Excessive sedentary time and low cardiorespiratory fitness in European adolescents: the HELENA study - Martinez-Gomez, David; Ortega, Francisco B.; Ruiz, Jonatan R.; Vicente-Rodriguez, German; Veiga, Oscar L.; Widhalm, Kurt; Manios, Yannis; Beghin, Laurent; Valtuena, Jara; Kafatos, Anthony; Molnar, Denes; Moreno, Luis A.; et al. (Archives Of Disease In Childhood, 2011)