Swimming exercise is recommended as a modality of aerobic exercise by worldwide organizations, although a relative paucity of studies has described the effects of swimming on vascular risk factors in healthy populations. Recently, Nualnim et al reported increased carotid artery compliance after a 3-month swimming training intervention in previously sedentary older adults. Previously, the same team had provided evidence for higher carotid compliance in swimmers and runners trained long term compared with sedentary older adults. On the basis of these findings, Nualnim et al suggested that regular swimming might be a highly suitable exercise alternative to land-based exercise to prevent arterial stiffness. Given the relevance of that statement for the exercise prescription in the prevention of arterial disease, I would like to contribute to the discussion.

Studies of long-term swim- or land-based trained subjects, performed by different research teams, have shown conflicting results in arterial compliance. In contrast to the findings from Nualnim et al, a previous study in young adults demonstrated higher carotid compliance in a group of cyclists compared with swimmers and sedentary controls, with no difference between the latter 2 groups. Likewise, higher peripheral arterial compliance was observed in the predominantly trained limbs of cyclists, but not in those of swimmers, compared with sedentary controls. In keeping with these findings, Nualnim et al found that the brachial-ankle pulse wave velocity, an integrated index of central and peripheral arterial stiffness, was significantly reduced in runners compared with swimmers and sedentary controls, again showing similar values between swimmers and controls. Furthermore, the aforementioned 3-month swimming training intervention did not modify peripheral arterial stiffness in sedentary older adults. Taking these findings together, I believe it is questionable to consider swimming exercise as an equivalent alternative to land-based exercise to prevent arterial stiffness as previously implied. Nonetheless, I do not dispute that swimming training might have beneficial effects on some variables related to arterial compliance compared with sedentary status in older adults. It was interesting to note, however, the higher peripheral arterial stiffness noted in the upper limb of long-term swim-trained prepubertal children compared with their sedentary counterparts, suggesting a deleterious effect of swimming training on arterial stiffness in immature populations.

In conclusion, few research groups and, thus, few studies have investigated the effects of swimming exercise on arterial stiffness. Therefore, until more evidence becomes available, I suggest keeping this interesting and consequential question open to further discussion.