Modifica di Electromyography (sezione)

====Localization and Positioning of Electrodes====
Electrodes should be placed between a motor point of muscle innervation and the tendon or between two motor points, and oriented along the muscle belly's longitudinal median line. Thus, the longitudinal axis of the electrodes should be aligned parallel to the length of the muscle fibers.

Electrodes should not be placed near the tendon. In such locations, muscle fibers are thin and sparse, and there is also the risk of "picking up" sEMG signals from other muscles (e.g., agonists).

Similarly, electrodes should not be placed on the motor point, although this is a difficult preconception to overcome. The motor point is the point on the muscle (and its equivalent projection on the skin) where the injection of a minimal current causes a well-defined contraction of the muscle itself. Usually, but not always, this point corresponds to the part of the muscle where innervation occurs and where the highest density of neurons is found.

However, from the standpoint of signal stability, measuring with two electrodes near the motor point is the worst situation to be in. From this region, the activation potentials of the muscle fibers propagate proximally and distally, and the relative positive and negative phases either sum or cancel out on the electrodes, producing a very distorted signal characterized by sharp, sudden spikes due to the random situation. Stability is particularly compromised here because it is evident that small movements of the electrode will cause huge variations in the trace and its frequency and phase characteristics.

It is also not advisable to place electrodes at the muscle's extremes (one on the origin and one on the insertion). In this case, too large a volume of tissue is under observation, and signals from muscles that are not of interest are easily captured.