Your cardiovascular system consists of your lungs, your heart, your blood and your blood vessels, which are responsible for taking in oxygen, transporting it around your body, removing carbon dioxide and exhaling it. The more efficient your cardiovascular system, the greater your aerobic fitness will be. Your aerobic fitness is expressed as your VO2 max, which refers to the maximum amount of oxygen that you can take in, transport and utilize while exercising. A number of changes occur within your cardiovascular system while you exercise.
Increased Breathing Rate
Chemoreceptors in your blood vessels detect the amount of carbon dioxide in your blood. As levels rise, information is sent from the receptors to your brain and your breathing rate increases. The depth of each breath also increases, and combined with your increased breathing rate, your oxygen consumption can increase by up to tenfold. The normal trigger for breathing is a 4 percent concentration of carbon dioxide in the blood. The more quickly this level is reached, the faster your breathing rate will be.
Increased Gaseous Exchange
Under normal circumstances, i.e. when at rest, you use approximately six liters of oxygen per minute. When exercising, this can increase to up to 60 or more liters per minute, depending on your fitness. As oxygen is inhaled, carbon dioxide is exhaled. This is called gaseous exchange. Gaseous exchange occurs at your alveoli—the air sacs found deep in your lungs. Oxygen diffuses into your blood as carbon dioxide is removed from your blood and exhaled.
Vasodilation
To allow for the increased movement of oxygenated blood around your body, your blood vessels dilate or open up. This occurs in the veins leading toward your heart, your arteries leading away from your heart and your capillaries that interweave your muscles and lungs. You may notice that your blood vessels close to the surface of your skin become bigger while you exercise. This is a good illustration of vasodilation.
Increased Heart Rate
Your heart is a four-chambered muscular pump about the size of your closed fist and located slightly left of center in your chest. Your heart rate is controlled by your own natural pacemaker, called your sinoatrial node, or SAN for short. The SAN will cause your heart to speed up so that oxygenated blood will be pumped around your body more quickly and carbon dioxide-rich blood will be pumped back to your lungs for exhalation. The average resting heart rate is 72 beats per minute, but when exercising strenuously, this may rise to over 200 bpm, depending on your fitness.
References
- "ACSM's Resources for the Personal Trainer"; American College of Sports Medicine; 2009
- "Principles of Anatomy & Physiology, Ninth Edition"; Sandra R. Grabowski & Gerald J. Tortora; 2000
- "Anatomy of Exercise: A Trainer's Inside Guide to Your Workout" Pat Manocchia; 2009
