Echocardiographic study of structure and functional cardiac profile of football referees - Ruiz Caballero, J. A.; Brito Ojeda, E.; Garcia-Aranda, J. M.; Mallo, J.; Helsen, W.; Sarmiento, S.; Garcia-Manso, J. M.; Navarro Valdivielso, M. E. (The Journal of Sports Medicine and Physical Fitness, 2011)