## 1 Introduction  
The center of pressure (COP) index is used in research as a way to measure equilibrium and posture because it depends on the position of the body to the support surface [1, 2, 3, 4, 5]. Any movement of the body that causes changes in the values of the forces acting on the ground in the anteroposterior (AP) and mediolateral (ML) directions can affect the point of application of the resultant force. The COP indicator contains a great deal of information about the manifestations of the regulatory function of the equilibrium system. It is commonly used in measurements to assess the stability and quality of this system and to evaluate postural strategies [1, 2, 3, 4, 5, 6]. Based on the measurement of the COP displacement along the so-called sway path length, the degree of postural sway by the test subject can be quantified and can serve as an indirect measurement of equilibrium control. The amount and distribution of pressure can also be recorded; it provides additional information on the structure and function of the sole [7]. COP variables are the range of sway in the AP and ML directions [8]. This swaying is caused by slight muscle contractions to maintain equilibrium while standing. Increased sway is not necessarily an indicator of poorer equilibrium, but it is an indicator of reduced neuromuscular control [9; 10; 11]. According to [PERSON], [PERSON], and [PERSON], the neuromuscular system must exert 50% more effort to control stability toward the sagittal plane (AP) to maintain a stable posture [12]. It is essential to comprehensively and objectively evaluate the equilibrium system of athletes to assess their stability. Even when standing quietly, a certain amount of body deviation from vertical is observed, and this postural sway is considered an indicator of the efficiency of the equilibrium control system [4]. When the disturbance is minimal, the peroneus muscles and the flexors and extensors of the foot are the main muscle groups responsible for stabilizing the ankle joint (known as the ankle joint strategy). Adjustment at the hip level becomes more important for more severe disorders (hip strategy), involving the restoration of the center of gravity through significant movements at the hip joints [13; 14; 15]. Studying postural stability in sports can provide insight into the development of specific postural strategies [16]. According to [PERSON] et al., training allows athletes to acquire new equilibrium control skills, which vary depending on the sport practiced [17]. The severity of sway in the standing position can be assessed by measuring the COP motion parameters of the feet that are recorded by a computerized equilibrium platform [4]. The choice of method for assessing postural stability is motivated by factors such as reliability, so that noticeable differences in measurements are due to real variability in postural adaptation and not to random errors in the testing procedure [18; 19]. Nowadays, commonly used tools for assessing static and dynamic body equilibrium include baropodometric platforms. Changes in the displacement direction of the COP exerted by the feet on the surface of the platform are recorded while taking measurements in the standing position. The signal that characterizes COP displacement under static conditions is the projection of the body's overall center of gravity onto the support plane. The results of the measurements allow us to assess the functioning of the postural stability control system [12]. This control is not considered a simple sum of static reflexes, but rather a complex skill based on the interaction of dynamic sensory processes. The two main functional goals of postural behavior are postural orientation and postural equilibrium [12; 20; 21]. Several years of training can significantly affect the postural control system and lead to discipline-oriented optimal use of the sensorimotor modalities responsible for body equilibrium [22]. It is a key component of motor skills, as well as maintaining a stable posture and performing complex sports skills [23].