Twitch interpolation in human muscles: Mechanisms and implications for measurement of voluntary activation
Twitch interpolation in human muscles: Mechanisms and implications for measurement of voluntary activation
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DOI：
10.1152/jn.1999.82.5.2271
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发表时间：
1999-11-01
影响因子：
2.5
通讯作者：
Gandevia, SC
中科院分区：
文献类型：
--
作者：
Herbert, RD;Gandevia, SC
在最大的随意收缩时，给肌肉神经的电刺激通常会产生类似抽搐的力量增加。这种“内插抽搐”的振幅被广泛用于测量肌肉的自愿“激活”。在本研究中，我们使用了一个人体拇内收肌运动神经元池的计算机模型来研究影响内插抽搐的因素。对自然发生的正正交电位的反正交遮挡进行了模拟，但没有对刺激的反射效应进行模拟。在模拟中，反向碰撞发生的概率在16%（早期运动神经元）和接近100%（晚期运动神经元）之间。除了在中等收缩强度下内插抽搐的幅度被略微高估外，该模型在全自主力范围内对内插抽搐上升相位的幅度和时间过程的实验数据有很好的预测。小的内插抽搐（静息抽搐的4.7%）在模拟最大自主收缩中很明显，但当平均峰值放电率增加到相似的60 Hz时，几乎完全闭塞。模拟的内插抽动没有表现出明显的抽动峰值后的力下降，当模型中排除反向碰撞时，内插抽动幅度略有增加，力达到峰值的时间延长。这些发现表明，反变换和反射效应都降低了内插抽搐的幅度，并有助于抽搐后的力下降。内插抽动的幅度与运动神经元池的“兴奋”呈非线性关系，因此在接近最大收缩强度时（>最大自主力的90%），兴奋的增加只会对内插抽动幅度产生很小的变化。因此，在接近最大力的情况下，抽搐插值可能不能提供运动神经元兴奋的灵敏测量。在疲劳和各种病理中观察到的内插抽搐幅度的增加可能反映了运动神经元池兴奋的大量减少。
An electrical stimulus delivered to a muscle nerve during a maximal voluntary contraction usually produces a twitchlike increment in force. The amplitude of this "interpolated twitch" is widely used to measure voluntary "activation" of muscles. In the present study, a computer model of the human adductor pollicis motoneuron pool was used to investigate factors that affect the interpolated twitch. Antidromic occlusion of naturally occurring orthodromic potentials was modeled, but reflex effects of the stimulus were not. In simulations, antidromic collisions occurred with probabilities of between similar to 16% (in early recruited motoneurons) and nearly 100% (in late recruited motoneurons). The model closely predicted experimental data on the amplitude and time course of the rising phase of interpolated twitches over the full range of voluntary forces, except that the amplitude of interpolated twitches was slightly overestimated at intermediate contraction intensities. Small interpolated twitches (4.7% of the resting twitch) were evident in simulated maximal voluntary contractions, but were nearly completely occluded when mean peak firing rate was increased to similar to 60 Hz. Simulated interpolated twitches did not show the marked force drop that follows the peak of the twitch, and when antidromic collisions were excluded from the model interpolated twitch amplitude was slightly increased and time-to-peak force was prolonged. These findings suggest that both antidromic and reflex effects reduce the amplitude of the interpolated twitch and contribute to the force drop that follows the twitch. The amplitude of the interpolated twitch was related to "excitation" of the motoneuron pool in a nonlinear way, so that at near-maximal contraction intensities (>90% maximal voluntary force) increases in excitation produced only small changes in interpolated twitch amplitude. Thus twitch interpolation may not provide a sensitive measure of motoneuronal excitation at near-maximal forces. Increases in the amplitude of interpolated twitches such as have been observed in fatigue and various pathologies may reflect large reductions in excitation of the motoneuron pool.