Monitoring training load in youth soccer players: effects of a six-week preparatory training program and the association between external and internal loads - Lechner, S.; Ammar, A.; Boukhris, O.; Trabelsi, K.; Glenn, J. M.; Schwarz, J.; Hammouda, O.; Zmijewski, P.; Chtourou, H.; Driss, T.; Hoekelmann, A. (Biology of Sport, 2023)