Kyle, Tilly Louise, et al. “Efectos De La Actividad física En El Autoconcepto Y La Autoeficacia En Preadolescentes (Effects of Physical Activity on Self-Concept and Self-Efficacy in Preadolescents)”. Retos, vol. 29, Jan. 2016, pp. 61-65, https://doi.org/10.47197/retos.v0i29.36873.