| Term | Definition |
|---|
| Alpha-motoneuron | the neural structure whose cell body is located in the anterior horn of the spinal cord and which, through its relatively large diameter axon and terminal branches, innervates a group of muscle fibers. |
| Motor unit (MU) | the term used to describe the single smallest controllable muscular unit, consisting of a single alpha-motoneuron, its neuromuscular junction, and the muscle fibers it innervates (as few as 3, as many as 2000). |
| Muscle fiber action potential (MAP) | the name given to the detected waveform resulting from the depolarization wave as it propagates in both directions along each muscle fiber from its motor end plate. |
| Motor unit action potential (MUAP) | the name given to the detected waveform consisting of the spatiotemporal summation of individual muscle fiber action potentials originating from muscl fibers in the vicinity of a given electrode or electrode pair. |
| Motor unit action potential train (MUAPT) | the name given to a repetitive sequence of MUAPs from a given motor unit. |
| Interpulse interval (IPI) | the time between adjacent discharges of a motor unit, it is a semirandom quantity. |
| Instantaneous firing rate | the parameter which represents the inverse value of the interpulse interval. |
| Average firing rate | the average firing rate of a motor unit over a given period of time, it is measured in units of pulses per second. |
| Synchronization | the term which describes the tendency for a motor unit to discharge at or near the time that another motor unit discharges. It therefore describes the interdependence or entrainment of two or more motor units. |
| Electromyographic (EMG) signal | the name given to the total signal detected by an electrode. It is the algebraic summation of all MUAPTs from all active motor units within the pick-up area of the electrode. |
| Myoelectric signal | an alternative nomenclature for the electromyographic signal. |
| Amplitude | the quantity which expresses the level of the signal activity. |
| Time duration | the amount of time over which a waveform presents detecable energy. |
| Phase | in electromyography, the net excursion of the amplitude of a signal in either the positive or negative direction. |
| Shape | the characteristic of a signal which remains unaltered with linear scaling in either the amplitude or time domains. An example of such characteristics are the phases of an action potential. |
| Waveform | the term which describes all aspects of the excursion of the potential, voltage, or current associated with a signal as a function of time. It incorporates all the notions of shape, amplitude, and time duration. |
| Decomposition | the process whereby individual MUAPs are extracted from the electromyographic signal. |
| Electrode | a device or unit through which an electrical current enters or leaves an electrolyte, gas, or vacuums. |
| Detection surface | the portion of the electrode which is in direct contact with the medium which is being sensed. |
| Unipolar electrode | one which consists of one detection surface. |
| Bipolar electrode | one which consists of two detection surfaces. |
| Concentric electrode | a unipolar electrode in which the detection surface is located in the center of a metallic shield (typically, the cannula of a needle), which in turn is connected to ground. |
| Detection | the process of sensing the signal by the electrode. |
| Recording | the process which creates a record of the detected signal on any media (CRT, paper, magnetic tape, etc.) |
| Isometric contraction | one during which the length of the contracting muscle remains constant. Generally, the muscle length is assessed by monitoring the angle of the joint being affected. |
| Anisometric contraction | one during which the length of the contracting muscle may vary. |
| Ballistic contraction | one that is executed with the greatest speed physiologically possible. |
| Maximal voluntary contraction (MVC) | the greatest amount of effort that an individual may exert. Usually, the effort is concentrated on one muscle or on one joint. It is generally measured by monitoring the force or torque output. |
| Agonist muscle | one which initiates a contraction. |
| Antagonist muscle | one which actively provides a negative contribution to a particular function during a contraction. |
| Synergist muscle | one which actively provides an additive contribution to a particular function during a contraction. |
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