Context: Core control and strength are important for reducing the risk of lower-extremity injury. Current evidence on the effect of core training in male adolescent athletes is limited, and other investigations into the effects of core training often emphasized core strength only. Objective: To examine whether core training emphasizing both control and strength of the trunk and hip would improve joint kinematics during landing, sports performance, and lower-extremity muscle strength in adolescent male volleyball athletes. Design: Single group pretest and posttest design. Setting: University laboratory. Participants: Sixteen male participants (age: 13.4  y, height: 167.8 [8.6] cm, mass: 58.6 [13.9] kg, and volleyball experience: 3.8 [1.5] y) from a Division I volleyball team at a junior high school. Main Outcome Measurements: Kinematics of the trunk and lower-extremity during box landing and spike jump landing tasks, volleyball-related sports performance, and isokinetic strength of hip and knee muscles were assessed before and after a 6-week core training program. Results: After training, the participants demonstrated decreased trunk flexion angle (P =.01, Cohen's d = 0.78) during the box landing task and reduced the maximum knee internal rotation angle (P =.04, Cohen's d = 0.56) during the spike jump landing task. The average isokinetic strength of hip flexors and external rotators, and knee flexors and extensors also significantly increased (P =.001, Cohen's d = 0.98; P =.04, Cohen's d = 0.57; P =.02, Cohen's d = 0.66; P =.003, Cohen's d = 0.87, respectively); however, sports performance did not show significant changes. Conclusions: A more erect landing posture following training suggests that the core training program may be beneficial for improving core stability. The long-term effect of core training for knee injury prevention needs further investigation.
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