Architectural and Functional Adaptations to Eccentric Training in Adolescent Volleyball Players: A Randomized Controlled Trial

Eccentric exercise is widely used to enhance muscle strength and performance, yet its specific effects on muscle architecture and functional outcomes in adolescent athletes remain insufficiently explored. This randomized controlled trial examined the effects of an eight-week eccentric heel-drop program on triceps surae architecture, strength, and jump performance in adolescent female volleyball players. Twenty-six athletes were randomized to an exercise group (<i>n</i> = 14) or control group (<i>n</i> = 12). The exercise group performed supervised heel-drops three times weekly, while controls continued regular training. Ultrasound assessed the muscle thickness, fascicle length, and pennation angle of the gastrocnemius medialis, gastrocnemius lateralis, and soleus. Strength was measured via dynamometry, and vertical jumps (squat, countermovement, block, attack) were evaluated. The exercise group showed significant increases in gastrocnemius medialis muscle thickness (<i>p</i> = 0.03) and fascicle length (<i>p</i> = 0.002), with no changes in other muscles. While both groups improved strength, no between-group differences emerged. However, the exercise group demonstrated significant improvements in squat, block, and attack jump performance (<i>p</i> < 0.05). Consequently, eccentric plantar flexor training elicited muscle-specific architectural adaptations and improved sport-specific jump performance. Progressive eccentric heel-drop exercises serve as an effective addition to youth conditioning programs to enhance structural and functional outcomes.