salim, ahmed, Kadum, S. and Khaleel, M. 2022. Fartlek exercises and their effect on molecular biology (vascular endothelial growth factor-basic fibroblast growth factor) and some physical variables for players 800m arena and field for youth. Al-Rafidain Journal For Sport Sciences. 25, 77 (Aug. 2022), 127–142. DOI:https://doi.org/10.33899/rjss.2022.175434.