Acute Modulation of Segmental Angular Momentum by Loaded Whole-Body Vibration During Baseball Batting in Adolescent...

Baseball batting requires rapid coordination of multiple body segments as the movement progresses from preparatory loading to trunk rotation and bat-ball contact. Although whole-body vibration (WBV) has been used as a short-duration conditioning method, little is known about how vibration combined with different external loads alters segmental rotational behavior during baseball batting, particularly in adolescent athletes. This study examined phase-specific changes in segmental angular momentum following unloaded and loaded WBV conditions.

Thirty-two national-level adolescent male baseball players were randomly allocated to four conditions: Non-Vibration (Non-Vib), unloaded WBV (Vib), 30% one-repetition maximum combined with WBV (30% 1RM + WBV), and 50%1RM combined with WBV (50% 1RM + WBV). Participants completed a 60-s partial-squat heel-raise conditioning task under their assigned condition, followed immediately by three maximal-effort batting trials. Vibration conditions were performed at 50 Hz with a displacement amplitude of 2 mm. Three-dimensional motion data were obtained using the Kwon3D system, and segmental angular momentum was evaluated during the backswing, hip rotation initiation, and bat-ball contact phases.

Intervention-related differences were concentrated in the early phases of the swing. During the backswing, significant group effects were observed for left-shank Z-axis, right-upper-arm Z-axis, right-forearm Z-axis, trunk Y-axis, and left-forearm Y-axis angular momentum (all p < 0.05), with effect sizes ranging from η² = 0.297 to 0.399. Most significant post hoc comparisons involved the 30% 1RM + WBV condition. During hip rotation initiation, trunk Z-axis angular momentum differed significantly between the 30% 1RM + WBV and 50% 1RM + WBV conditions, while left-thigh Z-axis angular momentum was greater in the 30% 1RM + WBV condition than in the unloaded WBV condition (both p < 0.05). No significant between-group differences were detected for segmental or whole-body angular momentum during the bat-ball contact phase.

WBV combined with external loading produced phase- and segment-specific alterations in angular momentum during adolescent baseball batting. The 30% 1RM + WBV condition showed the most consistent differences, particularly during the backswing and hip rotation initiation phases, whereas increasing the load to 50% 1RM did not produce systematically greater responses. These findings suggest that moderate-load WBV may modify the organization of segmental rotational motion during the preparatory and early acceleration phases of batting. Further research is needed to determine whether these acute biomechanical changes translate into improvements in batting performance.