Estimation of the muscle fibre semi-length under varying joint positions on the basis of non-invasively extracted motor unit action potentials

Monopolar surface electromyography: a better tool to assess motoneuron excitability upon passive muscle stretching

“…This becomes particularly important when the motor units are being voluntary activated because of the nature of their un-synchronized firing [27]. In addition, in this study, there were no significant differences in the onset latency and the inter-peak time interval of the monopolar signal at all testing conditions.…”

Triceps surae stretch and voluntary contraction alters maximal M-wave magnitude

“…Subsequently, changes in the recording electrode to the test muscles active muscle fibres are expected throughout an investigation (discussed in [32]). The movement of the electrodes relative to underlying muscle fibres becomes particularly important in the current investigation as a result of the complex innervation zones of the human gastrocnemius and soleus muscles (reviewed in [37]) given that large differences in SEMG amplitude are noted when electrodes are placed in different locations relative to the innervation zones of muscles [25,24,30,29].…”

“…This is a result of the initiation potential, the motor-unit potential and the non-propagating potential that exists due to electro-conductance of the motor-unit potential when it reaches the muscle fibre-tendon junction [27,12,1,32], discussed in [36]. It is well understood that the summation of many triphasic motor-unit potentials, which are slightly out of phase, will result in some signal cancellation.…”

“…This type of signal cancellation is inevitable during surface recording and will result in the amplitude of both background muscle activity and the maximal Mwave (as well as any other surface recorded muscle response) being smaller than the predicted summation of all the individual motor unit potentials [21]. Cancellation of motor-unit potentials becomes particularly important when motor units are being voluntarily activated because of their un-synchronised firing nature [32]. Further to this, Gydikov and Kosarov [17] demonstrated that the onset of the motor-unit potential negative phase, and that of the positive end plate potential, varies with joint angle and therefore the length of muscle fibres.…”

From cell to movement: to what answers does EMG really contribute?

“…Furthermore, the detection of the non-travelling component of the MUP stimulates further investigation into muscle fibre properties such as, e.g. fibre length [44]. This knowledge may prove to be important especially in the field of dynamic EMG, that is EMG acquired during nonisometric and non-isotonic contractions.…”