Reference Values of Quadriceps Muscle Thickness Measured by Point-of-Care Ultrasound by Sex and Age Groups in Older Adults.

Sarcopenia is an age-related skeletal muscle disorder characterized by decreased muscle mass, strength, and physical function, which increases the risk of adverse outcomes in older adults. Recently, ultrasound has emerged as a practical tool for estimating muscle thickness as a proxy for muscle quantity. However, standardized protocols, reference data, and diagnostic cut-off values for ultrasound-based muscle assessment remain lacking. This study pooled participants from three cohorts in which quadriceps muscle thickness was assessed in B-mode with a linear probe using point-of-care ultrasound (POCUS). Of 391 participants, 389 were included in the final analysis. Age was categorized into five-year groups (65-69, 70-74, 75-79, 80-85, and over 85 years old). Means and standard deviations (SD) of quadriceps thickness were calculated by sex and age group. Mean age was 77 ± 7 years. Quadriceps muscle thickness followed a normal distribution with a standard deviation of 0.5 cm. Mean thickness declined with advancing age. Our pooled analysis found a mean quadriceps muscle thickness of 2.0 cm. The decline with advancing age was modest, with the lowest value observed in participants aged 85 years and older (1.8 ± 0.4). On average, muscle thickness decreased by approximately 0.1 cm per decade after age 65. These findings provide age- and sex-specific reference values for quadriceps muscle thickness measured by POCUS, and support its potential utility as a feasible tool for muscle assessment in older adults.