Here’s some good news: the lower your starting point is in terms of fitness, the less you have to do to see a benefit.

So, if you’re someone who’s completely sedentary, then only a small amount of exercise is needed to see a reduction in cardiac risk. From a starting point of virtually zero exercise, an hour or two a week of leisurely cycling or brisk walking might be all you need to reduce your risk of death from cardiovascular disease by as much as 20%. But as you get fitter and increase the amount you exercise, the cardiovascular health gains diminish and eventually plateau. This is sometimes referred to as a J-shaped curve.

A sedentary person who goes from doing nothing to exercising a couple of hours a week will see the greatest reductions in cardiovascular risk during this period. If they increase the amount they exercise to four hours a week, there would be additional – albeit smaller – reductions in risk (around 10%). But the benefits to cardiovascular health appear to max out after 4-6 hours a week – with no additional gains beyond this point for everyone.

However, one study in which sedentary people were trained to complete an endurance event, such as a marathon, found that once participants reached 7-9 hours a week of training, they saw noticeable changes in their heart’s structure.