Lower limb asymmetries in elite junior female vault gymnasts

Due to long-term repetitive training of specific techniques, competitive vaulting gymnasts are prone to develop lower limb functional asymmetry. The symptom of lower limb functional asymmetry can seriously impair vaulting performance and is a major contributing factor to sports-related injuries. This study aimed to analyze the effect of key factors, including functional asymmetry in explosive power and balance ability among elite junior female vaulters, on run-up velocity and jumping ground reaction force. We conducted a series of assessments on twenty elite junior female vault specialists using the Noraxon MR3 wireless surface electromyography system, Kistler 3D force plates, and Tci-System infrared velocimetry. The assessments include countermovement jump (CMJ), Y-balance test (YBT), surface electromyography (sEMG), and vault trials. We employed paired-sample t-tests to analyze bilateral differences between dominant limb and non-dominant limb in jumping ground reaction force, balance, and muscle activation contributions. Pearson correlation analysis revealed the relationship between the bilateral asymmetry index (BAI) and vaulting run-up velocity or jumping ground reaction force. Segmented regression was employed to investigate the potential threshold effects of BAI on run-up velocity and jump ground reaction force. (1) We observed significant inter-limb differences in CMJ power production (P < 0.05), particularly in the vertical direction where the asymmetry index reached approximately 18.35%. (2) The YBT reach distance and center of pressure (COP) displacement both exhibited significant bilateral asymmetry (P < 0.05). The balance BAI were 3.25%, 3.04%, and 3.35% for the anterior (A), posteromedial (PM), and posterolateral (PL) directions. (3) The gluteus maximus showed significant inter-limb differences in muscle contribution rate (P < 0.05), while the rectus femoris, hamstrings, tibialis anterior, and gastrocnemius exhibited significant differences (P < 0.01). (4) The CMJ power asymmetry index exceeding 10.4% showed significant differences in jumping ground reaction force (P < 0.05), while exceeding 14.8% demonstrated significant differences in run-up velocity (P < 0.05). The YBT balance BAI showed no significant relationships with either jumping ground reaction force or run-up velocity (P > 0.05). Conclusion: Lower-limb power and balance asymmetries in elite junior female gymnasts exhibited measurable threshold ranges Significant disparities exist in muscle contribution rates between dominant limb and non-dominant limb. The power asymmetry may influence vaulting run-up velocity and jumping ground reaction force beyond specific thresholds.