Background It is commonly acknowledged that the ability to use the ankle–brachial index (ABI), a reliable way to diagnose atherosclerosis, decreases with age in the general population. The aim of this study was to determine the relationship between resting ABI and age in different populations.

Methods 674 physically active participants with (active high risk, ACT_HR) or without (active low risk, ACT_LR) cardiovascular risk factors or/and sedentary (SED) subjects, aged 20–70 years. Systolic arterial pressure was recorded at rest and simultaneously with automatic sphygmomanometers at the arms and ankles. ABI was calculated as the ratio of the lowest, highest or mean ankle pressure to the highest arm pressure.

Results Proportion of ABI_min<0.90 was 10.3% in SED_HR subjects versus 0.5% and 1.2%, respectively, in ACT_HR and ACT_LR groups. The averaged ABI value of each group was in the normal range in all groups (ABI>0.90) but was significantly lower in SED_HR compared with all active participants (p<0.001). Regression lines from ABI_mean versus age could lead to approximately +0.05 every 15 years of age in apparently healthy active participants (ACT_LR).

Conclusion ABI at rest increases with the increase in age in the groups of low-risk asymptomatic middle-aged trained adults. The previously reported decrease in ABI with age is found only in SED_HR subjects, and is very likely to rely on the increased prevalence of asymptomatic arterial disease in this group. The increase of ABI with age is consistent with the ‘physiological’ stiffness observed in ageing arteries even in the absence of ‘pathological’ atherosclerotic lesions.

Trial registration number NIH clinicaltrial.gov: NCT01812343.