Core Training Adaptations in 13–14-Year-Old Female Tennis Players: Effects on Balance and Trunk Rotation Strength

Background: Core stability is the foundational link in the kinetic chain of tennis strokes, yet the specific impact of supplementary core conditioning on the neuromuscular development of adolescent female players remains poorly quantified. This study investigated the effects of an 8-week core training program on dynamic balance and static trunk rotation strength in 13–14-year-old female tennis players. Methods: In this parallel-group randomized controlled trial, 24 female tennis players were assigned to an experimental group (EG; n = 12) or a control group (CG; n = 12). The EG performed a 45–60 min supplementary core protocol (3 days/week) focusing on progressive overload, while the CG engaged in matched-duration low-intensity technical drills. Assessment tools included the Star Excursion Balance Test (SEBT) for dynamic balance and a digital rope dynamometer for static trunk rotation strength (forehand/backhand). Results: Mixed-model repeated-measures ANOVA revealed significant Group × Time interaction effects with large magnitudes. The EG demonstrated significant improvements in right-foot dynamic balance (0.83% increase; p = 0.005), forehand trunk rotation strength (13.41% increase; p = 0.001), and backhand trunk rotation strength (12.00% increase; p = 0.012); the control condition did not result in significant improvements in any variable over the 8-week intervention period (all p > 0.05). Conclusions: An 8-week structured core training program significantly improved right-foot dynamic balance and static trunk rotation strength in adolescent female tennis players relative to technical training alone. These findings support considering core-specific conditioning as a component of training for this population; however, as tennis-specific performance, injury risk, and kinetic-chain function during actual strokes were not directly assessed, claims regarding broader clinical or sport-specific performance benefits require confirmation in future research. Trial Registration: This trial was retrospectively registered in the Iranian Registry of Clinical Trials (IRCT; a WHO ICTRP Primary Registry) on 30 September 2026 (registration number: IRCT20260904070908N1). Prospective registration was not undertaken because it was not required by the approving institutional ethics committee at the time the study was conducted (2019); ethics approval is not regarded as a substitute for prospective registration, and this is acknowledged as a limitation.