To Maintain Aerobic Fitness, you have to set fitness goals for yourself every month. Besides, walk for twenty to thirty minutes each day. In addition, drink at least eight 8-ounce glasses of water each day to keep your body hydrated. Other than that, lead an active life when you are not exercising. Moreover, take a daily multivitamin to support your body’s nutritional needs and supplement your body with the nutrients you do not receive from your regular diet.