Filippidou Χ., Loupos Δ., Zafireiadis Σ., and Barkoukis Β. “Intensity and Direction of Precompetitive Anxiety: A Study of the Individual Zones of Optimal Functioning Theory in Swimming”. Inquiries in Physical Education and Sport, vol. 12, no. 2, Apr. 2014, pp. 90-100, https://journals.lib.uth.gr/index.php/inquiries/article/view/1422.