Probably because exercise increases the body’s metabolic rate – which is, in essence, it’s ability to turn food into energy. One session of exercise can do this for up to 48 hours. So exercising 3 times a week keeps your inner ‘fire’ burning, which you experience as energy. Aerobic exercise (such as running, dancing or swimming, but not working with weights) also makes you breathe more deeply, which, provided you don’t overdo it, oxygenates the body. Some forms of exercise also loosen up the body to allow ‘vital energy’, also known as chi or ki in the Far East and prana in India, to flow more freely. This further increases your available energy. The best form of exercise for this are yoga & t’ai chi.
Article taken from 500 Health & Nutrition Questions Answered – by Patrick Holford.