## 1 Introduction  
If the goal of resistance training were only to increase muscular strength, then the choice of exercises would be dictated by the selection of those that maximize this motor ability based on the percentage of external load above 70% 1 RM [1; 2]. However, the specificity of a given sports discipline is a key factor in transferring strength and power into discipline-specific skills [3; 4]. Furthermore, resistance training is a significant means of reducing the risk of injury [5]. Considering that achieving elite sports level is a long-term process, we increasingly see the use of innovative training methods aimed at maximizing the athlete's motor performance. Therefore, the periodization of the training program is a key element that determines the optimization of particular training micro and mesocycles. Depending on the macrocycle, the training loads should be increased gradually and periodically allowing for physiological adaptations to take place. In resistance training, variables such as load, bar velocity, the number of repetitions and sets, as well as movement tempo, and rest intervals between sets have a direct impact on the effectiveness of the training process [6]. Additionally, exercise selection plays a significant role in training effectiveness [7; 8; 9]. However, one training variable (movement tempo), is often neglected in the periodization of training [10]. This variable includes movement tempo. Resistance exercises have two types of movement tempo: unintentional and intentional. To clarify, a slow tempo can inadvertently occur during resistance training where a heavy load or the manifestation of fatigue is primarily responsible for a slower movement (i.e., increased duration of the repetition) [11]. On the contrary, an intentional slow tempo can be purposefully used if the load is light enough to control the movement and fatigue does not influence one's ability to control the velocity of the bar or other training device. Consequently, conscious and intentional control of the movement tempo is only possible to a certain extent [12]. During concentric contractions, strength is a limiting factor of movement tempo. On the other hand, during eccentric actions even loads above 100% of 1 RM can be controlled to some extent. The tempo is often described using a sequence of digits (e.g., 3/0/2/0), where each digit defines the duration of a particular phase of the movement, irrespective of whether the movement tempo is intentional or unintentional. Therefore, the literature suggests using a four-digit combination that describes the eccentric, isometric/transitional, concentric, and isometric/transitional phases of movement [10]. For example, 3/0/2/0 denotes a 3 s eccentric phase, no intentional isometric pause during the transition phase, a 2 s concentric phase, and no pause between the completion of the concentric phase and the beginning (eccentric phase) of the next repetition. Changes in movement tempo affect the number of performed repetitions in a single set, the time under tension (TUT), and the maximum possible load lifted during a resistance exercise [6]. According to some studies, the number of possible repetitions decreases as the total intended TUT of an exercise with the same load increases. If the relation between movement tempo, number of repetitions, and the TUT is considered, they are not mutually exclusive, as they all affect each other. Hence, modification of movement tempo can indirectly cause a change in the training load during a single training session, or a whole training microcycle [10; 13; 14]. Considering the main objective of the study, the differences between UNI and BIL resistance training must be taken into account. Because the method of multi-joint exercise or the isolated form of the unilateral (UNI) or bilateral (BIL) setting is one of the basic variables in the modification of training programs, which plays a fundamental role in the intensification of particular training cycles [15].