"We think these initial findings are sufficiently positive to encourage a randomized controlled trial that will provide a better test of the independent effects of cardiorespiratory fitness on responses during stress," says lead author Rod K. Dishman, Ph.D.

Dishman and his American colleagues evaluated 13 women with normal blood pressure (average age roughly 25 years). All subjects reported that they exercised either moderately or vigorously at least three times a week during the past year. Participants' fitness levels were determined by measuring oxygen use during stationary biking.

Participants were given three stress tests. First, they performed mental arithmetic by subtracting a two-digit number from a four-digit number without use of a calculator or paper and pencil. In a second test, they placed ice bags on their foreheads for two minutes. In the third test, each participant immersed their right hand in ice water for two minutes. During each test, researchers measured subjects' blood pressure, heart rate, breathing frequency, and blood flow to the calf muscles.

The mental arithmetic test increased both systolic and diastolic blood pressure, as well as blood flow to the calf. The forehead-ice bag test increased blood pressure readings only slightly, but decreased calf blood flow. The hand-ice water test also resulted in increased blood pressure readings, but without any change in calf blood flow.

One of the most interesting findings was that the women who were more fit had less of an increase in systolic blood pressure during the hand-ice water test. Other than that, investigators did not note any effect of fitness level on blood pressure changes during testing.

"The blunted systolic blood pressure response among the fitter women has implications for clarifying the usefulness of the [hand in ice test] as a predictor of future risk of hypertension among women," the authors write. In any future study of the test's value, participants' fitness levels must be further examined, they add.

The findings suggest that physical fitness may be particularly important for women with high levels of stress, psychiatric impairment associated with perceived stress, and those with other risk factors for cardiovascular disease.