Elghoul, Y.; Trabelsi, K. .; Masmoudi, L. . . . .; Ben Kahla, A. . .; A. Souissi , M. .; C. T. Clark, C. .; Boukhris, O. .; M. Glenn, J.; Frikha, M. . . TRAINING AND FITNESS VARIABILITY IN ELITE YOUTH SOCCER: PERSPECTIVES FROM A DIFFICULTY PREDICTION MODEL. Kinesiology 2022, 54, 25-35.