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

肌肉可能包含数十万个单独的肌肉纤维。这些纤维被分成功能单元（10 - 1000个纤维），由单个运动神经元激活。单个运动神经元和它所激活的所有肌肉纤维称为运动单元（MU）。一个MU的激活会导致它的肌肉纤维一致收缩和放松（或“抽搐”），产生一个单位的力。******可以通过招募额外的MU（招募）或增加每个MU每秒被激活的次数（速率编码）来增加力。更频繁地激活mu可以使抽动力在更大程度上及时重叠，并更有效地总结。当肌肉开始收缩时，有时在连续的MU放电之间有一段不寻常的短脉冲间隔（双脉冲）。抽搐力的总和也会受到肌肉周围状况的影响。中度到强烈的收缩可以激活肌肉蛋白内的生化过程，增强MU的抽搐力，用于随后的收缩，称为活化后增强（PAP）。在PAP存在时，神经系统降低了MU放电率，以适应更大的抽搐力。****** PAP和MU放电之间的相互作用可能由肌肉长度介导。关节角度可以通过改变其长度来增加或减少肌肉-肌腱单元（MTU）内的顺应性。在较短的肌肉长度，当顺应性较大时，抽搐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。肌肉长度越长，情况就越复杂。在较长的肌肉长度时，遵从性在MTU内降低，这对于时间求和是最佳的。然而，对肌肉的电刺激表明，PAP仍然可以在较长的肌肉长度中存在，并干扰时间累加。因此，PAP有可能在任意肌肉长度的随意控制中影响MU活动模式。我们试图了解疲劳收缩期间肌肉的神经控制也受到PAP和MU活动之间关系的影响。在PAP存在时观察到的MU放电率的下降也类似于MU同步，其中MU同时被招募以叠加它们的抽搐力。结果类似于单个增强的MU抽搐。当从皮肤表面测量肌肉电活动时，PAP和MU同步可以产生类似于另一种潜在机制的肌肉电信号变化：更多MU的逐渐招募，然后当它们疲劳时，它们只是停止放电。本提案概述了一种分层的方法，通过每个连续的研究来解开在非疲劳和疲劳收缩中调节力的中枢和外围因素，以理解对肌肉的运动命令。

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.