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New research suggests that intense exercise could increase stroke risk for people with moderate to severe blocked arteries. Jan Hakan Dahlstrom/Getty Images
  • Researchers are reporting that exercise may induce a stroke in people with highly blocked arteries.
  • Experts say the study is interesting but note the research is based on a computer model.
  • They add that exercise is still beneficial to most people who don’t have blocked arteries.

It turns out that the warnings that usually accompany new exercise programs about consulting with a doctor before starting are there for a reason.

A recent study published in Physics of Fluids suggests exercise could induce stroke in individuals with narrowed or blocked carotid arteries.

Researchers from the Indian Institute of Technology Kharagpur report that an elevated heart rate that typically accompanies exercise can induce a stroke in people with narrowed or highly blocked carotid arteries.

Still, the prevalence of this condition, also known as carotid stenosis, is relatively low, affecting around 3% of the general population.

The study notes that people with moderate to severe artery blockage should approach exercise cautiously, but most people benefit from regular exercise, which is recommended for heart health.

The scientists also said that for healthy people and those with only slightly blocked arteries, exercise is still beneficial for maintaining healthy blood flow.

Carotid arteries located on both sides of the neck supply blood to the brain and facial tissues.

Fat, cholesterol, and other particles building up inside the inner carotid walls can form a plaque that narrows the artery.

That narrowing is called stenosis, which is dangerous because it limits blood flow — and oxygen — to the brain and could cause a stroke. It also can be difficult to detect early in its development.

The elevated heart rate that comes with exercise in a healthy person stabilizes the drag force exerted on the vessel wall, reducing the risk of stenosis.

However, the study’s authors said the effect can be different for people already experiencing stenosis.

The research team used a computer model to simulate blood flow in carotid arteries at three stages of stenosis:

  • without blockage
  • with a mild 30% blockage
  • with a moderate 50% blockage

They then compared those to the effect of an exercise-induced heart rate of 140 beats per minute as well as resting heart rates of 67 and 100 bpm.

As they expected, the exercise condition improved the health of the stimulated carotid for healthy and mild cases. But the results for the moderate blockage were concerning, they said.

“Intense exercise shows adverse effects on patients with moderate or higher stenosis levels,” said study author Dr. Somnath Roy, PhD, an associate professor in mechanical engineering at the Indian Institute of Technology Kharagpur, India, in the statement.

“It substantially increases the shear stress at the stenosis zone, which may cause the stenosis to rupture. This ruptured plaque may then flow to the brain and its blood supply, causing ischemic stroke.”

The research team also said an elevated heart rate could increase the likelihood of another stenosis forming.

Dr. Adi Iyer, a neurosurgeon and interventional neuroradiologist, at Providence Saint John’s Health Center in California, told Medical News Today that doctors have long known higher resting heart rate is correlated with a high stroke risk in people with high blood pressure.

But Iyer said the study’s proposed association with exercise-induced increased heart rate and stroke in people with moderate or severe carotid stenosis is new “and still remains unclear.”

“This study was done using computer modeling, which doesn’t exactly translate to true human physiology. For example, in humans, the brain has a system of collateral circulation called the circle of Willis, which connects the arteries from the left to right and front to back of the brain. The patency of these collaterals as well as numerous other factors will ultimately determine the stroke risk for real patients.”

— Dr. Adi Iyer, neurosurgeon

Iyer noted that the most common signs of a narrowed carotid artery can be “transient weakness or numbness on one side of the face or body, or even temporary vision loss from one eye.”

“When there is a moderate or severe blockage in the carotid artery, patients should seek physicians’ recommendations on lifestyle modifications including exercise regimens,” Iyer said.

“Patients should seek surgical consultations as we now have numerous highly effective and minimally invasive options to open up blocked carotid arteries for patients.”

Ryan Glatt, a certified personal trainer, senior brain health coach, and director of the FitBrain Program at Pacific Neuroscience Institute in Santa Monica, CA, told MNT the study doesn’t account for other factors that can contribute to strokes.

“Inflammation and immune function may play a role in the modulation of weight and metabolism, but it is unclear if this is a causal relationship or correlation. The limitations to these findings are that there are many inflammatory biomarkers and myokines that can be measured, so it is very difficult to get a complete picture of how they all play a role.”

— Ryan Glatt, personal trainer

Glatt added that his biggest takeaway from the study is “exercise can yield anti-inflammatory effects through the up regulation of anti-inflammatory biomarkers and the decrease of pro-inflammatory biomarkers.”

Glatt recommended that people starting a new exercise program “should seek to increase their frequency of exercise.”

“Individuals could also experiment with low, moderate and high intensities of exercise, as there may be unique effects of different intensities on inflammatory biomarkers,” he added.

Dr. Daniel Atkinson, the clinical lead at Treated, an online medical clinic, told MNT that though the study was done via computer model, it demonstrates its theory well, adding more detail to what doctors already know.

“(It) gives us a picture without putting human test subjects through an exercise regime that could be dangerous to them,” Atkinson said. “In real life, people aren’t likely to know how much obstruction they have in their arteries and using variables such as age, activity level and BMI would produce data that’s more ‘translatable’ and gives an indication of real-world risk — but given the risks involved, this isn’t ethical with this type of research. So computer modeling for this type of scenario is the best option available.”

Atkinson added that people need to be aware of what to look for before starting an exercise program.

“The most common early sign is chest pain and you’re more likely to feel this when exerting yourself,” Atkinson said. “Other symptoms include feeling dizzy or nauseous, or shortness of breath.”

“If you’ve not exercised for a while or want to increase the amount of exercise you do, particularly if you have a BMI of over 30, or you’re aged over 40, or if you have a family history of heart disease, it’s best to speak to a doctor for advice first. Exercising regularly is the best way to reduce your risk of heart disease in the long term, but if you’re starting out after a long break, it’s always better to ease yourself in gradually so you don’t put pressure on your heart and arteries.”

— Dr. Daniel Atkinson, physician