Comparison of the IPAQ-A and actigraph in relation to VO2max among European adolescents: the HELENA study - Ottevaere, C; Huybrechts, I; De Bourdeaudhuij, I; Sjöström, M; Ruiz, J R; Ortega, F B; Hagströmer, M; Widhalm, K; Molnár, D; Moreno, L A; Beghin, L; Kafatos, A; Polito, A; Manios, Y; Mártinez-Gómez, D; De Henauw, S (J Sci Med Sport, 2011)