Do hip and groin muscle strength and symptoms change throughout a football season in professional male football players? A prospective cohort study with repeated measures - van Klij, P.; Langhout, R.; van Beijsterveldt, A. M. C.; Stubbe, J. H; Weir, A.; Agricola, R.; Fokker, Y.; Mosler, A. B.; Waarsing, J. H.; Verhaar, J.; Tak, I. (Journal of Science and Medicine in Sport, 2021)