Influence of Subcutaneous Adipose Tissue and Skeletal Muscle Thickness on Rectus Femoris Echo Intensity in Younger and Older Males and Females

Abstract

Objectives-Ultrasound measurements of muscle echo intensity are commonly used surrogates of muscle composition (eg, intramuscular adipose tissue). However, given that soundwaves are increasingly attenuated with tissue depth, the interpretation of echo intensity may be confounded by adipose and skeletal muscle thickness. Our objectives are to compare the associations between adipose or muscle tissue thickness and rectus femoris echo intensity in younger and older males and females.Methods-Participants included in this analysis were derived from 3 previously published cohorts of younger (<45 years) and older (≥60 years) males and females. Ultrasound images of the rectus femoris were evaluated for muscle thickness, echo intensity, and subcutaneous adipose tissue thickness.Results-Older adults (n: 49 males, 19 females) had a higher body mass index (P = .001) compared with younger adults (n: 37 males, 49 females). Muscle thickness was negatively associated with echo intensity in older males (r = À0.59) and females (r = À0.53), whereas no associations were observed in younger males (r = 0.00) or females (r = À0.11). Subcutaneous adipose tissue thickness displayed no associations with echo intensity in any group.Conclusions-Despite the known influence of subcutaneous adipose tissue thickness on beam attenuation, we observed no association with muscle echo intensity, indicating that adipose tissue correction may be required to better understand muscle echo intensity across differences in adiposity. The negative associations between muscle thickness and echo intensity in older, but not younger adults, suggests these associations may be related to the co-occurrence of skeletal muscle atrophy and intramuscular adipose tissue infiltration with advancing age.

The filling factor of the sEMG signal at low contraction forces in the quadriceps muscles is influenced by the thickness of the subcutaneous layer

“…This striking difference in the type of sEMG activity at low contraction forces between males and females (pulsatile vs. continuous) is thought to be due to the differences in the subcutaneous layer thickness between the two genders. Indeed, we found that, in the vastus muscles, the subcutaneous layer was remarkably thinner in males (5.0, 5.7 mm) than in females (10.3, 11.3 mm), in agreement with Caresio et al (2015) and Paris et al (2022). We propose that the thickness of the subcutaneous layer is a major determinant for the type of sEMG activity at low contraction forces.…”

Usefulness of muscle ultrasound in appendicular skeletal muscle mass estimation for sarcopenia assessment

“…Some studies reported that muscle EI may be associated with muscle strength and functional status [ 23 – 25 ]. Previous research has reported that muscle EI is negatively correlated with MT in older adults [ 26 ]. Another study reported that changes in muscle EI were significantly associated with changes in BMI [ 27 ].…”