Influence of muscle depth and thickness on ultrasound echo intensity of the vastus lateralis.

Background: Ultrasonography is used to evaluate muscle quality (i.e. echo intensity [EI]), but an attenuation of ultrasound waves occurs in deeper tissues, potentially affecting these measures.
Purpose: To determine whether muscle thickness (MT) affects EI and if EI varies between the superficial and deep portions of the muscle.
Materials and Methods: MT, EI, subcutaneous adipose tissue thickness (SAT), tissue depth (DIS _DEEP ), and EI of the overall (EI _FULL ) as well as deep (EI _DEEP ) and superficial (EI _SUPF ) portions of the vastus lateralis (VL) were assessed in 33 resistance-trained males using ultrasonography. The difference (EI _DIFF ) between EI _SUPF and EI _DEEP was calculated. Mean differences between EI _FULL , EI _SUPF, and EI _DEEP were analyzed using a repeated-measures analysis of variance (ANOVA). Relationships between measures of muscle depth/ thickness and EI were examined using Pearson's r .
Results: EI _SUPF was greater than EI _DEEP ( P  < 0.001) and EI _FULL ( P  < 0.001). MT was negatively correlated with EI _FULL ( P  < 0.001) and positively correlated with EI _DIFF ( P  < 0.001). SAT was not correlated with any EI measure, but DIS _DEEP was positively correlated with EI _DIFF ( P  < 0.001).
Conclusion: EI of the VL is heterogeneous, as the deeper portion produces lower values than the superficial portion. Thicker muscles present lower EI but have greater discrepancies in EI between the superficial and deep portions. Although SAT was not correlated with EI, DIS _DEEP was related to EI _DIFF , demonstrating that the combination of MT and SAT should be considered when evaluating muscle quality. Future research is necessary to determine if changes in EI following resistance training are driven by increases in MT.