The infrahyoid muscles are a group of four paired muscles in the front of the neck that sit below the hyoid bone, the small horseshoe-shaped bone you can feel just above your Adam’s apple. Often called the “strap muscles” because of their long, flat, ribbon-like shape, they work together to pull the hyoid bone and the larynx downward during swallowing, speaking, and breathing. Although they rarely get attention outside anatomy classes and surgical theaters, these muscles play a surprisingly central role in voice production, safe swallowing, and a growing number of reconstructive surgical techniques.
The Four Muscles and How They Are Layered
The infrahyoid muscles are stacked in two layers. The superficial layer, closer to the skin, contains the sternohyoid and the omohyoid. The deep layer, tucked behind them, contains the sternothyroid and the thyrohyoid.1Journal of Ultrasound. Ultrasound anatomy of the neck: The infrahyoid region Each has a slightly different attachment point and a slightly different job, but they operate as a coordinated team.
The sternohyoid is the most superficial strap muscle. It runs from the back of the manubrium (the upper part of the breastbone) and the inner end of the clavicle straight up to the lower border of the hyoid bone. Its primary action is pulling the hyoid downward after it has been lifted during swallowing.
The omohyoid is the oddest-looking of the group. It has two bellies connected by a short intermediate tendon, giving it a zigzag path from the upper border of the scapula (shoulder blade) across the neck to the hyoid bone. That intermediate tendon is tethered to the internal jugular vein by a thin sheet of fascia, which means the muscle actually helps keep that major vein open. When the omohyoid contracts, it tugs on the vein wall and prevents it from collapsing during deep inhalation.2PubMed Central. A study of anatomical variability of the omohyoid muscle and its clinical relevance
The sternothyroid lies deep to the sternohyoid. It runs from the sternum to the oblique line of the thyroid cartilage rather than all the way up to the hyoid, so its main pull is on the larynx itself. The thyrohyoid picks up where the sternothyroid leaves off, bridging the short gap between the thyroid cartilage and the hyoid bone. Together, these two deeper muscles give the larynx an independent range of vertical motion.
Nerve Supply and How the Brain Talks to Them
All four infrahyoid muscles receive their nerve signals through a loop of nerve fibers called the ansa cervicalis. This loop is formed by the front branches of the first three or four cervical spinal nerves (C1 through C3, sometimes C4). One small exception: the thyrohyoid muscle gets its fibers through the hypoglossal nerve rather than the main loop, but the fibers themselves still originate from C1 and C2, just hitchhiking along a different highway to reach their destination.3PubMed. Anatomy of the ansa cervicalis: nerve fiber analysis This shared nerve supply is one reason all four muscles tend to fire together. It also makes the ansa cervicalis a valuable spare-parts nerve in surgical repair, as we will see later.
Blood Supply
The arterial blood feeding the infrahyoid muscles comes from three main sources: the superior thyroid artery from above, the inferior thyroid artery from below, and the internal thoracic artery (also called the internal mammary artery) from behind the sternum. An anatomical study found that the blood supply is segmented, with a dividing line roughly at the level of the cricoid cartilage. Above that line, the superior thyroid artery dominates; below it, the inferior thyroid and internal thoracic arteries take over.4PubMed. Arterial blood supply to the infrahyoid muscles: an anatomical study This segmented pattern means there is no single long artery running the length of the muscle, a detail that matters when surgeons harvest infrahyoid tissue as a flap for reconstruction.
A closer look at the individual vascular pedicles shows that the sternothyroid and sternohyoid muscles each typically receive two separate feeding bundles on each side, one from above and one from below. The superior belly of the omohyoid consistently has one pedicle on each side.5PubMed. Vascular pedicles of infrahyoid muscles: an anatomical study Knowing the exact number and position of these pedicles helps surgeons decide where to cut and where to preserve blood flow.
What They Do During Swallowing
Swallowing is a deceptively complex act that requires the hyoid bone and larynx to move upward and forward, pulling the entrance of the airway shut so food goes down the esophagus instead of the trachea. The suprahyoid muscles (the group above the hyoid) do the heavy lifting during this upward phase. The infrahyoid muscles then haul everything back down once the food has passed, resetting the system for the next breath or the next swallow.
That downward pull is not passive. Research on healthy adults showed that when excessive tension builds in the neck muscles, the infrahyoid group, particularly the sternohyoid, can overpower the upward movement of the hyoid bone. This pushes the hyoid downward at the wrong time, disrupting the normal swallowing sequence.6PubMed Central. Excessive anterior cervical muscle tone affects hyoid bone kinetics during swallowing in healthy individuals In older adults or people recovering from head and neck surgery, this kind of muscle imbalance can contribute to difficulty swallowing, a condition called dysphagia.
The infrahyoid muscles also play a stabilizing role when you open your mouth. They anchor the hyoid bone in place so the suprahyoid muscles can pull the mandible downward without the hyoid moving instead. Without that anchor, opening your jaw would lift your hyoid bone rather than dropping your chin.
Their Role in Voice and Pitch
Singers, speech therapists, and voice scientists pay close attention to the infrahyoid muscles because they help regulate vocal pitch. The basic idea is that these muscles, by pulling down on the hyoid bone and the thyroid cartilage, change the tension and length of the vocal folds inside the larynx. More tension generally means a higher pitch, while less tension lowers it, but the actual biomechanics are more nuanced than that simple model suggests.
An electromyography study of English intonation recorded activity from three strap muscles and found they fired in nearly identical patterns. Their collective activity showed a strong inverse relationship with the geniohyoid, a suprahyoid muscle: when the strap muscles fired more, the geniohyoid fired less, and vice versa. By systematically varying the pitch contours of otherwise identical utterances, the researchers were able to separate the effects of tongue and jaw movement from the activity specifically tied to pitch control. The strap muscles appeared to lower pitch by applying downward force on the hyoid and thyroid cartilage, indirectly altering vocal fold tension.7The Journal of the Acoustical Society of America. The geniohyoid and the role of the strap muscles in pitch control
Opera singers offer an interesting window into how trained voices use these muscles differently. A study comparing professional vocalists to non-singers measured the electrical activity in several external laryngeal muscles during singing tasks like vowel phonation and glissando. The singers showed significantly greater asymmetry in certain neck muscle amplitudes compared to controls, suggesting that years of vocal training reshape how these muscles coordinate.8PubMed. Electromyographic Assessment of the External Laryngeal Muscles of Opera Singers During Phonation and Non-Phonation Tasks Interestingly, this asymmetry was not seen during simple saliva swallowing in either group, reinforcing the idea that voice production demands a more complex and individually adapted motor program than swallowing does.
Anatomical Variations and the Unpredictable Omohyoid
Textbook anatomy describes four clean, symmetrical strap muscles, but the reality is messier. The omohyoid in particular is notorious for variation. A study of 35 cadavers found one case of a doubled omohyoid, three cases where the inferior belly arose from the clavicle instead of the scapula, two cases where the superior belly merged into the sternohyoid, and one case where the omohyoid received extra slips from the sternum.9PubMed Central. A study of anatomical variability of the omohyoid muscle and its clinical relevance
The variability is extensive enough that a recent systematic review proposed a new classification system with two major categories. “Consistency variations” describe changes in the number of muscles present: the omohyoid might be completely absent, might lack its intermediate tendon and appear as a single belly, might have an additional belly, or there might be a whole accessory muscle. “Morphometric variations” describe abnormalities in origin, insertion, or course: arising from the clavicle instead of the scapula, inserting into the sternohyoid instead of the hyoid, running behind the internal jugular vein instead of in front, or having a tendinous rather than fleshy superior belly.10PubMed Central. Anatomical variations of the infrahyoid muscles and ansa cervicalis: a systematic review and an updated classification system for the omohyoid muscle
These variations matter in practice. A surgeon performing a neck dissection expects the omohyoid to sit in a predictable location relative to the internal jugular vein and the carotid sheath. An absent or doubled omohyoid, or one taking an unusual course behind the jugular, can confuse the surgical landscape. Similarly, a radiologist interpreting neck imaging needs to know that an unfamiliar mass in the anterior triangle could simply be a variant muscle belly rather than a tumor.
Why Surgeons Spend So Much Time Thinking About Strap Muscles
The infrahyoid muscles sit directly over the thyroid gland, which means every thyroid operation requires dealing with them. The traditional approach is to retract the strap muscles to the side, preserving them intact. When the thyroid gland is very large, though, surgeons sometimes have to cut through the muscles (transection) to get adequate access. A study comparing patients whose strap muscles were transected during thyroidectomy to those whose muscles were preserved found measurable differences in voice and swallowing outcomes, even when the recurrent laryngeal nerve was left intact in both groups.11PubMed Central. The effect of strap muscle transection on voice and swallowing changes after thyroidectomy in patients without laryngeal nerve injury The finding underscores that the strap muscles themselves contribute to the fine motor control of the larynx, independent of the nerves that control the vocal folds directly.
Infrahyoid Flaps for Oral Reconstruction
Beyond being something surgeons work around, the infrahyoid muscles have become something surgeons work with. The infrahyoid myocutaneous flap, a section of strap muscle harvested along with the overlying skin and kept attached to its blood supply, has been used for decades to repair defects left behind after removing cancers of the tongue, floor of the mouth, and other oral structures. An early case series from the 1980s reported using this flap in over 100 consecutive reconstructions with a 90% success rate, establishing it as a versatile option even for elderly or frail patients.12PubMed. The infrahyoid myocutaneous flap for reconstruction after resection of head and neck cancer
A more recent systematic review and meta-analysis pooling data from over 750 patients across 21 studies confirmed the flap’s reliability. The pooled total flap loss rate was under 2%, with a partial loss rate of roughly 10%. Complications like salivary fistula occurred about 3% of the time, and surgical revision was needed in under 2% of cases. The oral cavity accounted for about three-quarters of reconstructed sites, with the oropharynx making up most of the rest.13PubMed. Infrahyoid myocutaneous flap in head and neck reconstruction: a systematic review and meta-analysis Because the flap is harvested from the same surgical field as the cancer removal, it avoids the need for a second distant donor site on the forearm or thigh, which saves operative time and reduces the overall burden on the patient.14PubMed Central. Infrahyoid Flap, a Convenient Alternative for Reconstruction of Tongue and Floor of Mouth Defects: Case Series
Reinnervation After Vocal Fold Paralysis
When thyroid or other neck surgery damages the recurrent laryngeal nerve, the result is often unilateral vocal fold paralysis: one vocal fold stops moving, leading to a breathy, weak voice and sometimes difficulty swallowing. One established repair strategy uses the ansa cervicalis nerve, the same nerve loop that normally supplies the infrahyoid muscles, and redirects it to the damaged recurrent laryngeal nerve. The idea is not to restore movement to the paralyzed vocal fold but to provide a trickle of nerve signals that maintains muscle tone and bulk, keeping the fold in a good position for the working side to press against it.15PubMed. Timing of Ansa Cervicalis-to-recurrent Laryngeal Nerve Reinnervation: A Systematic Review
A long-term study of 237 patients who underwent this procedure showed significant improvements in glottic closure, vocal fold position, and voice quality after surgery, with the results holding up over time. Postoperative voice measurements showed no meaningful difference from those of a healthy control group, and electromyography confirmed that the transplanted nerve successfully reinnervated the laryngeal muscle.16PubMed Central. Laryngeal Reinneration Using Ansa Cervicalis for Thyroid Surgery-Related Unilateral Vocal Fold Paralysis: A Long-Term Outcome Analysis of 237 Cases Sacrificing the ansa cervicalis to reroute it does mean losing some nerve supply to the strap muscles themselves, but the functional tradeoff is generally well tolerated because the remaining innervation and the other muscles compensate.
Physical Therapy and Postural Connections
The infrahyoid muscles do not exist in isolation. They connect the hyoid bone to the sternum, clavicle, scapula, and thyroid cartilage, which means they are mechanically linked to head posture, shoulder position, and jaw alignment. People with forward-head posture, a common consequence of desk work and screen time, often develop shortened suprahyoid muscles and weakened infrahyoid muscles, which can alter the resting position of the hyoid bone and contribute to jaw and neck discomfort.
Rehabilitation programs targeting this imbalance use exercises designed to strengthen the weakened infrahyoid muscles while stretching the shortened suprahyoid muscles. One approach, sometimes called a digastric facilitation posture exercise, combines correction of mandibular position, tongue posture exercises, and myofascial release. This protocol has been shown to decrease muscle stiffness and improve mouth opening in people with cervical extension posture patterns.17PubMed Central. Effects of combined jaw and cervicoscapular exercises on mouth opening and muscle properties in cervical extension type For people with chronic jaw tension or temporomandibular joint problems, working on the infrahyoid muscles is often part of a broader strategy that also addresses the muscles of the jaw, tongue, and upper back.
Forensic and Trauma Significance
The strap muscles sit in a vulnerable position in the anterior neck, making them susceptible to injury during blunt trauma, strangulation, or hanging. In forensic pathology, hemorrhage within the infrahyoid muscles is one of the soft-tissue findings pathologists look for when evaluating cases of suspected strangulation. Muscle and skin are among the most commonly injured soft-tissue structures in the head and neck during fatal interpersonal strangulation, and the infrahyoid region is a key site of examination during autopsy.
An Evolutionary Perspective
If you zoom out from human anatomy and look at the infrahyoid muscles across the animal kingdom, an interesting pattern emerges. In the evolutionary lineage leading from non-avian dinosaurs to modern birds, the infrahyoid muscles were progressively lost or drastically modified. A study examining the pectoral and infrahyoid musculature across theropod dinosaurs identified the small compsognathids and basal maniraptoriforms as the likely transition points where these muscles began to disappear. The loss of the infrahyoid muscles freed the hyoid apparatus, trachea, and esophagus from being tightly coupled to the shoulder girdle, which may have enabled the complex vocal tract filtering that modern birds use to produce their diverse range of calls and songs.18PubMed Central. The evolution of the pectoral extrinsic appendicular and infrahyoid musculature in theropods and its functional and behavioral importance In a sense, birds traded one set of neck muscles for a more mobile sound-producing apparatus, while mammals kept the strap muscles and evolved a different solution to voice control.
Developmental biology adds another layer to this story. In mammalian embryos, the infrahyoid muscles arise from a complex mix of tissue sources. Research tracking the embryonic origins of neck muscles in mice found that the postcranial extension of a tissue called the cardiopharyngeal mesoderm, lateral to the first three somites, is a likely source of certain neck muscle precursors.19PubMed Central. Unique morphogenetic signatures define mammalian neck muscles and associated connective tissues The neck is one of the last regions of the body whose muscle development has been mapped in detail, partly because its muscles come from so many different embryonic populations rather than from a single neat source. That developmental complexity may help explain why anatomical variations in the strap muscles are so common: when something has to be assembled from multiple embryonic ingredients, there are more opportunities for the recipe to vary.