Pérez-Villalba, M., García-Fernández, J., Gómez-Chacón, R., & Fernández-Martínez, N. (2018). Group exercise training in sport centers and its value as a retention element. SPORT TK-EuroAmerican Journal of Sport Sciences, 7(2), 17–26. https://doi.org/10.6018/sportk.343061