Physical fitness spurts in childhood: A study in boys - Pereira, Sara; Garbeloto, Fernando; Guimarães, Eduardo; Santos, Carla; Baxter-Jones, Adam; Tani, Go; Freitas, Duarte; Bustamante, Alcibíades; Katzmarzyk, Peter T; Maia, José (Scandinavian Journal of Medicine and Science in Sports, 2021)