Although previous research has investigated the training-specific adaptations to training in adults, there is a paucity of research aimed at investigating these adaptations in adolescent athletes. As such, adolescent athletes` training-specific adaptations from three different training interventions were investigated in this study. Sixteen adolescent athletes participated in this study, whereby eight performed both training interventions and eight the non-training control. Pre- and post-testing was performed for each intervention with the testing battery: ultrasonography of the vastus lateralis and lateral gastrocnemius, countermovement jump, squat jump, and isometric mid-thigh pull. The resistance training group had large significant increases in isometric mid-thigh pull relative peak force (p<0.01, g=0.85 (-0.01, 1.71)) and vastus lateralis fascicle length (p=0.04, g=0.94 (0.07, 1.80)). The gymnastics and plyometric group demonstrated large significant changes in vastus lateralis pennation angle (p=0.03, g=-0.94 (-1.81, -0.08)) and fascicle length (p=0.03, g=1.07 (0.19, 1.95)), and moderate significant increases in lateral gastrocnemius thickness (p=0.01, g=0.63 (-0.21, 1.47)) and eccentric leg stiffness (p=0.03, g=0.60 (-0.24, 1.44)). No significant changes were observed for any variables in the non-training group. The resistance training evoked increases in lower-body force producing capabilities, whereas the gymnastics and plyometric training evoked changes in muscle structure and inherent muscle qualities. ABSTRACT FROM AUTHOR
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