## 1 Introduction
The fundamental difference between these two techniques is the direction of the strike. In a turning kick, the foot moves in an arc along the body's axis, while in a side kick, the foot is moved sideways towards the opponent [21; 22]. Determining the effective mass in these strikes is important for training practice and preparation for combat. Effective mass, a term often used interchangeably with \"inertial mass,\" refers to the portion of an athlete's body mass that effectively contributes to the force of a strike. This mass is not a static measure, but is dynamically influenced by several biomechanical factors, including muscle stiffness, co-contraction, and the kinetic chain involved in the movement. A critical aspect of effective mass is its dependence on the biomechanical alignment and muscular activation at the moment of impact. When a fighter executes a strike, not all body mass contributes equally to the impact. The effective mass is predominantly determined by the mass of the body segments in motion and their velocity, but, significantly, it is also influenced by the stiffness of the muscles and joints involved [23]. Muscles that are actively contracted at the moment of impact can increase the effective mass of the striking limb, thereby enhancing the force delivered [8]. Furthermore, the concept of joint stiffness is integral to understanding effective mass. Increased joint stiffness through muscle co-contraction can lead to a higher transfer of force. This biomechanical strategy is often observed in skilled fighters, who can adeptly modulate their joint stiffness to maximize the impact force. It is not only about the mass, but about how effectively this mass is used in the context of a combat sport movement. The kinetic chain, which refers to the sequence of movements in different body parts leading up to a strike, also plays a critical role in the effective mass. Efficient kinetic chain sequencing can augment the effective mass involved in a strike. For instance, a punch that properly harnesses the sequential movement from the legs through the torso to the arm and fist can deliver a more potent force than a punch that relies solely on the arm's movement. The dynamics equations used to determine effective mass in combat sports [9; 23; 24] are based on simple models of the principle of conservation of momentum. Measurements of effective mass and estimates calculated from regression equations [25] confirm that the studied athletes presented higher effective masses than their estimated hand masses, confirming what has been suggested by other researchers [16]. Moreover, with such a measurement, effective mass can vary depending on the mass of the object being struck. Investigating momentum transfer in combat sports uncovers critical biomechanical dynamics crucial for athletes' performance and safety. [PERSON] et al. [26] tackled the less studied concept of effective mass in punch dynamics, showing that existing theoretical models do not fully account for the complexities of real-world impacts. This gap highlights the need for more nuanced research to improve training and reduce injuries. Therefore, we decided to determine the effective mass differently than before, relying on the classical relationship of [PERSON]'s second principle of dynamics:  
\[\text{Effective mass}=\frac{\text{Force pressure}}{\text{Foot acceleration}}\]  
The appropriately chosen effective mass in aekwon-do is an extremely important element of training, affecting the effectiveness of kicks. However, it requires an understanding of the biomechanics of movement and the recognition of the impact of various variables. Therefore, the aim of these studies was to gain knowledge about the influence of the obtained effective mass on the strength of the turning and side kick in the context of lateralization. In this regard, the following research questions were posed: What is the effective mass in the side and turning kicks, and which of these kicks achieve higher values of this variable?