The flexor hallucis longus lies deep to the gastrocnemius and soleus and lateral to the tibialis posterior. The muscle belly anchors to the posterior surface of the fibula before joining the tibialis posterior and flexor digitorum longus distally, just behind the medial malleolus. 

These muscles all traverse the tarsal tunnel, a channel formed between a depression in the medial calcaneus and the fibrous flexor retinaculum. This structure is similar in architecture and function to the carpal tunnel of the hand. The tarsal tunnel also contains the tibial artery and nerve. It is helpful to use “Tom, Dick, ANd Harry” to remember the Tibialis posterior, flexor Digitorum longus, tibial Artery and Nerve, and flexor Hallucis longus. 

The flexor hallucis longus, flexor digitorum longus, and tibialis posterior all invert the foot and plantarflex the ankle. The flexor hallucis longus also flexes the big toe at the metatarsophalangeal and interphalangeal joints. This motion is critical for push off during gait and propulsion of the body. Center of gravity shifts from the heel, across the foot, and onto the big toe at the end of the stance phase of gait. Forces generated by the hip, thigh, knee, and lower leg move through the foot and big toe, propelling the body forward; the flexor hallucis longus plays a significant role in directing those forces.

In addition to its role in propulsion, the flexor hallucis longus is one of several muscles that dynamically stabilizes the medial arch of the foot. It joins the other muscles of the tarsal tunnel and intrinsic muscles of the foot to control pronation during weight-bearing activities like walking, running, and jumping. The flexor hallucis longus conforms the foot to whatever surface it contacts and also helps make balance adjustments. Dysfunctional posture of the medial arch, insufficient arch support, and weakness or instability of the ankle and foot can create pain, numbness, and poor force transfer in the lower extremity. 

Flexor Hallucis Longus

Attachments

•
Origin: Distal posterior surface of the fibula and interosseous membrane

•
Insertion: Base of the first distal phalanx, plantar surface

Actions

•
Flexes the first metatarsophalangeal and interphalangeal joint

•
Plantarflexes the ankle

•
Inverts the foot

Innervation

• Tibial nerve

• S2–3

Palpating the Flexor Hallucis Longus

Positioning: client prone.

1.
Standing at the client’s feet, locate the medial malleolus
with your thumb.

2.
Slide your thumb posteriorly and superiorly into the space between the malleolus and Achilles tendon, and onto the three tendons located there. (Caution: The tibial artery and nerve also run posterior to the medial malleolus. Be sure to reposition your thumb if the client reports numbness or tingling, or if you feel a pulse.)  

3.
Continue to palpate the most posterior tendon, which is the flexor hallucis longus.

4.

Resist as the client flexes the big toe to ensure proper location.

Client Homework—
Seated Toe Stretch

1.
Sit on the floor with your leg straight out in front of you.

2.

With a relaxed knee, bend at your waist and lean forward.

3.
Grasp your big toe with your fingers.

4.
Gently pull the big toe back toward your knee until you feel a slight stretch.

Editor’s note: The Client Homework element in Functional Anatomy is intended as a take-home resource for clients experiencing issues with the profiled muscle. The stretches identified in Functional Anatomy should not be performed within massage sessions or progressed by massage therapists, in order to comply with state laws and maintain scope of practice.