People with blocked arteries may suffer strokes following rigorous exercise, scientists warn today.
New research shows the increased heart rate associated with exercise can be dangerous for people with artery issues.
A specialised computational model was used to simulate blood flow in blocked arteries at three stages of the narrowing; without blockage, with a mild 30 per cent blockage, and with a moderate 50 per cent blockage.
They compared the effect of an exercise-induced heart rate -140 beats per minute - and resting heart rates of 67 and 100 bpm.
And an increased heart rate can induce a stroke in patients with highly blocked carotid arteries, the researchers at the Indian Institute of Technology Kharagpur found.
But for healthy patients and those with only slightly blocked arteries, exercise is beneficial for maintaining healthy blood flow.
The research team explained carotid arteries supply blood flow to facial tissues and the brain and are located on both sides of the neck.
When fat, cholesterol, and other particles build up the inner carotid walls, they form a plaque that narrows the artery.
The narrowing is called stenosis, and while it can be very hard to detect early stages of plaque accumulation, stenosis is dangerous because it limits blood flow to the brain.
Without the necessary blood, the brain lacks oxygen, and the patient suffers a stroke.
In healthy patients, an elevated heart rate increases and stabilises the drag force blood exerts on the vessel wall, reducing stenosis risk.
But for patients already experiencing stenosis, it may not be as beneficial.
As expected, for healthy and mild cases, the exercise condition improved the health of the simulated carotid.
But the team said the results for moderate blockage were "concerning".
Study author Dr Somnath Roy said: "Intense exercise shows adverse effects on patients with moderate or higher stenosis levels.
"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."
Dr Roy said an elevated heart rate could also increase the likelihood of another stenosis forming.
The research team say many factors contribute to stenosis and stroke risk, including age, lifestyle, and genetics, but they recommend checking arterial health regularly for people doing intense workouts.
They also recommend a carefully prescribed exercise regime for people with moderate to severe stenosis or with a history of strokes.
The findings were published in the journal Physics of Fluids.
