Associations Between Body Composition Measurements and Muscle Ultrasound Parameters Amongst Children and Adolescents with Overweight and Obesity

<b>Background/Objective:</b> Pediatric obesity negatively impacts metabolic and musculoskeletal health, particularly muscle quality and function. Ultrasound-derived measures like muscle thickness and echo intensity, combined with body composition data, provide a more comprehensive assessment of muscle status in this population. The purpose of our study was to examine the relationship between anthropometric measurements, muscle strength, and bioelectrical impedance estimations with ultrasound-derived indicators such as subcutaneous fat and quadriceps femoris thickness, as well as muscle quality, through EI. <b>Methods:</b> This cross-sectional study included Hispanic children aged 6 to under 18 years with overweight or obesity (BMI ≥ 85th percentile per CDC standards). Participants were recruited consecutively from outpatient visits. All eligible children were invited for a standardized nutritional assessment, and those who consented were included. <b>Results:</b> The study included 294 children and adolescents (153 boys, 141 girls) with overweight or obesity, showing significant sex differences in anthropometric and body composition variables. Girls had higher intramuscular adipose tissue (IMAT) (<i>p</i> < 0.001), while boys had more lean and musculoskeletal mass. Body fat percentage was significantly correlated with muscle echo intensity (EI corrected: R² = 0.264, <i>p</i> < 0.001; EI uncorrected: R² = 0.242, <i>p</i> < 0.001) and with IMAT (R² = 0.268, <i>p</i> < 0.001). These associations were stronger in girls. Linear models identified body fat and BMI percentile as key predictors of muscle quality indicators (<i>p</i> < 0.001). <b>Conclusions:</b> This study found that higher body fat in children and adolescents with overweight or obesity is linked to poorer muscle quality, and especially increased echo intensity and intramuscular fat. Ultrasound proves useful for early, non-invasive detection of musculoskeletal changes, emphasizing the need to assess both muscle size and quality.