Jogging is primarily aerobic exercise. In aerobic metabolism, cells use oxygen to extract energy from fuels such as carbohydrates and fats, producing carbon dioxide as a byproduct. Aerobically working muscles require large amounts of oxygen and produce lots of carbon dioxide. Because the respiratory system, along with the cardiovascular system, is responsible for bringing oxygen to tissues and expelling carbon dioxide, jogging places significant demands on the respiratory system.
The Respiratory System
The respiratory system includes the lungs as well as the airway that brings air into the lungs. Air travels from the throat through the trachea, then through a branching network of tubes, including bronchi and smaller bronchioles, until it reaches clusters of tiny air sacs known as alveoli. The alveoli are surrounded by capillaries. Blood circulating through the capillaries absorbs oxygen from the air you've inhaled and releases carbon dioxide to be expelled when you exhale.
Pulmonary Ventilation
Pulmonary ventilation is a measure of the amount of air moving through the lungs. It is determined by tidal volume, or the volume of air you take in with each breath, as well as breathing rate. Ventilation increases sharply as you begin jogging, then rises gradually until it reaches a plateau. The initial increase is due mostly to greater tidal volume. As you continue jogging, your breathing rate slowly increases as well.
Alveolar Ventilation
A portion of each breath never reaches the alveoli and is not involved in gas exchange. This is air that fills the nose, mouth, throat and the rest of the airway, referred to as anatomical dead space. When you exercise, the bronchioles expand in diameter so air flows more easily. This increases the dead space, but because that increase is much smaller than the increase in tidal volume, a larger proportion of each breath finds its way into the alveoli. Both of these factors increase the efficiency of breathing during exercise.
Control of Ventilation During Exercise
The respiratory centers in the brain stem control ventilation in response to multiple inputs. During exercise, rising levels of carbon dioxide in the bloodstream are an important stimulus. Feedback from contracting muscles also triggers ventilation, as does input from higher motor control areas of the brain. Some joggers may also experience entrainment of the breath. Their breathing rate synchronizes with the rhythmic movement of their limbs as they run.
References
- "Exercise Physiology for Health, Fitness and Performance"; Sharon A. Plowman, et al.; 2011
- "ACSM's Advanced Exercise Physiology"; American College of Sports Medicine; 2006
- "Human Anatomy & Physiology"; Elaine N. Marieb; 1998
