Lagan James, Lang Peter, Strutton Paul H
The Nick Davey laboratory, Department of Biosurgery and Surgical Technology, Division of Surgery, Oncology, Reproductive biology and Anaesthetics (SORA), Faculty of Medicine, Imperial College London, London W6 8RF, UK.
Clin Neurophysiol. 2008 Dec;119(12):2839-45. doi: 10.1016/j.clinph.2008.09.013. Epub 2008 Oct 30.
Twitch interpolation using transcranial magnetic stimulation (TMS) has recently been used to measure the level of drive from the motor cortex to contracting muscles of the upper and lower limbs, termed voluntary activation. It has yet to be used to assess voluntary activation in trunk muscles. The aim of this study was to assess the feasibility of using TMS to measure voluntary activation in back muscles.
Sixteen healthy subjects performed a series of brief maximal and submaximal isometric contractions of the back extensors during which TMS was delivered to the motor cortex. The evoked (superimposed) twitch was measured using dynamometry and simultaneous surface electromyographic (EMG) recordings were taken from the left and right erector spinae at vertebral level T12. Voluntary activation was derived using the expression: (1-superimposed twitch amplitude/resting twitch amplitude)x100. The resting twitch amplitude was estimated by extrapolation of the linear correlation between voluntary torque and superimposed twitch amplitude to zero torque.
The relationship between superimposed twitch size and voluntary contraction strength for contraction strengths of 50-100% MVC was linear but regression revealed variability between subjects. When data were included from those subjects with a good linear regression fit a strong linear relationship was found for the group means between voluntary contraction strength and voluntary activation (r(2)=1) and superimposed twitch size (r(2)=0.99) for contraction strengths of 50-100% MVC. Voluntary activation was found to be less than maximal (67.71+/-5.22%) during maximal efforts. Time-to-peak amplitude decreased linearly with increasing voluntary torque. The amplitudes of the motor evoked potentials (MEPs) increased with increasing voluntary torque.
Twitch interpolation using TMS can be used to quantify voluntary activation in back extensors. The results of this study reveal that neural drive to the back extensors during strong contractions is submaximal.
The assessment of voluntary activation of the back muscles may aid our understanding of the mechanisms of alteration in control of these muscles implicated in chronic low back pain.
经颅磁刺激（TMS）的抽搐插值法最近已被用于测量从运动皮层到上肢和下肢收缩肌肉的驱动水平，即所谓的自主激活。它尚未被用于评估躯干肌肉的自主激活。本研究的目的是评估使用TMS测量背部肌肉自主激活的可行性。
16名健康受试者进行了一系列背部伸肌的短暂最大和次最大等长收缩，在此期间将TMS施加到运动皮层。使用测力计测量诱发（叠加）抽搐，并从T12椎体水平的左右竖脊肌进行同步表面肌电图（EMG）记录。自主激活通过以下表达式得出：(1 - 叠加抽搐幅度/静息抽搐幅度)×100。静息抽搐幅度通过将自主扭矩与叠加抽搐幅度之间的线性相关性外推至零扭矩来估计。
对于50 - 100%最大自主收缩（MVC）的收缩强度，叠加抽搐大小与自主收缩强度之间的关系呈线性，但回归显示个体间存在变异性。当纳入线性回归拟合良好的受试者的数据时，发现对于50 - 100%MVC的收缩强度，该组均值在自主收缩强度与自主激活（r² = 1）以及叠加抽搐大小（r² = 0.99）之间存在很强的线性关系。发现在最大努力时自主激活小于最大值（67.71±5.22%）。峰值幅度时间随自主扭矩增加呈线性下降。运动诱发电位（MEP）的幅度随自主扭矩增加而增加。
使用TMS的抽搐插值法可用于量化背部伸肌的自主激活。本研究结果表明，在强力收缩期间，对背部伸肌的神经驱动未达到最大值。
对背部肌肉自主激活的评估可能有助于我们理解与慢性下腰痛相关的这些肌肉控制改变的机制。
