Forget creams, lotions and potions, the closest thing we have to an anti-ageing pill is exercise. You may not be able to do anything about your chronological age, but with exercise you can turn back your biological, or "body", age and look and feel years younger. Leading experts on the ageing process agree that while genes play an important role in health, lifestyle factors - for example, nutrition, exercise, stress-management and sleep patterns - account for a full 70 per cent of how well we age. And of all the lifestyle factors, the single most important thing you can do to age healthily is exercise. It causes you to lose weight and preserve a youthful figure. You burn calories and build muscle, which in turn reduces the risks of health hazards such as heart disease, diabetes, certain cancers, high blood pressure and cholesterol. It improves posture, as well as providing you with more energy and stamina. Author Joan Pagano has selected the most effective self- assessment fitness tests to do at home.