A. Nuviala Nuviala, D. Munguía Izquierdo, A. Fernández Martínez, F. Ruiz Juan, and M. E. García Montes, “Typologies of occupation of leisure-time of Spanish adolescents: The case of the participants in physical activities organized”, J. Hum. Sport Exerc., vol. 4, no. 1, pp. 29–39, Jan. 2009.