A previous study reported an increase in carotid-femoral pulse wave velocity (cfPWV) during an upright posture compared to the supine position, partly due to sympathetic activation. However, given that cfPWV is influenced by the transmural pressure (TMP) of the artery, which is elevated in the abdominal aorta in the seated posture due to the increased hydrostatic pressure. Thus, it remains unclear whether this increased cfPWV reflects a true rise in arterial stiffness or is simply a result of the elevated TMP. To assess the validity of cfPWV in the seated posture for arterial stiffness assessment, 20 young healthy subjects underwent arterial stiffness measurements in both the supine and seated positions. There were no significant differences in carotid artery compliance, β-stiffness index, and aortic characteristic impedance between the two positions (