The Results from This Study Showed That Following Aneccentric Elbow Flexor Training Program, There Was an Increase In Strength Andmuscle Thickness of the Elbow Flexors In Young Boys. the Difference In Thechanges In the Training Arm Between the Maturational Groups Was Non-Significant(P > 0.05), For Both Strength and Muscle Thickness. These Results Indicatethat Training Had the Same Affect on Muscle Strength and Thickness In Both Maturationalage Categories.