Want to stay young for long? If so, start exercising four to five times a day as it may help keep your heart stay healthy and slow down ageing, according to researchers. Research showed that different sizes of arteries are affected differently by varying amounts of exercise. While exercising for about two to three days a week for about 30 minutes may be sufficient to minimise stiffening of middle-sized arteries, exercising for about four to five days a week is required to keep the larger central arteries youthful. The study would help "develop exercise programmes to keep the heart youthful and even turn back time on older hearts and blood vessels", said one of the study authors, Benjamin Levine from the University of Texas. With age, arteries - which transport blood in and out of the heart - become prone to stiffening, increasing the risk of heart diseases. For the study, published in The Journal of Physiology, the team examined 102 people over 60 years old, with a consistent lifelong exercise history. The participants were divided into four groups depending on their exercise history - Sedentary: less than 2 exercise sessions per week; Casual Exercisers: 2-3 exercise sessions per week; Committed Exercisers: 4-5 exercise sessions per week and Masters Athletes: 6-7 exercise sessions per week. A lifelong history of casual exercise (two-three times a week) resulted in more youthful middle-sized arteries, which supply oxygenated blood to the head and neck. However, committed exercisers (4-5 times per week) also had more youthful large central arteries, which provide blood to the chest and abdomen, in addition to healthier middle-sized ones. Larger arteries need more frequent exercise to slow down ageing, the researchers said. The findings will help see "if we can reverse the ageing of a heart and blood vessels by using the right amount of exercise at the right time", Levine explained.