BALTIMORE — A new study should ease the concerns of many older adults with mild high blood pressure about the strain or harm exercise could cause their hearts. Results of the research on 104 men and women ages 55 to 75 showed that a moderate program of physical exertion had no ill effects on the heart's ability to pump blood nor did it produce a harmful increase in heart size.

In the study, “moderate” translated to sustained exercise for about an hour, three times a week. Researchers say that people's concerns stem from the fact that during each workout, blood pressure can on average rise from 40 millimeters to 60 millimeters of mercury.

The Hopkins study, published in the July issue of the journal Heart, showed that after six months of aerobic exercise on a treadmill, bicycle or stepper, plus weightlifting, participants showed no overall ill effects in 11 measures of diastolic heart function, when the organ's main chamber fills with blood between beats. They also found that exercise produced no increase in eight measures of heart size, including left ventricular mass and wall thickness. In contrast, a long-term effect of hypertension, even when the body is relaxed, is hypertrophy, an enlargement of the heart that eventually stiffens and weakens the muscle.

Not only were there no ill effects sustained, despite periodic increases in blood pressure during the workout, results suggested that the exercise producing these effects benefited the hearts of those who made the most gains in physical fitness and for those who lost the most abdominal fat.

In addition, unlike the increased heart size that results from high blood pressure, any increase in heart size observed in the active group was similar to what athletes experience when their hearts get bigger and stronger, not stiffer, researchers say.

For a six-month period, the Hopkins team assessed the benefits of a supervised program of exercise training in a group of 104 older men and women, measuring heart function, and body fitness and fat levels at the start and end of the study. All of the participants were in generally good health except for untreated, mild hypertension. Half were randomly placed in a widely recommended moderate exercise program while the rest maintained their usual physical routine and diet. The active group participated in a supervised series of exercises for 60 minutes, three times per week.

Aerobic fitness, as measured by peak oxygen uptake on a treadmill, increased by 17 percent as did average strength. The average weight loss in this group was only four pounds, because much of the loss of fat was offset by increased muscle mass. The fat in the abdominal region, measured by magnetic resonance imaging, was reduced by 20 percent among exercisers. The group that was not exercising had either no or significantly less improvement than the exercising group. The Hopkins study's exercise program followed current guidelines from the American College of Sports Medicine.

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