总肌肉大小的任何差异。
