Highly active middle-aged subjects appear to avoid the arterial stiffening that typically comes with aging, UPI quoted U.S. researchers as saying. Maleah Holland, a graduate student in the Counsilman Center at Indiana University Bloomington, said the reduction in compliance of the body's large arteries has been shown to occur with age and with inactivity, and is considered a risk factor for cardiovascular disease. The researchers compared the arterial compliance of highly active swimmers with that of people who reported being only moderately active or completely inactive. The study found the difference between the highly active participants and the others was significant. The study involved 21 men and 28 women. The 33 highly active subjects were U.S. Master Swimmers who reported more than 200 minutes of vigorous activity a week. For comparison purposes, jogging would be considered a moderate level of activity, while interval training, which combines shorter but more intense periods of running with rest, would be considered vigorous activity, Holland said.