Author(s): YING, L., CHENG, R., LI, M., ZHANG, Q.S., Institution: SCHOOL OF ATHLETE PERFORMANCE, Country: CHINA, Abstract-ID: 753

INTRODUCTION:
Dynamic postural stability is a potential injury risk factor, yet performance is highly task-specific such as drop landing (1). Specifically, active initiation introduces horizontal momentum and distinct postural adjustments compared to gravity-driven patterns (2). Standard protocols utilizing fixed drop heights fail to normalize these mechanical disparities. Therefore, this study aimed to determine the differential effects of passive versus active initiation patterns on dynamic stability (Time to Stabilization [TTS] and Dynamic Postural Stability Index [DPSI]) under strictly individualized, CMJ-based impact loads.
METHODS:
Twenty-one male semi-professional athletes (age: 21.5±2.1 yrs; height: 1.82±0.06 m; mass: 74.3±5.8 kg) participated. Drop heights were individualized based on single/double-leg CMJ height. Participants performed three single-leg landing tasks representing distinct neuromuscular constraints: Step-Off (SOF); Step-Out Jump (SOJ)(3); and Single-Leg Jump (SLJ)(4,5). Ground reaction forces were acquired at 1000 Hz using dual 3D force platforms (KWYP-FP6050, Kunwei, China). Participants were instructed to maintain a stable single-leg stance for 20 s post-impact. Data were processed to calculate TTS in Anterior-Posterior (AP) and Medial-Lateral (ML) directions and the DPSI. Linear Mixed Models were employed for analysis.
RESULTS:
Linear mixed models indicated a significant main effect of initiation pattern for DPSI (F = 77.57, p < 0.001), but not for TTS in AP or ML directions (all p > 0.05). The SOF pattern demonstrated lower DPSI values (0.24 ± 0.04) compared to SOJ (0.29 ± 0.03) and SLJ (0.31 ± 0.05) patterns (p < 0.001), with large effect sizes (d = 1.41 and 1.55, respectively). Conversely, no significant differences were observed between the two active patterns (SOF vs. SLJ) (p > 0.05).
CONCLUSION:
The present study demonstrates that active propulsion itself is the primary factor reducing stability quality, regardless of whether the Movement Initiation Patterns involve ipsilateral (SLJ) or contralateral (SOJ) mechanics. While stabilization time (TTS) is conserved across tasks, stability quality (DPSI) is best in the SOF mode. Therefore, the SOF can serve as a standardized drop initiation pattern for assessing dynamic postural stability, whereas active tasks confirm the stability cost of propulsion.