Ultrasound imaging (US) is a practical, non-invasive means to measure skeletal muscle architecture. To what extent and how best to use US to identify differences in muscle size between younger and older adults is not fully explored. The purpose was to determine 1) the ability of US to identify differences in quadriceps muscle thickness (MT) between young and older individuals, and 2) the impact of imaging site/anatomical location. B-mode ultrasound (Terason 3300) was used to collect two-dimensional images of the quadriceps of one leg in young (26±4yr, n=8M, 8F) and older (70±7yr, n=7M, 5F) adults. All images were collected from five sites along the anterior (A) and lateral (L) plane of the leg corresponding to 59%, 39%, and 22% femur length. All images were collected with the participant in the supine position. MT analyses (Image J) were performed for the rectus femoris (RF), anterior portion of vastus intermedius (AVI), lateral portion of vastus intermedius (LVI), and vastus lateralis (VL). Older adults had lower MT (P\u3c0.05) for RF (1.64±0.38 vs. 1.33±0.40cm), AVI (1.66±0.28 vs. 1.22±0.45cm), VL (2.11±0.38 vs. 1.54±0.34cm), and LVI (1.78±0.43 vs. 1.16±0.44cm). Specific to each imaging site, differences between younger and older adults were observed at 2/3 sites for VL, 0/2 sites for RF, and 5/5 sites for VI. These data indicate that US is effective for assessing MT, and that US is capable of identifying differences in quadriceps MT between younger and older adults. However, consideration may need to be taken when selecting imaging sites
