A unified approach towards understanding the physiological significance of surface electromyographic signal

肌肉中可能含有数十万条单独的肌肉纤维。这些纤维被分成由单个运动神经元激活的功能单位(101000个纤维)。单个运动神经元及其激活的所有肌肉纤维称为运动单位(MU)。一个MU的激活会导致它的肌肉纤维收缩和松弛，产生一个单位的力量。*可以通过招募额外的MU(招募)或增加每个MU每秒激活的次数(速率编码)来增加力量。更频繁地激活MU可以使抽动力在时间上更大程度地重叠，并更有效地进行总结。当肌肉开始收缩时，有时在连续的MU发射之间有一段非常短的脉冲间间隔(双脉冲)。痉挛力量的总和也会受到肌肉外周状况的影响。中等到强烈的收缩可以激活肌肉蛋白质内的生化过程，从而增强MU的抽动力，用于随后的收缩，称为激活后增强(PAP)。在PAP存在的情况下，神经系统会降低MU的放电频率，以适应更大的抽动力。PAP和MU放电之间的相互作用可能是由肌肉长度调节的。关节角度可以通过相应地改变肌肉-肌腱单元(MTU)的长度来增加或减少其顺应性。当顺应性较大时，在较短的肌肉长度下，抽动力的时间总和效率较低。巧合的是，在这些条件下，增强是最大的。肌肉长度较长时，情况会变得复杂。在较长的肌肉长度时，MTU内的顺应性降低，这是时间总和的最佳选择。然而，对肌肉的电刺激表明，PAP仍然可以存在于较长的肌肉长度，并干扰时间总和。因此，在任意肌肉长度的自愿控制过程中，PAP有可能影响MU的活动模式。我们试图了解疲劳收缩时肌肉的神经控制也受到PAP和MU活动之间的关系的影响。在PAP存在的情况下观察到的MU放电率的下降也类似于MU同步，MU被同时招募来叠加它们的抽动力量。结果类似于一次增强的MU抽动。当从皮肤表面测量肌肉电活动时，PAP和MU同步都可以在肌肉电信号中产生类似于另一种潜在机制的变化：逐渐招募更多的MU，然后当它们疲劳时，它们干脆停止发射。这项建议概述了每个后续研究的分层方法，以分离在非疲劳和疲劳性收缩中调节力量的中央和外围因素，以了解肌肉的运动命令。

Muscles may contain several hundreds of thousands of individual muscle fibers. These fibers are grouped into functional units (10 1000 fibers) activated by a single motor neuron. A single motor neuron and all the muscle fibers that it activates is a called a motor unit (MU). Activation of one MU will cause its muscle fibers contract and relax in in unison (or, “twitch”) producing one-unit of force. ******Force can be increased by recruiting additional MUs (recruitment), or by increasing the number of times per second that each MU is activated (rate-coding). Activating MUs more frequently allows twitch-forces to overlap in time to a greater degree and sum up more efficiently. When the muscle starts contracting, sometimes there is a brief period of unusually short inter-pulse intervals between successive MU firings (doublets). The summation of twitch-forces can also be affect by peripheral conditions in the muscle. A moderate to intense contraction can activate biochemical processes within the muscle proteins that augment MU twitch-forces, for the subsequent contraction, termed post-activation potentiation (PAP). The nervous system decreases MU firing rates in the presence of PAP, to accommodate the larger twitch-forces.******The interaction between PAP and MU firing may be mediated by muscle length. Joint angle can increase or decrease compliance within the muscle-tendon unit (MTU) by changing its length, accordingly. Temporal summation of twitch-forces is less efficient at shorter muscle lengths when the compliance is greater. Potentiation is, by coincidence, greatest under these conditions. The situation is complicated at longer muscle lengths. Compliance decreases within the MTU at longer muscle lengths, which is optimal for temporal summation. However, electrical stimulation of the muscle has shown that PAP can still be present at longer muscle lengths and interfere with temporal summation. Thus, there is the possibility that PAP can affect MU activity patterns during voluntary control at any muscle length. Our attempts to understand the neural control of muscle during fatiguing contractions is also affected by the relationship between PAP and MU activity. The decrease in MU firing rates observed in the presence of PAP also resembles MU synchronization, where MUs are recruited simultaneously to superimpose their twitch forces. The result resembles a single potentiated MU twitch. When muscle electrical activity is measured from the skin surface, both PAP and MU synchronization can produce changes in the muscle electrical signals that resemble another potential mechanism: the progressive recruitment of more MUs, then as they fatigue, they simply stop firing. This proposal outlines a layered approach with each successive study to disentangle central and peripheral factors that regulate force in non-fatiguing and fatiguing contractions, to understand motor commands to the muscle.