**3. Electromyography**

Electromyography is the electrodiagnostic study of muscles and nerves. The test includes two components: Nerve conduction studies (NCS) and electromyogram (EMG). Nerve conduction studies measure how well and how fast the nerves can send electrical signals [30]. NCS can be defined as the recording of a peripheral neural impulse at some location distant from the site where a propagating action potential is induced in a peripheral nerve [2]. Nerve conduction

studies provide unique quantitative information about neurological function in patients with a variety of neuromuscular disorders [31]. A nerve is stimulated at one or more sites along its course and the electrical response of the nerve is recorded. EMG testing involves evaluation of the electrical activity of a muscle and is one of the fundamental parts of the electrodiagnostic medical consultation. It is both an art and a science. It requires a thorough knowledge of the anatomy of the muscles being tested, machine settings and the neurophysiology behind the testing [2]. Obtaining the information produced by active muscle provides information about the activities of motor control centers [30,26]. This can be achieved invasively, by wires or needles inserted directly into the muscles, or noninvasively, by recording electrodes placed over the skin surface overlying the investigated muscles. The use of this latter modality is preferable in healthy voluntary sedentary subjects and in athletes, despite its limitations and drawbacks. To mention just a few of them, single-channel sEMG signals provide average information on the activity of many concurrently active motor units, the reproducibility of the results is often difficult, and standard recording procedures are still confined to few labora‐ tories, therefore limiting comparisons among results obtained by clinical researchers [26]. EMG signal recordings used for years in bio-engineering, occupational- and sports medicine, physiotherapy, sports biomechanics, and also eventually for trainers and coaches [19,32]. Since the end of the 1960s there has been a development in miniaturized telemetric devices for monitoring complex human movements remotely. Especially for kinesiological purposes, the telemetric devices have recently been changed from two-channel registrations to eight or morechannel systems [32]. EMG is a seductive muse because it provides easy access to physiological processes that cause the muscle to generate force, produce movement, and accomplish the countless functions that allow us to interact with the world around us. The current state of surface EMG is enigmatic. It provides many important and useful applications, but it has many limitations that must be understood, considered, and eventually removed so that the discipline is more scientifically based and less reliant on the art of use. To its detriment, EMG is too easy to use and consequently too easy to abuse [5]. Electromyographic recordings are performed with intramuscular needle electrodes. However, surface electrodes are used in the study of sports science. Most of the issues affecting this modality have already been covered. Electrodes are almost always sited along the body of the muscle in question, with locations one-third and two-thirds along the length being the norm, As mentioned earlier, small pre-amplifiers are often used in order to improve signal-to-noise ratios, especially since telemetry of signals is increasingly used in order to maintain ecologically valid movement patterns [30,33,1,34]. Once the signal is filtered and amplified, some form of rectification of the signal is usually applied. As with other indices, examination of the raw signal waveform is interesting but offers little in the way of empirically analyzable data. Accordingly, and since the signal is made up of both positive and negative potentials, signals may be rectified by either ignoring all negative signals or reversing their polarity so that all signals are positive. Further signal conditioning may involve totaling activity across a regular time base, resetting counters to zero in order to provide an integrated signal. Analysis may look at amplitude or, more rarely, frequency. Increasingly, however, signal patterns are compared across two or more conditions. Thus, investigators may contrast "at rest" with active patterns, or use an increase from baseline measure, or contrast signals obtained under different execution conditions such as variations

an attempt to lift an immovable object or an object that is too heavy to move. The muscle fibers contract in an attempt to move the weight, but the muscle does not shorten in overall length because the object is too heavy to move [28,23,29]. Concentric muscle action occurs when the muscle force exceeds the external resistance, resulting in joint movement as the muscle shortens. Concentric action occurs when a muscle is active and shortening; for example, during the biceps curl the biceps shortens and exerts enough force to lift the barbell [23,29]. Eccentric muscle action occurs when the external resistance exceeds the force supplied by the muscle, resulting in joint movement as the muscle lengthens; for example, when lowering the barbell the biceps exerts force to ensure the movement is controlled. This is often referred to as the negative portion of the repetition. Even though the fibers are lengthening, they are also in a state of contraction, permitting the weight to return to the starting position in a controlled manner. During an eccentric action, an activated muscle is forced to elongate while producing

**Figure 1.** When a skeletal muscle fiber is activated by a MUAP, a wave of electrical depolarization travels along the

Electromyography is the electrodiagnostic study of muscles and nerves. The test includes two components: Nerve conduction studies (NCS) and electromyogram (EMG). Nerve conduction studies measure how well and how fast the nerves can send electrical signals [30]. NCS can be defined as the recording of a peripheral neural impulse at some location distant from the site where a propagating action potential is induced in a peripheral nerve [2]. Nerve conduction

tension [27,23,29].

**3. Electromyography**

surface of the fiber (drawn by Sözen H.).

178 Electrodiagnosis in New Frontiers of Clinical Research

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

from the motor end plates, the action potential spreads across the muscle fibers in both directions at a propagation speed of 2-6m/s. The action potential leads to a release of calcium ions in the intracellular fluid and produces a chemical response resulting in a shortening of the contractile elements of muscle cells [41,42,43]. The depolarization-repolarization process described is a monopolar action potential that travels across the surface of the muscle fiber [41,42,43]. Electrodes in contact with this wave front present a bipolar signal to the EMG differential amplifiers because the electrodes are measuring the difference between two points along the direction of propagation of the wave front. EMG signals provide us with a viewing window into the electrical signals presented by multiple muscle fibres and are in fact a

Surface Electromyography in Sports and Exercise

http://dx.doi.org/10.5772/56167

181

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

superposition of multiple action potentials [43].

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

**3.1. Surface electromyography**

other means [40].

Medical

**•** Orthopedic

**•** Functional Neurology

**•** Psychophysiology

**•** Post surgery/accident

**•** Physical Rehabilitation

**•** Active Training Therapy

**•** Analysis of demand

**•** Risk Prevention

**•** Physical Therapy

**•** Neurological Rehabilitation

Rehabilitation

Ergonomics

**•** Gait & Posture Analysis

**•** Urology (treatment of incontinence)

**•** Surgery

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 system [38].

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 from the motor end plates, the action potential spreads across the muscle fibers in both directions at a propagation speed of 2-6m/s. The action potential leads to a release of calcium ions in the intracellular fluid and produces a chemical response resulting in a shortening of the contractile elements of muscle cells [41,42,43]. The depolarization-repolarization process described is a monopolar action potential that travels across the surface of the muscle fiber [41,42,43]. Electrodes in contact with this wave front present a bipolar signal to the EMG differential amplifiers because the electrodes are measuring the difference between two points along the direction of propagation of the wave front. EMG signals provide us with a viewing window into the electrical signals presented by multiple muscle fibres and are in fact a superposition of multiple action potentials [43].
