Exercising four to five times a week is necessary to stop the main arteries to the heart from stiffening up, research suggests. 

Two or three exercise sessions a week kept only some arteries healthy, a study of 100 people in their 60s found.

The researchers said any form of exercise reduced the risk of heart problems.

But the right amount of exercise at the right time in life could reverse the ageing of the heart and blood vessels.

The study, published in The Journal of Physiology, looked at participants' exercise history throughout their lives and measured the stiffness of their arteries.

Arteries are blood vessels which transport blood in and out of the heart and to all parts of the body.

Each one is shaped like a tube and as people age, they are prone to stiffening. An unhealthy lifestyle also causes the arteries to become blocked with fatty material.