Many fitness instructors give you bad advice when they tell you not to exercise within three hours of going to sleep. The old argument was that vigorous exercise causes your body to produce large amounts of its own stimulants, adrenalin and noradrenalin, that make your heart beat rapidly, raise body temperature and prevent you from feeling tired. More recent research shows that exercising vigorously before going to bed does not interfere with sleep. We also know that exercise helps to prevent disease, prolong life and make you feel good. So it is better to exercise whenever you can, even if it’s just before you go to bed.