Exercise is generally recommended as one of the top forms of prevention for heart disease, the leading cause of death in the U.S. and globally. Apart from helping to maintain a healthy weight, physical activity plays important roles in reducing and delaying the development of high blood pressure, lowering cholesterol levels and preventing type 2 diabetes.
But in some people who have already encountered heart problems, intense exercise may increase the risk of having a stroke, new research shows.
A study published this month in the journal Physics of Fluid suggests that when vigorous exercise increases heart rate, people with blocked or narrowed arteries can aggravate their conditions and potentially harm the brain.
Researchers used computer models to look at the effects of intense exercise on people with carotid artery stenosis, a disease that affects about 16.5 million Americans. The carotid arteries run along either side of the neck and act as the blood supply for the brain and face. These arteries can become clogged with plaque as people age, particularly among those who are overweight, smoke and have other issues like high blood pressure and high cholesterol.
The study looked at blood flow in the carotid arteries using simulations of different stages of stenosis, comparing the effects of rapid heart rate to resting heart rate. One model included no artery blockage, another had mild blockage of 30% and a third had moderate blockage of 50%.
When there was no blockage or only mild blockage, the researchers found that a rapid heart rate from intense exercise benefitted carotid artery health — consistent with the general view that exercise would be helpful.
But in the model using 50% blockage, intense exercise put stress on the plaque-filled areas of the artery walls. This can cause the plaque in the artery to burst, which could then be sent to the brain’s smaller blood vessels and cause a stroke.
The authors of the study noted that their findings are not based on clinical tests, but point to possible stressors that may impact people with various forms of heart disease. The study also is limited in its grasp of how long an elevated heart rate must be sustained in order to pose risks to the brain, since different kinds of exercise have varied effects on the heart and blood flow.
Future models will look into the effects of high heart rate on other arteries to better understand when certain kinds of exercise may do more harm than good.
The study should not discourage people from getting regular exercise, but should instead guide them to consider which types of activity are best suited to them if they already have blocked arteries, the authors told Healthline. Low-impact exercises include walking, yoga and Tai chi. At the gym, an elliptical or stationary bike can be used at a comfortable pace.
Nearly 800,000 people in the U.S. have strokes each year, the vast majority of them due to compromised blood flow to the brain. Although stroke prevention improved significantly during the second half of the 20th century, that progress has stalled in many demographic groups over the last decade. The issue has drawn more attention from health researchers due to an anticipated increase in the risk of fatal strokes among millennials as they age.