Many people do cardio to burn calories for weight loss, and it is great for that. Others want to improve sports performance. Cardio also does that. The main purpose of cardiovascular exercise, however, is to improve the function of your heart and lungs to reduce your risk of diseases such as diabetes and heart disease. Your heart and lungs muscles are the main target for cardiovascular exercise. The large muscles in the rest of your body, including legs and arms, are secondary targets.
All cardio workouts depend on the heart and lungs to send oxygen-rich blood to the working muscles so they can keep going. As you perform aerobic activity, repeated signals are sent to your heart to pump faster to supply more blood to the muscles being used. These repeated muscular heart contractions strengthen the heart muscle so that it can pump more efficiently. When you cool down by walking slowly after a run, for example, your heart slows down also, because your legs don't need as much oxygen. Over time, your heart does not work as hard overall, because it has gotten stronger.
Your lungs are organs that are directly above the diaphragm, a muscle that expands and contracts to allow the lungs to take in and release air. During cardiovascular exercise your lungs work in conjunction with your heart to supply oxygen-rich blood to the muscles. As your heart rate increases, so does your breathing rate. Through regular cardiovascular exercise, your lungs become more efficient at exchanging oxygen for carbon dioxide, so you'll find that you don't breathe as heavily during workouts.
In most forms of cardio, the legs are getting a workout, too. These large muscle groups demand more oxygen when working. Walking, running, cycling, elliptical, step machines and even most group exercise classes require your legs to work to raise your heart rate. As the muscles become more efficient at exchanging carbon dioxide for oxygen, endurance improves. Some classes and activities also involve the upper body, and over time these muscles will also get stronger.
Cardiovascular Exercise Recommendations
The American College of Sports Medicine recommends an accumulation at least 150 minutes of cardiovascular exercise each week. You can spread this out over three to five days per week to make it more manageable. However, it can be performed every day for increased benefit. You can choose whatever activities that you enjoy and challenge you, but keep your intensity moderate to vigorous. If you are at a normal body weight, exercise for 20 to 30 minutes per session. If you are looking to lose weight or maintain weight loss, exercise for 30 to 60 minutes.