**1. Introduction**

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Exercise is constantly gaining popularity. It has been widely used especially in the fields of sports performance and rehabilitation [1].

Performance and ability tests enable the success in education of sports and exercise. Various exercise equipments are used in test protocols that are developed for this goal. The reason to use various kinds of exercise equipments for performance measurement is that every equip‐ ment and protocol cause different responses in human body. The cause for evolution of different physiological responses is about the different shapes and densities of different muscles. In this very respect, the electromyographic measurements gain great importance.

Electromyographic studies help us understand the location of the problem in the system of movement. The problem may be localized to the peripheral nervous system or the muscle itself and sometimes may also be at the neuromuscular juntion. This diagnostic tool is therefore very valuable in the differential diagnosis of nerve and muscle diseases [2]. Electromyography is also used in morphological analysis of the motor unit [3. It is important to snychronize the systems that supply cinematic data with electromyography to determine the period when different muscles join the muscle movement. These systems use cameras, electrogoniometers and other registration tools with their programs in order to give us information about position, speed and acceleration measurements. Additionaly, the study can be completed with podom‐ eter and power platform as power analysis systems and this is called the kinetic system. Surface EMG (sEMG) is an important tool of biomechanical analysis and a very important part of this system. [4,5]. It helps to understand the role of a muscle in a spesific movement [6,7]

Surface EMG has increasing importance in sports and occupational medicine and in ergonomic studies [8,9]. It can also establish dynamic analysis and therefore is important in sports [10,11]. The utilization of muscles in a right and economical fashion helps improve activity and prevents the risk of injury. The most important points to achieve healthy training are the follow

up of development and performing corrections where necessary [5,12,13]. The electromyo‐ graphical analysis can determine muscle activation and fatigue and thus helps achieve development of performance [9].

heat to help maintain body temperature [17]. Skeletal muscle converts chemical energy to mechanical and heat energy. Skeletal muscle uses adenosine triphosphate (ATP) as fuel during electrical, mechanical and chemical events. This process, called action potential begins with an electrical impulse from the brain [22,23]. This initiates a chain of biochemical reactions that ends in the burning of adenosine triphosphate, the fuel for muscle contraction. Its use results in the forces that move the limbs and generate heat. Electrodes attached to a muscle group record the electrical activity accompanying contraction; the name of this recording process is

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Motor units are the functional assets of the neuromuscular system. Each motor unit consists of a single motoneuron and the muscle fibers supplied by its axonal branches [24,25]. Once a motoneuron discharges, action potentials are generated at its neuromuscular junctions and then propagate along all the muscle fibers, toward the tendon regions. The summation of these potentials is termed motor unit action potentials and is responsible for the muscle contraction [25]. MUAP is the sum of the extracellular potentials of muscle fiber action potentials of a motor unit [3]. The waveform is determined by the natural properties of the relationship between muscle fibers. [24,3]. The extracellularly recorded MUAP, recorded along the length of the muscle fibers and away from the endplate region, has a triphasic waveform. The initial positive deflection represents the action potential propagating towards the electrode. As the potential passes in front of the electrode the main positive-negative deflection is recorded. When the action potential propagates away from the electrode the potential returns to the baseline. Slight repositioning of the electrode causes major changes in the electrical profile of the same motor unit. Therefore, one motor unit can give rise to MUAPs of different morphology at different recording sites. If the electrode is placed immediately over the endplate area, the initial positive deflection will not be recorded and the potential will have a biphasic waveform with an initial negative deflection [3]. All the muscle fibers of a motor unit work in unison; that is, all are discharged nearly synchronously upon the arrival of a nerve impulse along the axon and through its terminal branches to the motor end plates. A MUAP is recorded by a needle electrode. The recorded motor unit action potential can be derived from action potentials of a small number of muscle fibers, a moderate number of muscle fibers, or a great majority of

Among the variety of types of muscle action are the isometric, concentric and eccentric; all three forms occur during the actions seen in sport and exercise performance [27]. When there is no change in muscle length during muscle activation, the action is called isometric. Isometric action occurs when an athlete tries to leg-press a heavy load by flexing the quadriceps muscles, but cannot move the weight-stack in spite of a maximum effort. The muscle produces force, but it is insufficient to overcome the mass of the weight stack; hence, the overall muscle length does not shorten. Isometric muscle action occurs when the muscle contracts without moving, generating force while its length remains static. Isometric muscle actions are demonstrated in

electromyography (EMG) [23].

**2.2. The Motor Unit Action Potential (MUAP)**

muscle fibers belonging to the motor unit [26].

**2.3. Types of muscle action**

Muscle activation is a result of the effort of muscle but the relationship between EMG activity and effort is only qualitative [5].

Surface EMG in current sports studies also deals with determination and descriptions of the muscle types [14,15].
