During the five years of follow-up, 482 men developed CHD. The data indicate that increased physical activity was associated with a decrease in CHD risk. The researchers found that among men who expended similar amounts of energy in physical activity the duration of the session did not further decrease CHD risk. Further, men who participated in sports or recreational activities did not show lower risks of CHD than those who only reported that they walked or climbed stairs, as long as both groups had similar total energy outputs.

The authors note the possibility that certain factors might have affected the results of the study. For example, the men in the study self-reported the frequency and duration of their physical activities. As a consequence, there is the risk of having them over-report or under-report their activities.

“For those who currently exercise, keep on exercising. But if you cannot do it all at once, then shorter bouts of exercise can add up to still benefit in terms of coronary heart disease,” said Howard D. Sesso, ScD., of Harvard School of Public Health, one of the study’s authors. “For those who are sedentary, try exercising. As long as you are out there doing it, your heart is likely to benefit,” he added.

The authors conclude that “physicians should advise patients to be physically active to decrease their coronary heart disease risk. Physical activity does not have to be arduously long to be beneficial; even short sessions lasting 15 minutes appear to be helpful. This may provide some impetus for sedentary individuals to take up physical activity.”

The American Medical Association notes that exercise can help reduce the risk of getting many diseases. Aside from lowering coronary heart disease risk, other benefits of exercise include: weight loss, which is important for the prevention and control of type 2 diabetes; increase in bone density, which helps prevent osteoporosis; and enhanced emotional well-being, which is associated with a decrease in mental depression.

But while this particular study shows that the accumulation of shorter sessions of exercise had a similar effect on CHD risk compared to one longer session, with respect to total energy expenditure, the researchers did not investigate the association between shorter exercise sessions and their ability to be protective against other diseases.