Failure of activation of spinal motoneurones after muscle fatigue in healthy subjects studied by transcranial magnetic stimulation
Failure of activation of spinal motoneurones after muscle fatigue in healthy subjects studied by transcranial magnetic stimulation
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DOI：
10.1113/jphysiol.2003.043562
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发表时间：
2003-08-15
影响因子：
5.5
通讯作者：
Krarup, C
中科院分区：
文献类型：
--
作者：
Andersen, B;Westlund, B;Krarup, C
在持续的最大努力过程中，驱动运动神经元（MN）的能力逐渐下降。我们使用最近开发的三重刺激技术（TST）研究健康受试者疲劳运动后的皮质脊髓传导。该方法采用碰撞技术来估计由经颅磁刺激激活的运动单位的比例。在小指展肌以50%最大力持续收缩至力竭后，TST反应立即从> 95%降低至约60%。这种效应在1分钟内恢复到对照水平，意味着脊髓MN数量减少。额外的TST实验后，最大和次最大的努力表明，TST反应的大小的减少与运动的持续时间和强度。运动诱发电位（MEP）后，传统的经颅磁刺激（TMS）和周围神经刺激的反应记录后，相同的疲劳协议。收缩后MEP和外周反应的大小增加，与TST反应大小的减少形成直接对比。这表明疲劳期间重复脊髓MN激活的可能性增加，即使池中的一些MN未能放电。静息期持续时间皮层刺激后延长了平均55 ms的收缩后，并恢复在一个时间过程中类似的TST反应抑郁症。总体而言，结果表明，从运动皮层流出可能变得不足以驱动所有的脊髓MN放电时，肌肉疲劳和激活失败和补偿机制之间的复杂的相互作用，以维持运动单位激活发生在持续的自愿活动。当在次最大努力期间无法维持力量时，运动单位的激活失败是主要的。
During a sustained maximal effort a progressive decline in the ability to drive motoneurones (MNs) develops. We used the recently developed triple stimulation technique (TST) to study corticospinal conduction after fatiguing exercise in healthy subjects. This method employs a collision technique to estimate the proportion of motor units activated by a transcranial magnetic stimulus. Following a sustained contraction of the abductor digiti minimi muscle at 50 % maximal force maintained to exhaustion there was an immediate reduction of the TST response from > 95 % to about 60 %. This effect recovered to control levels within 1 min and implies that a decreased number of spinal MNs were excited. Additional TST experiments after maximal and submaximal efforts showed that the decrease in size of the TST response was related to duration and strength of exercise. Motor evoked potentials (MEPs) after conventional transcranial magnetic stimulation (TMS) and responses to peripheral nerve stimulation were recorded following the same fatigue protocol. The size of both the MEPs and the peripheral responses increased after the contraction and were in direct contrast to the decrease in size of the TST response. This points to increased probability of repetitive spinal MN activation during fatigue even if some MNs in the pool failed to discharge. Silent period duration following cortical stimulation lengthened by an average of 55 ms after the contraction and recovered within a time course similar to that of the TST response depression. Overall, the results suggest that the outflow from the motor cortex could become insufficient to drive all spinal MNs to discharge when the muscle is fatigued and that complex interactions between failure of activation and compensatory mechanisms to maintain motor unit activation occur during sustained voluntary activity. When inability to maintain force occurs during submaximal effort, failure of activation of motor units is predominant.