Cardiovascular fitness is improved by aerobic exercise. The word aerobic refers to something that occurs in the presence of oxygen. Aerobic exercise improves cardiovascular health as it typically uses the body's largest groups of muscles (the legs) continually which makes a person need more oxygen. The more oxygen a person needs, the more efficiently his or her cardiovascular system must be functioning. Examples of aerobic exercise include running, walking fast, biking, and dancing. Incorporating cardiovascular, or aerobic, activity strengthens the heart and lungs. This makes it easier to do all sorts of everyday activities, such as hurrying to class, climbing stairs, or mowing the lawn.