Sport is considered to be a universal phenomenon in the time and human space. Technically, sport represents any form of physical exercises and movement games which may be spontaneous or competitive, having their origin in the traditional games and in the founding myths of civilization and with a specific founded on the values of the contemporary society (Dauzat, 1971. The functions of sports, as inherited from the Antiquity, emphasize the values within the aforementioned definition. The most important of these functions: the competition function (satisfying the need to compete, maximizing the performance, the connotative function (the need for physical effort), the socializing function (the need for integration, social dialogue and social affirmation), the cultural and the economic function. In this perspective, sport leads to psycho-physical performance, rules, institutionalization and competition, as well as to great leisure activity. There is a complex relationship between sports and society; describes two perspectives on sports. The idealist perspective defines sport as a free, spontaneous activity, separated from everyday life. The instrumental one states that sport is the ideological image of the dominant interests within the current society.
As regards the school curriculum, physical education and sports represent the only discipline within the curriculum which addresses the problem of physical and psychological health of the pre-school, school and university students. By definition, sports activities concern three main components of the human being (biological, psychological and social) and, of course, three finalities: The harmonious development of the body, the psycho-physical balance and the social integration of the individual. Thus, physical education and sports have clear objectives and by practicing them we create a support for the individual's activities at all ages (Curelaru et al., 2010).
Most of the researches investigating the involvement of teenagers and young people in sports' activities analyzed psychological factors, such as motivation and will, corporal scheme, social-cultural and demographic variables: age, gender, social-economic status, level of parents' education, type of school, stereotypes and, values. Due to the fact that sport is an important field within the main life competences, we believe that investigating the predicting factors of sports and movement should be an important objective for sports psychologists.
Developmental psychology has showed that every stage of our life has its specific tasks and characteristics; adolescence, the transition stage between childhood and adulthood, confronts the individual with five psycho-social types of issues: identity, autonomy, intimacy, sexuality and competency (Erikson and Erikson, 1997). The difficulties encounter in achieving the different tasks specific to this stage, as well as the individual particularities may sometimes lead to risk behaviors (substances abuse, violence, delinquency).
Recent studies by Danish et al. (2000) underline the importance of teaching healthy behaviors such as sports in preventing risky behaviors, like the ones mentioned before. Sports can be an important resource that can help teenagers to learn abilities necessary to an effective functioning within the family, school and community: responsible behaviors, internalizing rules, courage, effectiveness, perseverance or tolerance to frustration. Thus, studies regarding bullying and its prevention show that a certain degree of aggressiveness within sports may have positive effects upon controlling bullying at school (Miller et al., 2006; Cashmore, 2008).
Numerous studies have, also, underlined the positive connections between sports participation and high levels of well-being and self-esteem, well-developed teamwork and leadership skills, lower dropout rates, strong academic motivation and discipline (Chu, 1989; Marsh, 1993; Whitley, 1998; Eccles and Barber, 1999; Simons et al., 1999; Videon, 2002).
The social contexts influencing teenagers' development, the family, peer groups, school and leisure groups, mark directly or indirectly, their lifestyle, through the beliefs that they inspire.
In the last decades, there has been a special preoccupation for developing the field of sport psychology and, also, for increasing the public awareness on the importance of physical education, as a discipline, in the school curriculum. In Great Britain, for example, new educational policies related to lifelong learning and the progress of learning communities, have increased the importance of physical education in the academic curriculum. Thus, adopting the new "physical education and sports " terminology extends the learning space of this domain of competence outside the school (Penney, 2007).
During the past years, researches on sport psychology have focused their attention on the relationship between gender and sport and the need to motivate young people for sportive activities. Wellard (2007) states that, even though there are various evidences regarding the benefits of movement and sports, many young people, especially girls, do not allow more time for these essential and entertaining activities. One of the possible explanations is related to the belief that men are more inclined towards sports then women.
Physical education within school is viewed as an instrument for building one's identity and establishing gender roles. Many parents and teachers still believe that girls should not get involved in sports as much as boys and these expectations influence the degree of motivation and participation (Lumpkin, 1984; Shakib and Dunbar, 2004). Other studies underline that the motivation for the involvement in sports and physical activities is different for boys and girls (Uhlir, 1982; Blinde, 1989; Hill, 1993; Sadker and Sadker, 1994; Festle, 1996).
The Australian Statistics Bureau showed that, although the participation rate is comparable for boys and girls (72% for girls and 74% for boys), the reasons are different: all of them are motivated by their parents and their coaches and by winning different prizes, but only boys say they are irresistibly motivated by competition and by the desire to fight the others (Cashmore, 2008).
Gill (1988) investigated the differences regarding the competitive achievement orientation and the participation to sport. Results showed that boys registered higher scores on orientation towards competition and they reported more competitive activities than girls. In exchange, women had higher scores on non-competitive achievements and they reported an interest for the non-sportive and sportive non-competitive activities similar to those of men.
Further studies (Hargreaves, 1994; McRobbie, 1978, 1991; Gill, 1999, 2000) offer evidence concerning the influence of the social context upon the gender roles in sports, the differentiated treatment of evaluating the sportive performance and the trust regarding the sportive performance possibilities.
Several studies, also, emphasized the relationship between demographic factors (age, gender, socio-economic status, socio-cultural factors, the family participation to sport, educators) and children and teenagers' participation in sportive activities (Lin Yang, Telama and Laakso, 1996; Raudsepp and Vira, 2000; Lareau, 2002; Darling et al., 2005; Kamphuis et al., 2008). A complex study, realized on a population in Portugal (Seabra et al., 2008) underlined that age has no influence on the level of involvement in sports...