Effects of region of interest size and measurement location on ultrasound-derived hamstrings muscle quality indices in children.

OBJECTIVES: This study primarily examined sex differences in ultrasound-derived hamstring muscle quality in physically active prepubertal children and secondarily evaluated the effects of region of interest selection and measurement site on these indices. METHODS: Twenty-six prepubertal children (9-11 years, 13 girls) underwent quantitative ultrasound assessment of the semitendinosus and biceps femoris at five measurement sites along the femur. Mean uncorrected echo intensity, corrected echo intensity, echovariation, and texture features were extracted from longitudinal ultrasound images using two region of interest approaches: maximal and standardised rectangular region of interest. RESULTS: Linear mixed-effects models indicated that girls exhibited higher corrected echo intensity and homogeneity and lower contrast and correlation values in the semitendinosus (p < .05), while no sex differences were found in the biceps femoris (p > .05). Region of interest size affected the values of corrected echo intensity, echovariation, and correlation, with higher values observed in maximal region of interest, without altering group-level findings (p > .05). Corrected echo intensity was greater in the biceps femoris than the semitendinosus. Corrected echo intensity varied across the measurement sites, showing higher values at the proximal and proximal-middle locations (p < .05). CONCLUSIONS: Region of interest size, sex, muscle, and measurement site influence muscle quality parameters in prepubertal children. Site- and muscle-specific differences underscore the need for standardised assessment protocols.