Soccer is the most popular sport in the world, with about 200 million participants including both sexes and all age groups [1]. Because of its popularity, it has often been suggested that soccer may help prevent or cure health problems round the world [2]. However, despite the perception that soccer is a relatively safe sport, it is one of the most common causes of sport injuries among youth [3]. Therefore, elite youth soccer players are exposed to the risk of a variety of sports injuries which may occur for a variety of reasons. It is important that therapists are accurate in testing and cautious in making decisions when treatment is required [4-6]. They also need to have a good understanding of the body composition of youth soccer players. Generally, athletes’ body components appear visually different to those of non-athletes. However, it needs to be said that the body system uniformly applied treatment for athletes is based on visual classification only [7,8]. Therefore, a more systemic and professional approach is required. In a previous study, it was found that body components of athletes may show different tendencies to those of non-athletes [8]; but there has been a lack of professional studies relating specifically to the body components of youth soccer players. Many athletes, including soccer players, commonly use electrotherapy because it is frequently used for the treatment of musculoskeletal disorders [8,9]. Electrical characteristics are generally important factors in electrotherapy because they affect electric strength, which increases the effectiveness of rehabilitation [10]. In our study, we focus mainly on physical therapy and whether it should be applied differently based on the differences shown to exist between athletes and non-athletes. In this way, we have contributed to current research relating to sports physical therapy and its clinical application.

The soccer player subjects markedly showed a lower total impedance (202.7 ± 7.8 Ω) compared to the non-athletes (221.7 ± 12.9 Ω) (Figure 2(A-a)). In both legs, there was a particularly significant difference between right (young soccer players: 204.0 ± 6.4 Ω nonathletes: 236.2 ± 11.2 Ω) and left sides (young soccer player: 206.7 ± 6.7 Ω non-athletes: 239.5 ± 10.5 Ω) (Figure 2(A-b)). The soccer players (11.1±1.1 kg) showed higher skeletal muscle mass in comparison with the non-athletes (10.1 ± 1.7 kg) (Figure 2(B-a)), especially in both legs, where there was a significant difference between right (young soccer players: 11.0 ± 0.2 kg, nonathletes: 9.6 ± 0.3 kg) and left sides (young soccer players: 11.0 ± 0.2 kg, non-athletes: 9.5 ± 0.3 kg) (Figure 2(B-b)). Furthermore, the soccer players showed higher lean/ideal lean × 100% (113.3% ± 0.9%) than non-athletes (106.9% ± 1.0%) (Figure 2(C-a)). Again, in both legs, it could be seen that there was a significant difference between right (young soccer players: 119.7% ±

1.4%, non-athletes: 108.4% ± 1.5%) and left sides (young soccer players: 118.8% ± 1.4%, nonathletes: 107.5% ± 1.9%) (Figure 2(C-b)). The soccer players also showed lower rheobase and higher chronaxie compared to the non-athletes (Figure 3(A)). However, all subjects showed no significant differences on rheobase and chronaxie (Figures 3(B-a) and (C-a)). A gender comparison for the same values showed a similar pattern (Figures 3(B-b) and (C-b)).

Soccer is a sport that is based on power and elaboration of the lower extremities [11]. It necessitates the sudden redirection of the body when following the ball and a player has to run to achieve a good position when in attack or defense. It also requires that a ball is kicked in order to shoot or pass using a combination of strength and finesse [12]. Therefore, a professional soccer player’s body may be thought to be different to that of a non-athlete, especially in terms of the significant difference between the lower extremities in comparison to the remainder of the body structure. Soccer is also one of the most common causes of injuries such as musculoskeletal disorders of the lower extremities. That is why it was thought that professional soccer players suffer from many of these disorders. We focus our research on this area and in particular on the youth soccer player. A young soccer player’s body is slightly different to that of a professional soccer player. However, there are differences in non-athletes of a similar age. There had been few studies performed which particularly focus on the physical therapy of youth soccer players, and as a result, all of our measurements strictly dealt with the differences between youth soccer players and non-athletes. In terms of physical fitness, body composition is used to explain the percentages of fat, bone and muscle in human bodies. Because muscular tissue takes up less space in our body than fat tissue, our body composition, as well as our weight, determines our leanness. Two people of equal height and body weight may look totally different from each other because they have a different body composition, which is derived from many factors. First, birth weight and weight trajectories up to 24 months, associated with particular adult body composition (especially fat-free mass) [13]. Second, physical activity and particular body composition are related in adolescents [14]. It has also been found that body composition is associated with the aging process, having a tendency to

gain fat mass and lose lean tissue in both bone and muscle, even when the weight does not change [15]. Measuring body composition in humans is usually carried out in response to the need to describe either deficiencies or excesses of a component that is thought or known to be related to health risk [16]. Many of the previous conventional body composition measurement methods are based on assumptions that are violated in the very obese state [17]. According to our results, the soccer players show significant differences in some parts, especially in the lower extremities. These differences have great implications. Upon assessing our measurements, we had to approach youth soccer player rehabilitation in a different way to the rehabilitation of non-athletes. In electrotherapy, which is frequently used for the treatment of youth soccer players, the differences of body components were considered important. The soccer players that had low fat and much skeletal muscular mass had to have more electrotherapy application time. In terms of body electrical characteristics, our results revealed a number of important things. Each person has their own body electrical characteristics and in order to understand these, we used rheobase and chronaxies in our measurements. Rheobase is a measure of membrane excitability. In neuroscience, rheobase is the minimal current amplitude of infinite duration (in a practical sense, about 300 milliseconds)

that results in the depolarization threshold of the cell membranes being reached, such as an action potential or the contraction of a muscle [18]. Chronaxie is the minimum time required for an electric current double the strength of the rheobase, to stimulate a muscle or a neuron. Chronaxie, a historically introduced excitability time parameter for electrical stimulation, has been assumed to be closely related to the time constant of the cell membrane [19]. That is why the differences of body electrical characteristics when electrotherapy is employed are important. Rheobase and chronaxie are commonly accepted as the principle parameters predicting the efficacy of electric stimulation [20]. This means that youth soccer players require a lower strength compared to non-athletes on application electrotherapy. Based on the results of our study, we can provide an important basis for selection of electric strength when applying electrotherapy on youth soccer players. In other words, the youth soccer players require less electric strength for rehabilitation or therapy compared to non-athletes (Figure 4). It is necessary to consider taking this into account prior to applying electrotherapy [21,22]. The major limitation of this study is the lack of measured information about other types of athlete. However, through a systemic and professional approach, we can be accurate in testing and cautious in making decisions when treatment is needed. Importantly, we can develop a tailored rehabilitation program and accomplish an effective electronic therapy treatment. If future studies are performed including diverse types of athletes, then they will further contribute to the development of clinical physical therapy and sports physiccal therapy in particular.