The common instruction to “breathe from the diaphragm” is often used in fields like yoga, singing, and athletics, intending to promote deeper, more efficient respiration. While this advice aims for a beneficial outcome, the literal phrasing is anatomically inaccurate and oversimplifies the complex mechanics of the respiratory system. The diaphragm is indeed the primary muscle of breathing, but it only actively contributes to one part of the breath cycle, and the air itself does not originate from the muscle.
The Diaphragm Is a Muscle of Inhalation
The diaphragm is a large, thin, dome-shaped sheet of skeletal muscle that horizontally separates the chest cavity from the abdominal cavity. Its mechanical role is strictly limited to the intake of air, making it an inspiratory muscle. When the nervous system signals for a breath, the diaphragm contracts and flattens, moving downward toward the abdomen.
This downward movement increases the vertical volume of the chest cavity. Increasing this volume causes the pressure inside the lungs to decrease relative to the outside atmosphere, creating a vacuum effect. This causes air to rush into the lungs passively, which is the process of inhalation. The diaphragm creates the necessary volume change for air to be drawn in, but it does not initiate the movement of air itself.
The diaphragm’s contraction is also aided by the external intercostal muscles, which pull the ribs up and out, further expanding the chest volume. The diaphragm’s active role ceases the moment inhalation is complete.
How Exhalation Works
Under normal, resting conditions, exhalation is largely a passive process that does not require muscle contraction. Once the diaphragm and external intercostal muscles relax, the elasticity of the lungs and the chest wall naturally causes them to recoil. This recoil reduces the volume of the chest cavity, which increases the pressure inside the lungs.
This rise in pressure forces the air out of the respiratory system until the pressure equalizes with the outside atmosphere. The diaphragm returns to its relaxed, dome-shaped position, moving upward into the chest cavity.
The body engages in active exhalation during activities like speaking, singing, exercise, or coughing. This active phase involves the contraction of abdominal muscles, such as the rectus abdominis and obliques. These muscles push the abdominal contents inward and upward against the diaphragm, forcing it higher into the chest cavity to rapidly decrease lung volume.
The Purpose of Diaphragmatic Breathing
The phrase “breathe from the diaphragm” is a shortcut intended to encourage deep, abdominal breathing rather than shallow, apical (chest) breathing. Shallow breathing relies on accessory muscles in the neck and shoulders, leading to tension and inefficient gas exchange.
When the diaphragm contracts and moves downward during inhalation, it displaces the abdominal organs. This displacement causes the abdominal wall to visibly expand outward, making it appear as though the breath originates from the belly. This maximizes the diaphragm’s downward excursion to fully inflate the lower lobes of the lungs.
Focusing on abdominal expansion minimizes movement in the upper chest and shoulders. This technique promotes the use of the body’s most efficient respiratory muscle, leading to a slower, deeper breath that can help reduce stress and lower blood pressure.