**4. Type and placement of electrodes**

The electrodes available for kinesiological EMG are the passive and active surface type and the intramuscular type, each with its distinct characteristics, recommendations for use, advantages and disadvantages. The choice of electrode for capturing the EMG signal depends on the characteristics of the evaluated muscles. Thus, when analyzing certain muscles, size and location should be considered in the selection and application of electrodes [27].

Application of Surface Electromyography in the Dynamics of Human Movement 397

**Figure 2.** Diagram representing the placement of surface electrodes the direction of muscle fibers [3].

EMG is a generic term for a method of recording the electrical activity of a muscle contraction. The numerous applications of electromyography (EMG) include diagnosing neuromuscular disease and determining the presence of dysfunctions or abnormalities in clinical practice, the rehabilitation of muscle action via EMG biofeedback, demonstrating kinesiology in anatomical studies, use in ergonomics as a tool for studying kinesiological muscle function related to posture and other biomechanical stress indicators, as well as a movement pattern identifier and a nervous system control parameter of the nervous system

When interpreting the EMG signal for quantitative analysis, three fundamental characteristics can be distinguished: duration, amplitude and frequency, each of which is

The duration of EMG activity corresponds to the activation time of the selected muscle. The amplitude expresses the level of signal activity and varies with the amount of electrical activity detected in the muscle. It provides information on the intensity of muscle activation. RMS, average value, peak value and peak-to-peak value are ways of evaluating the amplitude of the signal. The frequency can be understood as the rate of excitation of the muscle cell. The frequency distribution of the EMG signal is due to a wide range of factors: muscle composition, the characteristics of the action potential of the active muscle fibers, the intramuscular coordination processes, the properties of the

It can be said that signal processing begins, indirectly, as soon as the electrodes are placed. Electrode placement involves several factors that are decisive for the level and purity of the EMG signal to be collected, including: cleaning the skin, the amount and temperature of the conductive gel, the position of the electrodes and the signal-to-noise ratio, which expresses the balance between the energy of the signal generated during muscle contraction and the

The EMG signals are affected by anatomical and physiological muscle properties, peripheral nervous system control and the instrumentation used to collect the signal. Thus it is important to understand the basic muscle functions to correctly record EMG

**4.1. Considerations on the acquisition of EMG signals** 

[28].

briefly described below [12].

electrodes and their placement.

signals [12].

energy of noise from various undesirable sources [27].

The placement of surface electrodes is also another factor that influences the reliability of EMG recordings. The size, orientation and topography of electrodes influence EMG recordings [25].

Since the amplitude of the electrical potential is derived from the difference in potential observed between the electrodes, the inter-electrode distance should be controlled. Due to changes in distance, the same levels of contraction can result in different EMG signal amplitudes [24]. A major concern in sEMG is signal interference (cross-talk) from muscles surrounding the electrode. In one study [12], the surface electrodes were positioned on the midline of the muscle venter between the motor and the myotendonous junction with the detection surface towards the oriented fibers. However, this study was limited in that the electrodes were positioned between the motor and the myotendonous junction without electrically stimulating the motor points.

The surface area and shape of the electrode's contact surface as well as its location affect the signal amplitude, and the distance between the contact surfaces of the electrode affects the signal frequency. Figure 1 shows the characteristics of the EMG signal relative to the electrode position over the fibers. The most suitable location for electrode placement is in the direction of muscle fibers (Figure 2) and near the point of greatest electrical activity.

**Figure 1.** Representative signal results from different points in the muscle [3].

The electrodes must be carefully placed with regard to the adjacent muscles, since if the electrodes are too close to the other muscles then cross-talk may occur. Another important factor is the placement of the ground or reference electrode, which must have a good contact area.

**Figure 2.** Diagram representing the placement of surface electrodes the direction of muscle fibers [3].
