Ruaa Amer Ismaeel and Bushra Kadhum Abdul-ridha 2022. The effect of critical speed exercises and mechanical ability to test the maximum speed of 400m runners under the age of 20 years. Modern Sport. 21, 4 (Dec. 2022), 0044–0050. DOI:https://doi.org/10.54702/ms.2022.21.4.0044.