**3.1. Surface electromyography**

Surface Electromyography is a non invasive technique for measuring muscle electrical activity that occurs during muscle contraction and relaxation cycles. EMG is unique in revealing what a muscle actually does at any moment during movement and postures. Moreover, it reveals objectively the fine interplay or coordination of muscles: this is patently impossible by any other means [40].

Surface EMG is widely used in many applications, such as:

Medical

in speed. Subsequent treatments of data are increasingly complex, with the application of spectral analysis techniques to tease out underlying trends or collective patterns in the data. In this way, EMG data are making a full contribution to the comparatively new approaches

A key ingredient of strengthening protocols is *training intensity*, defined as the percentage of maximal voluntary force exerted [35]. EMG is commonly used to measure the level of muscle activation and provides a rough estimate of exercise intensity for specific muscles involved in the movement [36,35]. EMG signal has many contributions for finding the human body muscle functions [37]. EMG is the recording of the electrical activity of muscles, and therefore constitutes an extension of the physical exploration and testing of the integrity of the motor

Electromyographic analysis can provide information as to the relative amount of muscular activity an exercise requires, as well as the optimal positioning for the exercise [39]. Electro‐ physiological techniques enable us to relatively easily obtain very valuable information about neuromuscular activity [40]. Two techniques are usually used in clinical situations: neurogra‐ phy and needle EMG. The former allows the study of the response potential of a sensory, motor or mixed nerve branch subjected to an electrical stimulus applied to the surface. The latter allows the direct and precise recording of the electrical activity of the muscle being studied, both in repose and in attempts at maximum contraction [41]. Another technique that deter‐ mines the electrical activity of muscles is surface EMG. There are advantages and different application areas of sEMG in researches and in clinical practices [42,41]. In the study of muscle physiology, neural control of excitable muscle fibers is explained on the basis of the action potential mechanism. The electrical model for the motor action potential reveals how EMG signals provide us with a quantitative, reliable, and objective means of accessing muscular information [41,42,43]. When an alpha motoneuron cell is activated, the conduction of this excitation travels along the motor nerve's axon and neurotransmitters are released at the motor endplates. An endplate potential is formed at the muscle fibers and innervates the motor unit. Muscle fibres are composed of muscle cells that are in constant ionic equilibrium and also ionic flux. The semi-permeable membrane of each muscle cell forms a physical barrier between intracellular (typically negatively charged compared to external surface) and extracellular fluids, over which an ionic equilibrium is maintained [41,42,43]. These ionic equilibriums form a resting potential at the muscle fiber membrane (sarcolemma), typically -80 to -90mV (when not contracted). These potential differences are maintained by physiological processes found within the cell membrane and are called ion pumps. Ion pumps passively and actively regulate the flow of ions within the cell membrane [41,42,43]. When muscle fibers become innervated, the diffusion characteristics on the muscle fibre membrane are briefly modified, and Na+ flows into muscle cell membranes resulting in depolarization. Active ion pumps in the muscle cells immediately restore the ionic equilibrium through the repolarization process which lasts typically 2-3ms [41,42,43]. When a certain threshold level is exceeded by the influx of Na+ resulting in a depolarization of the cellular membrane, an action potential is developed and is characterized by a quick change from -80mV to +30mV. This monopolar electrical burst is restored in the repolarization phase and is followed by a hyperpolarization period. Beginning

within motor control, such as dynamical systems [33].

180 Electrodiagnosis in New Frontiers of Clinical Research

system [38].


Rehabilitation


## Ergonomics

