Neuroscience Program and Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, PTC, Butanta, São Paulo, Brazil.
J Neuroeng Rehabil. 2010 Jun 10;7:26. doi: 10.1186/1743-0003-7-26.
High-frequency trains of electrical stimulation applied over the lower limb muscles can generate forces higher than would be expected from a peripheral mechanism (i.e. by direct activation of motor axons). This phenomenon is presumably originated within the central nervous system by synaptic input from Ia afferents to motoneurons and is consistent with the development of plateau potentials. The first objective of this work was to investigate if vibration (sinusoidal or random) applied to the Achilles tendon is also able to generate large magnitude extra torques in the triceps surae muscle group. The second objective was to verify if the extra torques that were found were accompanied by increases in motoneuron excitability.
Subjects (n = 6) were seated on a chair and the right foot was strapped to a pedal attached to a torque meter. The isometric ankle torque was measured in response to different patterns of coupled electrical (20-Hz, rectangular 1-ms pulses) and mechanical stimuli (either 100-Hz sinusoid or gaussian white noise) applied to the triceps surae muscle group. In an additional investigation, Mmax and F-waves were elicited at different times before or after the vibratory stimulation.
The vibratory bursts could generate substantial self-sustained extra torques, either with or without the background 20-Hz electrical stimulation applied simultaneously with the vibration. The extra torque generation was accompanied by increased motoneuron excitability, since an increase in the peak-to-peak amplitude of soleus F waves was observed. The delivery of electrical stimulation following the vibration was essential to keep the maintained extra torques and increased F-waves.
These results show that vibratory stimuli applied with a background electrical stimulation generate considerable force levels (up to about 50% MVC) due to the spinal recruitment of motoneurons. The association of vibration and electrical stimulation could be beneficial for many therapeutic interventions and vibration-based exercise programs. The command for the vibration-induced extra torques presumably activates spinal motoneurons following the size principle, which is a desirable feature for stimulation paradigms.
施加于下肢肌肉的高频电刺激串可产生高于外周机制（即通过直接激活运动轴突）所预期的力。这种现象推测是由 Ia 传入纤维到运动神经元的突触输入引起的，与平台电位的产生一致。这项工作的第一个目标是研究施加于跟腱的振动（正弦或随机）是否也能在比目鱼肌肌群中产生大的附加扭矩。第二个目标是验证是否发现的附加扭矩伴随着运动神经元兴奋性的增加。
受试者（n=6）坐在椅子上，右脚绑在连接扭矩计的踏板上。在不同的电刺激（20-Hz 矩形 1-ms 脉冲）和机械刺激（100-Hz 正弦波或高斯白噪声）模式组合下，测量等长踝关节扭矩。在另外的研究中，在振动刺激之前或之后的不同时间引出 Mmax 和 F 波。
振动爆发可以产生大量的自维持附加扭矩，无论是否同时施加背景 20-Hz 电刺激。附加扭矩的产生伴随着运动神经元兴奋性的增加，因为观察到比目鱼肌 F 波的峰峰值幅度增加。在振动之后进行电刺激的传递对于保持维持的附加扭矩和增加的 F 波是必需的。
这些结果表明，施加背景电刺激的振动刺激会由于脊髓募集运动神经元而产生相当大的力水平（高达约 50%的最大收缩力）。振动和电刺激的结合可能对许多治疗干预和基于振动的运动计划有益。振动诱导的附加扭矩的指令可能根据大小原则激活脊髓运动神经元，这是刺激范式的理想特征。
