Being sedentary has several negative health consequences. Your muscles, including your heart and lungs, become weak; your joints become stiff and easily injured; you can develop high blood pressure, fatigue, obesity, osteoporosis, constipation, and increased sensitivity to pain, anxiety and depression. Being physically fit, on the other hand, actually reduces the risk of heart disease, cancer, high blood pressure, diabetes, and other diseases.

The good news is, it's never too late. At any age, at any level of health, even if you already suffer from a chronic disease, you can improve your level of fitness. In fact, according to the U.S. Surgeon General's Report on Physical Activity and Health, women with heart disease or arthritis actually experienced improved daily function due to involvement in various modes of physical activity.

What, exactly, is fitness? Physical fitness has four components:

Cardiovascular fitness: Your heart, lungs and blood all need oxygen to work. Your level of cardiovascular fitness will determine your body's ability to use oxygen as a source of energy. It gives you the stamina or endurance to be active without gasping for breath.

Muscular strength and endurance: This is the force your muscles can exert and their ability to keep moving without becoming exhausted.

Flexibility: Flexibility helps to maintain the optimal range of motion in the joint areas, making bending and stretching easy.