Background: Greater muscular strength (MusS) has been found to have an inverse association with subclinical atherosclerosis in children, as well as with mortality from cardiovascular diseases (CVDs) in middle-aged and elderly individuals. However, the association of the degree of MusS with atherosclerosis may differ by sex and has not been clarified in young adults. Methods and Results: A total of 1021 Taiwanese military personnel, aged 18−40 years, participated in annual health examinations in 2018−2020. MusS was separately assessed by 2-min push-up and 2-min sit-up numbers. Subclinical atherosclerosis was measured by the left carotid bulb intima−media thickness (cIMT) using high-resolution ultrasonography. Multiple linear regression with adjustments for age, sex, alcohol intake, cigarette smoking, anthropometric indices, blood pressure, and lipid profiles was utilized to determine the correlation between MusS and cIMT. Both 2-min push-up and 2-min sit-up numbers were inversely correlated with cIMT (standardized β: −0.089 and −0.072, respectively; both p-values < 0.05). In men, both 2-min push-up and 2-min sit-up numbers were inversely correlated with cIMT (standardized β: −0.076 and −0.086, respectively; both p-values < 0.05), while in women, 2-min push-up numbers but not 2-min sit-up numbers were inversely correlated with cIMT (standardized β: −0.204 and −0.01; p = 0.03 and 0.99, respectively). Conclusions: Among young adults, there was an inverse association between MusS and cIMT, emphasizing the beneficial impact of MusS on the regression of atherosclerosis. The study also revealed a sex difference and suggested that training of the upper arm muscles may be an effective preventive measure for young women to reduce the risk of early cardiovascular diseases.