Respiratory System Facts

Knowing certain respiratory facts may help you maximize your workouts, get trim, and stay healthy.

The respiratory system functions primarily in the exchange of oxygen and carbon dioxide.

As air passes through the nasal cavities perform three functions to the air:

  • warming
  • humidifying
  • purifying

Air is distributed to the lungs via the:

  • trachea
  • bronchi
  • bronchioles

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There are 23 different generations of bronchioles before the air reaches alveoli where gases are exchanged in respiration.

Expansion and recoil of the lungs controls the amount and movement of air and expired gases in and out of the lungs.

The lungs do not actively expand and recoil themselves but are acted  upon to do so in 2 ways:

  1. Downward and upward movement of the diaphragm to lengthen and shorten the chest cavity.
  2. Elevation and depression of the ribs to increase and decrease the back-to-front diameter of the chest cavity.

Normal, quiet breathing is accomplished almost exclusively by movement of the diaphragm.

During heavy breathing the extra force required is provided by contraction of the abdominal muscles, which push the abdomen upward against the bottom of the diaphragm.

The muscles of inspiration (elevate the rib cage) are the:

  1. external intercostals
  2. sternocleidomastoids
  3. anterior serrati
  4. scaleni

The muscles of expiration (depress the chest) are the:

1. Abdominal muscles:

  •     rectus abdominis
  •     external obliques
  •     internal obliques
  •     transversus abdominis

2. Internal intercostals
Normal plural pressure is normally slightly negative.

Alveolar pressure is the pressure inside the alveoli when the glottis is open and no air is flowing into or out of the lungs. Also, the pressure in all parts of the respiratory tree is the same all the way to the alveoli and is equal to the atmospheric pressure.

During inspiration the pressure in the alveoli must fall slightly below atmospheric pressure. During expiration it must rise above atmospheric pressure.

Durning normal respiration at rest, only 3-5% of the total energy expended by the body is required for pulmonary ventilation.

During very heavy exercise, this can increase to 8-15%.

During breathing, oxygen diffuses from the alveoli into the pulmonary blood and carbon dioxide diffuses from the blood into the alveoli.

At rest, the partial pressure of oxygen in the alveoli is about 60 mmHg greater than that in the pulmonary capillaries. This means that oxygen diffuses into the pulmonary capillary blood and CO2 diffuses in the opposite direction. This all happens instantaneously.

All of the above respiratory facts are well worth studying to appreciate what is taking place during both aerobic and anaerobic exercise. You simply cannot lose belly fat and trim your love handles without a healthy respiratory system.


1. Cross-bridges attach to actin during muscle action.

2. Calcium regulates muscle actions.

3. Acetylcholine acts at the neuromuscular junction to excite the muscle fibers of a motor unit.

4. Type I muscle fibers are the MOST beneficial for a marathon runner.

5. When throwing a baseball, an athlete’s arm is rapidly stretched just prior to throwing the ball. The muscle spindle detects and responds to that stretch by reflexively increasing muscle activity.

6. The heart’s electrical impulse is normally initiated from the SA node.

7. Repolarization of the atrium and depolarization of the ventricle occurs during the QRS complex of a typical ECG.

These notes were taken from and I highly recommend for further study the excellent book,  Essentials of Strength Training and Conditioning.

Here’s an excellent and brief video describing the respiratory system facts: