The application of ultrasound sarcopenia index in sarcopenic population

Aging leads to progressive motor system decline, which can result in sarcopenia, defined as the age-related loss of muscle mass and function. Architectural changes, epitomized by a decrease in fascicle length (Lf) and muscle thickness (MT), provide a useful signature of sarcopenia. Their ratio (Lf/MT), named ultrasound sarcopenia index (USI), is a new parameter proposed for evaluating changes in muscle geometric proportions associated with muscle atrophy but lacks application in a sarcopenic population. This study aimed to explore vastus lateralis USI in a sarcopenic population.

In a sample of 139 older adults (54% females), recruited from Italy and Slovenia, we assessed muscle architecture using ultrasound imaging to measure Lf, MT, pennation angle (PA), and USI. We assessed handgrip strength, sit-to-stand test, and physical performance with timed up-and-go and gait speed. Appendicular lean mass was assessed with dual x-ray absorptiometry. Sarcopenia was classified using the EWGSOP2 and SDOC classifications.

Sarcopenia prevalence was 15.1% and 30.9% when classified by the EWGSOP2 and SDOC classifications, respectively. Differences in muscle architecture were observed between sarcopenic and non-sarcopenic groups, with MT showing the largest effect size (Cohen's d EWGSOP2: 0.86; SDOC:0.77). USI was higher in sarcopenic compared to non-sarcopenic individuals classified with EWGSOP2 (5.33 ± 1.30 vs 4.59 ± 0.94, p = .011, Cohen's d:0.69), confirming its sensitivity in detecting sarcopenia.

We showed that increased USI values are associated with sarcopenia. This study shows USI as a sensitive, non-invasive marker for sarcopenia classification, supporting its use in clinical screening and monitoring of muscle changes in older adults.