The infrahyoid muscles are four strap muscles that sit below the hyoid bone in the front of the neck. They pull the hyoid down. They are the direct antagonists of the suprahyoid muscles, which pull the hyoid up. The resting position of the hyoid is set by the balance between these two groups.
When the infrahyoid muscles are overactive relative to the suprahyoid muscles, the hyoid sits low. This produces the visible sag and blurred jaw to neck angle that people call a weak jawline.
The four infrahyoid muscles
1. Sternohyoid
A thin strap running from the top of the sternum and clavicle up to the front of the hyoid. Directly pulls the hyoid down toward the collarbone.
2. Sternothyroid
Runs from the top of the sternum to the thyroid cartilage. Depresses the larynx, which indirectly lowers the hyoid.
3. Thyrohyoid
A short muscle between the thyroid cartilage and the hyoid. Lowers the hyoid when the thyroid is fixed, or raises the thyroid when the hyoid is fixed. Bidirectional depending on context.
4. Omohyoid
A unique two bellied muscle with a tendon that runs through a sling attached to the clavicle. The lower belly runs from the scapula, the upper belly to the hyoid. Pulls the hyoid down and to the side.
Together, these four muscles anchor the hyoid to the collarbone and shoulder blade complex. Their pull is a constant downward force.
Suprahyoid vs infrahyoid: the tug of war
The suprahyoid muscles pull the hyoid up toward the jaw. The infrahyoid muscles pull the hyoid down toward the collarbone. The hyoid sits at the point where these two pulls balance.
In an ideal balance the hyoid sits high, the underside of the jaw is taut, and the jaw to neck angle is sharp. In an unbalanced state where the suprahyoid group is weak relative to the infrahyoid group, the hyoid drops. The visible line of the jaw softens.
Modern life shifts this balance in the wrong direction. Suprahyoid muscles atrophy from disuse. Infrahyoid muscles stay reasonably active because they contract during breathing, speaking, and swallowing continuously. The imbalance grows with age.
Why you cannot fix this by weakening the infrahyoid muscles
Some people ask whether they can weaken the muscles pulling the hyoid down as a way to fix the imbalance. The answer is no, and you would not want to.
Infrahyoid muscles have critical jobs: they stabilize the larynx during breathing, they help lower the hyoid during swallowing (to open the esophagus), and they anchor the anterior neck structures. Weakening them would impair swallowing and breathing.
The correct fix is to strengthen the suprahyoid group so it can pull harder against the intact infrahyoid group. That shifts the balance in the right direction without compromising function.
How this connects to HYOIDR
Every training method HYOIDR is built around targets the suprahyoid group specifically. Inspiratory resistance training triggers the airway dilator reflex, which fires the suprahyoid muscles. Repeated daily, they hypertrophy. See the airway dilator reflex article for the mechanism.
Stronger suprahyoid muscles pull harder against the infrahyoid muscles. The hyoid lifts. The jaw to neck angle sharpens. The visible jawline appears. This is the whole reason inspiratory training produces aesthetic changes.
Common questions about hyoid balance
What controls the resting position of the hyoid bone?
The balance of suprahyoid pull (upward) versus infrahyoid pull (downward). Also influenced by posture and tongue position.
What is the difference between suprahyoid and infrahyoid muscles?
Suprahyoid muscles sit above the hyoid and pull it up. Infrahyoid muscles sit below and pull it down. They are antagonists.
Do infrahyoid muscles affect the jawline?
Indirectly. They pull the hyoid down. If they are stronger than the opposing suprahyoid group, the hyoid drops and the jawline softens.
Can you train the infrahyoid muscles?
You can, but you probably should not for aesthetic goals. Stronger infrahyoid muscles would pull the hyoid down harder, worsening jawline appearance.
Which is more important for the jawline, suprahyoid or infrahyoid?
Suprahyoid tone matters more for jawline aesthetics because these are the muscles that lift the underside of the jaw taut. See the suprahyoid muscles article.
Related reading
- The science hub — full index of hyoid, suprahyoid, and infrahyoid articles.
- How to get a better jawline (complete guide) — why muscle balance around the hyoid matters for the visible jawline.
- HYOIDR jawline trainer — the tool that shifts the balance back toward suprahyoid dominance.