Can too much exercise cause a stroke?
BBC presenter Andrew Marr blames his recent stroke on overworking and an overly vigorous exercise session on a rowing machine.
The 53-year-old said he had, to his detriment, believed the newspapers... that we must take very, very intensive exercise in short bursts for good health.
So should we now leave high-intensity training to only the youngest and fittest people?
People of all ages can have a stroke, although they occur most commonly in people who are older.
More than 150,000 people in the UK have a stroke each year and a quarter of them are under 65.
Most of the time there will be underlying health problems like having high blood pressure.
And there are simple lifestyle changes that you can make to reduce your risk of stroke.
These include keeping fit by doing regular exercise, maintaining a healthy weight, refraining from smoking and making sure you don't drink too much alcohol.
Doctors say that regular exercise can halve your risk of stroke.
About 30 minutes of activity five days a week is enough. And you do not have to do it all in one go - it is just as effective to exercise a few times a day in 10, 15 or 20-minute sessions.
But in terms of intensity, erring on the side of caution might be best.
Know your limits
Advocates of high-intensity interval training say doing a few short bursts of exercise each week - four 30-second sprints on an exercise bike, for example - is a good way to keep fit.
The idea is that pushing your body to its limit gives you a better workout.
Studies suggest that high-intensity interval training causes significant changes in a number of important health parameters, and more so than hours of conventional exercise.
It can boost aerobic fitness, as well as improve how the body's metabolic processes.
BBC presenter Dr Michael Mosley gave it a try himself and found some benefits.
But he does point out that high-intensity training will not suit everyone.
And, like any new exercise regime, if you have a pre-existing medical condition you should consult your doctor before trying it.
The Stroke Association also advise caution. They say it is important to find a balance between how hard the exercise is, how long you exercise for and how often you exercise.
You will benefit more from doing regular gentle exercise for a good length of time, than exercising very vigorously for a short length of time or infrequently, they say.
Nikki Hill, director of communications, said: "Regular exercise is an important factor in stroke prevention and recovery.
"We have heard anecdotally that some activities like vigorous exercise can sometimes cause blood vessels to burst.
"We need more research on the underlying factors that might make that happen. We do know that high blood pressure itself is the single biggest cause of stroke, until more research is done on specific triggers we'd suggest getting your blood pressure checked and taking steps to keep it under control, exercise can help with that."
There can be warning signs that a stroke is likely.
Andrew Marr says he had two minor strokes in the year before his major one, but had not noticed.
Many strokes are preceded by mini ones called transient ischaemic attacks or TIAs.
These may be silent or cause only a few of the symptoms that come with a full-blown stroke - such as face or arm weakness and speech problems - and last just a few minutes, making them easy to miss.
A TIA is a sign that part of your brain is not getting enough blood and you are at risk of having a stroke in the future.
Each year about 46,000 people in the UK have their first TIA.
There is no way of telling whether you are having a TIA or a stroke when the symptoms first start. If you think you or someone you know is having a TIA, it is a medical emergency so call 999.