A rterial distensibility and its converse stiffness have come of age as physiological concepts 1 and now as a target for intervention. The central hypothesis sustained so far is that an individual's "arterial stiffness" measured as aortic pulse wave velocity (PWV) is a convenient, integrated index of vascular pathology over a person's life course, more precise and reliable than other risk factors individually. For example, blood pressure (BP), whether casual or 24 hour, is more sensitive to stimuli and, therefore, more variable. Arterial distensibility is in part dependent on BP, yet its prognostic power is because of its "independence" from BP, including pulse pressure. 2 It appears to indicate the general burden of atherosclerotic disease and subclinical damage from multiple risk factors over time: the "wear and tear" of constant distension and recoil (part of "aging"), effects of smoking, lipid metabolism, (hyper)glycemia, ethnicity, how family history expresses itself, etc. 3 European hypertension guidelines now include PWV as a recommended but optional measure. The relationship of arterial distensibility with cardiac function and structure, known as aorto-ventricular coupling, is tantalizing because, as a bioengineering feedback loop, cause and effect are still unclear. Many other key questions remain, most critically related to the natural history of arterial stiffness but also fundamental ones of basic structural biology in the vessel wall. A clue to the natural history of arterial stiffness is published in this issue of Hypertension, an Australian study of 9to 10-year-old, generally prepubescent schoolchildren. 4 The study shows a clear relationship among degree of body fat, physical fitness, and arterial stiffness, measured by carotidfemoral PWV. The link of PWV with fitness was not independent of body fat. Why should this article be of interest, being only cross-sectional, whereby association may well not imply cause? The answer is its insight into primary prevention and underlying mechanisms. The study's strengths include its community base, large number of healthy children properly sampled, gold-standard "DXA" assessment of body composition, and an accepted method for PWV measurement. Its weaknesses include PWV measured sequentially rather than simultaneously at carotid and femoral sites over only 8 cardiac cycles. Another is the use of a 20-m shuttle run to assess cardiorespiratory fitness, which can be characterized by a variety of methods that the authors understandably could not apply but do not discuss or compare. Similarly, the pedometer is insensitive for assessing physical activity, especially in children, who may remove it. Perhaps as a result, only 20% of the variance of the PWV measured was related to any of their variables. However, these weaknesses would tend to bias the results toward the null so that any association with PWV was remarkable.