Sedentary people are 20 percent more likely to suffer a stroke than those who regularly break a sweat, according to South Australian researchers. Dr Michelle McDonnell, from the University of South Australia, studied 27,000 Americans aged over 45 who had been involved in a six year study. She found that exercising four times a week at a moderate to intense level was crucial to reducing the chances of a stroke. Strokes occur when the arteries become blocked or burst, preventing blood from flowing to the brain. This limits the amount of oxygen, which can lead to brain damage.