Author(s): JANDOVA, T., STEFFL, M., Institution: CHARLES UNIVERSITY, FACULTY OF PHYSICAL EDUCATION AND SPORT, IC: 00216208, Country: CZECH REPUBLIC, Abstract-ID: 560

INTRODUCTION:
Ultrasound-derived echo intensity (EI) of skeletal muscle is increasingly used as a marker of muscle quality, with higher EI traditionally reflecting greater non-contractile tissue (1). However, evidence suggests that EI is influenced not only by tissue composition but also by muscle architecture and training status (2). Despite growing interest in EI, data in paediatric populations remain scarce, particularly among children with diverse body compositions and training histories. This exploratory study examined associations between isometric knee extensor strength and ultrasound-derived EI in the vastus lateralis (VL) in early adolescent girls.
METHODS:
Six girls (mean age 12.3 years) were purposively selected: two normal-weight, two overweight based on Czech reference values for body mass index (BMI), and two athletes (elite artistic gymnasts). Right VL was assessed at 1/3 of the distal length using a 40 mm linear array probe (7–12 MHz, depth 50 mm, gain 50 dB) with B-mode ultrasound (SonoScape Medical Corp., China). EI was calculated in ImageJ (V.1.54g; National Institutes of Health, USA) as the mean grayscale value (0=black, 255=white) within a polygonal region of interest (ROI). Maximal voluntary contraction (MVC) of the right quadriceps femoris (QF) was measured as peak torque (Nm) using isokinetic dynamometry (Humac Norm, Cybex CSMI, Stoughton, MA, USA) and normalised to body weight (%BW). Exploratory analyses were conducted to describe trends in the variables. The coefficient of determination (R2) was computed as the square of the Pearson correlation between the muscle quality markers and the muscle strength variables.
RESULTS:
Mean EI values were 62.3 a.u. in normal-weight girls, 75.3 a.u. in overweight girls and 75.5 a.u. in gymnasts. Mean peak torque was 92.6 Nm in normal-weight girls, 90.0 Nm in overweight girls and 75.0 Nm in athletes, and relative peak torque was 172.5 %BW in normal-weight girls, 122.6 %BW in overweight girls and 231.0 %BW in athletes. R² = 0.155 indicated a small association between peak torque and EI, while R² = 0.000 indicated no association between %BW and EI.
CONCLUSION:
These exploratory findings suggest a non-linear (U-shaped) relationship between training status and EI, with both gymnasts and overweight girls showing similarly elevated EI despite contrasting strength and functional profiles. This indicates that increased EI may reflect not only intramuscular fat but also training-related architectural adaptations, underscoring the need to interpret EI in context and to include complementary architectural measures in future studies.
References:
1. Stock MS, Thompson BJ. Echo intensity as an indicator of skeletal muscle quality: applications, methodology, and future directions. Eur J Appl Physiol. 2021 Feb;121(2):369-380.
2. Pinto MD, Silveira Pinto R, Nosaka K, Blazevich AJ. Do Intramuscular Temperature and Fascicle Angle Affect Ultrasound Echo Intensity Values? Med Sci Sports Exerc. 2023 Apr 1;55(4):740-750.