Fatima Hasan Hassoun, et al. “The Effect of Mental Exercises and Tennis Tools in the Development of Concentration and Intensity of Attention According to the Vienna Psychological System and Front and Rear Impact”. Modern Sport, vol. 18, no. 1, Mar. 2019, pp. 333-42, https://jcopew.uobaghdad.edu.iq/index.php/sport/article/view/1441.