## 1 Introduction and Literature Review  
The limitation of time and number of classes demands teachers to use the most effective methods and exercises that have beneficial effects on students' health and future motivation to be physically active. Teachers should always look for new methods, approaches on how to motivate and activate their students for better performance and results during the physical education (PE) classes. Strength and endurance training produce significantly different or even opposite outcomes. Aerobic endurance training reduces the activity of glycolytic enzymes and increases the number of intracellular energy storages, the activity of oxidative enzymes, the number of capillaries in muscles, and the density of mitochondria [1]. Strength training, on the other hand, has nearly opposite results to these factors, although both training types increase the number of intracellular energy storages. Moreover, endurance training mostly maintains or even decreases the size of muscle fibers whereas strength training increases them [2]. Overall, endurance training increases aerobic processes, and strength training increases muscle strength, anaerobic processes, and power production. Applying a short but intensive strength training program (up to 6 weeks) can lead to significant changes in some parameters in strength performance, especially in overall strength and neural adaptation. On the other hand, it is not possible to achieve any significant changes in muscle hypertrophy [3]. Combining these two training methods, strength and endurance training (commonly known as concurrent training), appears to be quite efficient since most of the studies on athletes regarding combined training have led to positive results in both strength and endurance performances [4; 5]. [PERSON] et al. noticed in their study that the combined strength and endurance training group gained as much strength as the group that did only strength training; the first group also improved their maximal oxygen uptake as much as the group that did only endurance training [6]. From _A Meta-Analysis Examining the Interference of Aerobic and Resistance Exercises_, it is known that the total power is the major variable affected by concurrent training, and it does not compromise muscle hypertrophy and maximal strength development [7]. However, explosive strength gains may be attenuated [8]. Moreover, studies found that combination training positively affects the maximal strength of lower limbs in untrained and moderately trained individuals [9; 10]. Other studies found protentional health benefits on cardiovascular, neuromuscular, hormonal, immunological, virological, and body composition parameters. These changes in the combined training program had more or less the same benefit compared with just one of these individually [11]. The American College of Sports Medicine recommends combining aerobic and resistance training for its advantages in contrast to strength or endurance training alone [12]. Concurrent training has not been fully investigated, and there are still many questions. The effect of this training is a multidimensional phenomenon, influenced by many physiological and nonphysiological factors such as type of exercise, training background, muscle groups involved, and inter-individual variations [13]. Volleyball training is commonly used to improve skill-related aspects of the game while also enhancing health-related fitness variables. Studies that investigate the effect of volleyball training on students found higher aerobic capacity [14; 15], better explosive strength, muscular endurance, flexibility [16], functional strength, speed, coordination skills, elasticity, and balance [17] with low risk of injury; this makes volleyball an effective tool in physical education classes. Nevertheless, according to [PERSON], a limited number of studies have investigated the effects of small-sided games in volleyball on physical fitness in children and adolescents [18].