But it takes around two years of regular intense exercise to reverse the bad effects of a sedentary life, say researchers from the Institute for Exercise and Environmental Medicine in Dallas, Texas.
"The key to a healthier heart in middle age is the right dose of exercise at the right time in life. We found what we believe to be the optimal dose of the right kind of exercise, which is four to five times a week, and the 'sweet spot' in time, when the heart risk from a lifetime of sedentary behaviour can be improved," said study leader Dr Benjamin Levine.
That sweet spot is around the age of 53, the researchers discovered, after they monitored the hearts of a group of 61 middle-aged healthy, but sedentary, people. Half started regular exercise, while the rest carried on with their normal lives.
The exercise group's introduction to a more active life was gradual, beginning with three 30-minute spells of moderate exercise every week for the first three months before embarking on one session a week of high-intensity aerobic exercise, and two to three days of moderate exercise, where the person sweats but can still hold a conversation.
At the end of the two years, the hearts of the exercise group had an 18 per cent improved capacity for oxygen intake, and a 25 per cent increase in the flexibility or 'plasticity' in the left ventricular muscle of the heart, both key markers of a healthy heart.