Whether an exercise enthusiast or a sedentary individual, your aerobic fitness declines during prolonged periods of inactivity. In fact, superior cardiovascular health -- earned through physical activity -- requires weekly exercise for maintenance. Additionally, an inactive lifestyle expedites physical decline due to aging. Understanding the impact of inactivity on aerobic fitness enables informed exercise decisions.
Oxygen Uptake
Oxygen uptake defines your ability to take in and use oxygen during physical activity. Inactivity lowers the amount of air you can inhale during a single breath, weakens your breathing muscles and minimizes alveolar function. Small sacs located within your lungs, alveoli exchange oxygen for carbon dioxide in circulating blood. Maximal oxygen consumption, the greatest amount of air you can process during physical activity, can decrease up to 30 percent between the ages of 20 and 65. However, weekly aerobic exercise can maintain high maximal oxygen consumption throughout life.
Cardiac Output and Stroke Volume
Stroke volume measures the amount of blood pumped through a heart chamber during a single heart beat, and cardiac output represents the volume of blood pumped from your heart per minute. Inactivity reduces the size and strength of your heart and decreases both factors of aerobic fitness. With minimized cardiac output and stroke volume, your heart must beat faster for adequate blood flow during physical activity.
Capillary Density
The smallest blood vessels of all, capillaries remove metabolic waste -- such as harmful carbon dioxide -- and deliver oxygen to working muscles. While physical activity increases the amount of capillaries within each muscle, inactivity lowers capillary density, or amount, throughout your body. Fewer capillaries expedite muscle fatigue and reduce your aerobic fitness.
Mitochondrial Density
Mitochondria reside within muscle cells and use oxygen for energy formation. Like capillary density, mitochondrial density increases with exercise and decreases with inactivity. Aerobic fitness depends on mitochondria for fuel creation during activities like running, hiking and cycling. As inactivity reduces mitochondrial density, aerobic fitness declines.
Blood Volume
Exercise increases your blood volume with enhanced red-blood-cell and blood-plasma volume. Plasma aids in temperature regulation while red blood cells transport oxygen through your blood stream. Additionally, increased blood volume supports an increased cardiac output and stroke volume. However, enhanced blood volume, and associated benefits, decrease within one week of inactivity. Therefore, weekly exercise provides numerous benefits for your level of aerobic fitness. As always, consult a doctor before starting an exercise program.
References
- "Exercise Physiology: Human Bioenergetics and Its Applications"; George A. Brooks, et al.; 2004
- "ACE Personal Trainer Manual"; American Council on Exercise; 2003
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