Relationship Between Echo-Intensity Bands of the Vastus Lat-Eralis and Rectus Femoris Muscles and Torque Parameters of Knee Extensors in Soccer Players

Background: Echo intensity (EI) derived from ultrasound imaging is widely used to assess muscle quality and has been proposed as a potential indicator of neuromuscular performance. Recently, EI band analysis has been suggested as an alternative approach to provide additional information beyond mean EI. However, evidence linking EI bands to functional outcomes remains limited. Methods: Forty-eight male soccer players (26.2 ± 3.6 years) underwent ultrasound assessment of the vastus lateralis (VL) and rectus femoris (RF) muscles. EI was analyzed as mean values and as pixel distribution across five bands (0–50, 51–100, 101–150, 151–200, and 201–255 A.U.), with correction for subcutaneous adipose thickness. Knee extensor peak concentric torque and total work were assessed using isokinetic dynamometry at 60°/s. Generalized linear regression models were used to examine associations between EI variables and mechanical outcomes. Results: No significant differences were observed between limbs for EI mean or EI band distribution in either muscle. The 0–50 A.U. band exhibited the highest pixel percentage for both VL and RF. Mean EI of the RF was negatively associated with peak torque (β = −4.10; 95% CI: −7.35 to −0.86) and total work (β = −3.89; 95% CI: −6.34 to −1.45) of the right knee extensors. No significant associations were found for EI bands or for any EI variables of the VL muscle. In male soccer players, mean EI of the rectus femoris, but not EI band distribution, is associated with knee extensor torque and work output. Conclusions: These findings suggest that mean EI remains a more informative indicator of muscle quality related to strength performance than band-based EI analysis in this athletic population.