Reda , D.K.M. et al. 2025. The Effect of Circuit Training According To the Variation of Speed and Time in Improving the Speed Strength, Specific Endurance and Achievement of 400 M Freestyle Runners Under 20 Years. Excellencia: International Multi-disciplinary Journal of Education (2994-9521). 3, 1 (Jan. 2025), 55–70. DOI:https://doi.org/10.5281/.