Kelly E. Joniak, Hannah E. Cabre, Sam R. Moore, Alex N. Ladan, Abbie E. Smith-Ryan, FACSM. University of North Carolina at Chapel Hill, Chapel Hill, NC.

BACKGROUND: Fat-free mass index (FFMI, kg/m2) and regional muscle characteristics may provide direct insight into athletic performance and injury prevention. Underutilized and often misunderstood, FFMI specifies individual potential to accumulate fat-free mass (FFM; lean mass and bone mineral content) relative to height. FFMI has been shown to be useful for tracking changes in FFM and monitoring return to play from injury, particularly in females. The purpose of this study was to evaluate the relationship between total and regional body composition and muscle characteristics with aerobic capacity, speed, power, and agility performance in Division I female soccer players. METHODS: Eighteen female soccer players (mean ± SD; Height= 165.3±5.1cm; Weight= 63.6±7.3kg; FFMI= 18.4±1.2 kg/m2; %fat= 22.9±4.9kg) completed a total body dual-energy x-ray absorptiometry scan to determine total body percent fat (%fat), FFM, and right and left leg lean mass (RLM and LLM, respectively). FFMI was determined as FFM/height (m2). A panoramic ultrasound scan of the right vastus lateralis muscle was used to determine cross-sectional area (mCSA) and echo intensity (EI) of the vastus lateralis. Performance testing included vertical jump (VJ; cm), beep test (BT, m), 10m and 30m dash (s), and right and left Illinois agility tests (ILR and ILL, respectively; s). Pearson product moment correlations were utilized to evaluate these relationships. RESULTS: FFMI was significantly positively associated with VJ (r=0.681; p=0.002). EI had a significant positive association with BT (r=0.471; p=0.048). %fat was significantly negatively associated with VJ (r=-0.667; p=0.002), BT (r=-0.538; p=0.021), and positively associated with 30m (r=0.491; p=0.039), ILR (r=0.578; p=0.012), and ILL (r=0.668; p=0.002) tests. mCSA, FFM, RLM, and LLM were not significantly related to any performance metrics. CONCLUSION: FFMI and %fat may influence power-based movements where greater FFMI and lower %fat benefited VJ. EI may positively impact aerobic performance, while %fat may negatively affect aerobic capacity. Measuring FFMI, EI, and %fat can inform nutrition and training interventions to achieve body composition goals benefiting performance and return to play.

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