Force-EMG changes during sustained contractions of a human upper airway muscle.
Force-EMG changes during sustained contractions of a human upper airway muscle.
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DOI：
10.1152/jn.90922.2008
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发表时间：
2009-02
影响因子：
2.5
通讯作者：
Kori Schmitt;C. Dellorusso;R. Fregosi
中科院分区：
文献类型：
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作者：
Kori Schmitt;C. Dellorusso;R. Fregosi
人类的上呼吸道和面部肌肉支持呼吸、吞咽、言语、咀嚼和面部表情，但对它们在持续收缩中的耐力表现知之甚少。在持续收缩期间，通常与任务失败相关的肌肉疲劳具有中枢和肌内原因，每种原因的贡献被认为是任务依赖性的。以前，我们未能显示中枢疲劳的鼻扩张肌进行间歇性最大随意收缩（MVC）。在这里，我们测试的假设，中枢机制有助于疲劳的次最大，持续收缩的鼻扩张肌。在11名受试者中记录鼻扩张器肌力和EMG活动，这些受试者进行次最大收缩（20、35和65%MVC），直到力下降到或=3 s，我们将其定义为任务失败。MVC和抽搐力（后者通过对面神经施加超大冲击获得）在试验前和恢复的前10分钟内的几个时间点记录。任务失败的时间与收缩强度呈负相关。在所有三次试验中，MVC力在任务失败时大约下降了30%，但在2分钟内恢复。抽搐力下降了30-44%，这取决于收缩强度，并在恢复10分钟后保持抑郁状态，与低频疲劳一致。平均肌电图活动随时间增加，但从未超过75%的最大，试验前的水平，尽管任务失败。在所有试验中，EMG平均功率频率下降20-25%，表明任务失败时动作电位传导速度降低。与此相反，最大诱发电位没有显着变化的任何任务，表明在任务失败的EMG赤字主要是由于近端的神经肌肉接头的机制。使用内插抽搐技术的其他实验表明，受试者可以用这块肌肉产生约92%的最大唤起力，这并不是一个足够大的缺陷来解释任务失败时EMG的整个不足。这些数据表明，神经系统未能充分激活鼻扩张肌在持续的，次最大的收缩，假定的机制进行了讨论。
Human upper airway and facial muscles support breathing, swallowing, speech, mastication, and facial expression, but their endurance performance in sustained contractions is poorly understood. The muscular fatigue typically associated with task failure during sustained contractions has both central and intramuscular causes, with the contribution of each believed to be task dependent. Previously we failed to show central fatigue in the nasal dilator muscles of subjects that performed intermittent maximal voluntary contractions (MVCs). Here we test the hypothesis that central mechanisms contribute to the fatigue of submaximal, sustained contractions in nasal dilator muscles. Nasal dilator muscle force and EMG activities were recorded in 11 subjects that performed submaximal contractions (20, 35, and 65% MVC) until force dropped to or=3 s, which we defined as task failure. MVC and twitch forces (the latter obtained by applying supramaximal shocks to the facial nerve) were recorded before the trial and at several time points over the first 10 min of recovery. The time to task failure was inversely related to contraction intensity. MVC force was depressed by roughly 30% at task failure in all three trials, but recovered within 2 min. Twitch force fell by 30-44% depending on contraction intensity and remained depressed after 10 min of recovery, consistent with low-frequency fatigue. Average EMG activity increased with time, but never exceeded 75% of the maximal, pretrial level despite task failure. EMG mean power frequency declined by 20-25% in all trials, suggesting reduced action potential conduction velocity at task failure. In contrast, the maximal evoked potential did not change significantly in any of the tasks, indicating that the EMG deficit at task failure was due largely to mechanisms proximal to the neuromuscular junction. Additional experiments using the interpolated twitch technique suggest that subjects can produce about 92% of the maximal evocable force with this muscle, which is not a large enough deficit to explain the entire shortfall in the EMG at task failure. These data show that the nervous system fails to fully activate the nasal dilator muscles during sustained, submaximal contractions; putative mechanisms are discussed.