Your foot contains more than a dozen named tendons, each connecting a muscle in the lower leg or foot to a specific bone. They fan out across the ankle in distinct corridors: behind the ankle, along the inner side, along the outer side, across the top, and deep within the sole. Together these tendons let you push off the ground, point and flex your toes, stabilize your arch, and keep your balance on uneven surfaces. Understanding where each group sits helps make sense of why certain injuries happen where they do, and why some tendons heal more stubbornly than others.
The Achilles Tendon
The most familiar tendon in the foot is the Achilles, which runs down the back of your lower leg and attaches to the heel bone (calcaneus). It is the largest and strongest tendon in the human body, formed where the tendons of two calf muscles, the gastrocnemius and the soleus, merge into a single cord.1Journal of Orthopaedic Surgery and Research. Morphological variations of the calcaneal tendon: clinical significance You can feel it easily by pinching the back of your ankle just above the heel. Every time you rise onto your toes, push off while walking, or spring into a jump, the Achilles is doing the heavy lifting.
The Achilles is not a uniform rope. Internally it has layers arranged in different patterns that vary from person to person. A small accessory muscle called the plantaris sometimes contributes a thin tendon that runs alongside or merges with the Achilles, and certain plantaris configurations have been linked to a higher chance of developing Achilles tendinopathy.1Journal of Orthopaedic Surgery and Research. Morphological variations of the calcaneal tendon: clinical significance
One reason the Achilles matters so much to locomotion is its role as an energy-recycling spring. When you run, the tendon stretches under load and then snaps back, releasing stored elastic energy. This recoil lets your calf muscles work over shorter length ranges and at slower speeds, cutting down the overall energy cost of movement.2PubMed. More than energy cost: multiple benefits of the long Achilles tendon in human walking and running During distance running, elastic energy return from the Achilles can range from roughly 10 to 70 joules per stride, depending on speed and the individual runner, though the muscle energy cost still exceeds that return.3PubMed Central. Achilles tendon strain energy in distance running: consider the muscle energy cost
Tendons Along the Inner Ankle
On the medial side of the ankle, behind and below the bony bump on the inside (the medial malleolus), three tendons pass through a tunnel held in place by a band of tissue called the flexor retinaculum. The most important of these is the tibialis posterior tendon, which is the largest and most forward-sitting tendon in the medial ankle. It produces plantar flexion (pointing the foot down) and supination (rolling the sole inward), and it plays a critical role in stabilizing your arch.4PubMed Central. The tibialis posterior tendon Think of the tibialis posterior as the main cable holding the arch up from underneath; when it fails, the arch can collapse.
Behind the tibialis posterior, the flexor digitorum longus tendon and the flexor hallucis longus tendon also travel through the medial ankle before diving into the sole to reach the toes. The flexor digitorum longus fans out to the lesser toes (toes two through five), while the flexor hallucis longus heads to the big toe. These two tendons actually cross each other at a junction in the sole called the chiasma plantare, where slips of tendon pass between them. A cadaver study found that in about 95% of feet, a connection runs from the flexor hallucis longus to the flexor digitorum longus, meaning the big-toe tendon shares fibers with the lesser-toe tendon in most people.5PubMed. Anatomical variations of the flexor hallucis longus and flexor digitorum longus in the chiasma plantare This crossover point sits on average about five centimeters below the inner ankle bone.
Tendons on the Top of the Foot
The anterior compartment of the lower leg sends several tendons across the front of the ankle, under a retinaculum that pins them down, and onto the top (dorsal surface) of the foot. These are the tendons responsible for pulling the foot and toes upward.
The tibialis anterior is the most prominent. You can see its tendon stand out on the front of your ankle when you pull your foot toward your shin. It typically attaches to the medial cuneiform bone and the base of the first metatarsal on the inner side of the midfoot.6PubMed Central. Anatomical Variations of the Tibialis Anterior Tendon Insertion: An Updated and Comprehensive Review This tendon is your primary dorsiflexor, the one that keeps the front of your foot from slapping the ground during walking. If it weakens or ruptures, a “foot drop” gait can result.
Running alongside the tibialis anterior are the extensor hallucis longus, which pulls the big toe upward and attaches to the top of its end bone, and the extensor digitorum longus, which splits into four slips for the lesser toes. The extensor hallucis longus originates from the front of the fibula and the membrane between the two shin bones, and its most commonly seen anatomical variant is an extra tendinous slip near the attachment point on the big toe. A smaller muscle called the extensor digitorum brevis lives on top of the foot itself and adds pull to the middle three toes, while a related slip, the extensor hallucis brevis, assists the big toe from the dorsal side.
Tendons Along the Outer Ankle
On the lateral side of the ankle, behind the fibula’s outer bump, two peroneal tendons travel downward into the foot. The peroneus longus takes a long path: it curves under the foot through a groove in the sole’s bones and attaches to the base of the first metatarsal, far across on the medial side. The peroneus brevis takes a shorter route and attaches to the base of the fifth metatarsal, the bony bump you can feel on the outer edge of your midfoot.7PubMed. Insertional anatomy of peroneal brevis and longus tendon – A cadaveric study Together these tendons evert the foot (turn the sole outward) and help stabilize the ankle against inversion sprains.
The peroneal tendons are held in place behind the fibula by bands called the superior and inferior peroneal retinacula. When those bands are damaged, the tendons can slip out of their groove, a condition called peroneal subluxation. Lateral ankle snapping typically results from exactly this scenario.8PubMed Central. Snapping phenomenon around the ankle: An anatomy-based review The peroneus brevis is particularly vulnerable to longitudinal split tears, which can develop when the tendon gets pinched against the sharp posterior edge of the fibula during repeated subluxation.9PubMed Central. Split Peroneus Brevis: An Overlooked Cause of Ankle Dysfunction
A cadaver study also found that almost half of feet showed some variation in where the peroneus brevis inserts, and about a third showed variant insertion of the peroneus longus.7PubMed. Insertional anatomy of peroneal brevis and longus tendon – A cadaveric study These variations are usually harmless, but they matter to a surgeon who needs to know exactly where each tendon ends up.
How the Arch Is Held Together
The foot’s arch is not a rigid structure. It is maintained dynamically by tendons, muscles, and a thick band of connective tissue on the sole called the plantar fascia (or plantar aponeurosis). The plantar fascia attaches at the heel and fans out toward the toes, and it stiffens the foot for push-off through what is sometimes called the windlass mechanism: when your toes bend upward, the fascia tightens and raises the arch. Recent elastography measurements show that in a standing posture, the short toe-flexor muscle (flexor digitorum brevis) plays a more pronounced role in this stiffening than previously appreciated, with stiffness roughly six times greater than in a seated posture.10PubMed Central. Reconsideration of the load-bearing functions of the plantar fascia and intrinsic foot muscles in the windlass mechanism
The foot’s intrinsic muscles and their tendons also contribute elastic energy storage during walking and running. The foot has historically been described as a passive spring, but more recent work demonstrates that it functions partly as an active one, with the small muscles within the foot itself stiffening the arch and recycling energy.11PubMed. Intrinsic foot muscles contribute to elastic energy storage and return in the human foot When researchers blocked the nerves to the intrinsic foot muscles, subjects produced less positive work at the foot during both walking and running, and their propulsive impulse dropped measurably.12PubMed Central. The functional importance of human foot muscles for bipedal locomotion In other words, the short muscles and tendons inside your foot are not just passive passengers; they actively help you push forward with each step.
Why Certain Tendons Are Injury-Prone
Not all foot tendons tear or degenerate at the same rate, and the reason often comes down to blood supply. The Achilles tendon has three vascular territories. Its midsection, the area a few centimeters above the heel, is supplied by the peroneal artery and is markedly more hypovascular than the proximal and distal ends (which are fed by the posterior tibial artery). That poorly supplied midsection is exactly where most Achilles ruptures happen.13PubMed. The arterial anatomy of the Achilles tendon: anatomical study and clinical implications A person whose peroneal artery delivers an especially sparse supply to this zone may carry extra rupture risk.
A similar story plays out in the tibialis posterior tendon. The distribution of blood vessels within it is uneven, and behind the medial malleolus, the blood volume is significantly reduced. Researchers found that the front portion of the tendon in this region is entirely avascular, with no detectable blood vessel lining at all.14PubMed. The blood supply of the posterior tibial tendon This watershed zone is where most tibialis posterior ruptures occur. Limited blood flow means limited healing capacity, which helps explain why posterior tibial tendon dysfunction is so common and so difficult to reverse without intervention.
Posterior tibial tendon dysfunction is a leading cause of adult-acquired flatfoot deformity, a progressive condition where the tendon degenerates and the medial arch gradually collapses.15PubMed. Evolving MR Imaging Applications in Posterior Tibial Tendon Dysfunction: Diagnosis, Surgical Planning, and Postoperative Assessment The condition involves a wide spectrum of ligament and tendon failure and has been linked to demographic factors, medical comorbidities, and genetic processes.16PubMed Central. Adult-Acquired Flatfoot Deformity Early stages may respond to bracing and physical therapy, but advanced cases often require surgical reconstruction. One common surgical strategy involves transferring a nearby tendon, like the flexor digitorum longus, into the tibialis posterior’s insertion point to restore some arch support.
Mechanical Differences Between Tendon Groups
The tendons of the foot do not all share the same material properties. Biomechanical testing shows two distinct behavioral patterns. Tendons working at the inversion and eversion plane (like the tibialis posterior and the peroneals) tolerate higher strain before failure, meaning they stretch further before breaking. Tendons working at the flexion and extension plane (the flexors and extensors of the toes) have higher stiffness and tolerate higher stress, but break at less stretch.17PubMed. Structural and material properties of human foot tendons Put simply, the side-to-side tendons are more elastic, while the up-and-down tendons are stiffer. This makes functional sense: the peroneals and tibialis posterior deal with rolling and balance adjustments that benefit from compliance, while the flexors and extensors need rigid transmission of force for pushing off and lifting the foot.
Anatomical Variations and Accessory Structures
Textbook diagrams make foot tendons look identical from person to person, but in reality, extra tendons and extra bones in or near tendon pathways are common. A case study documented bilateral accessory tendons coming from the tibialis anterior, peroneus tertius, and peroneus brevis muscles, with the accessory tendon lengths ranging from 36 to 104 millimeters and widths from 1 to 3 millimeters, each inserting farther out along the foot than the main tendon.18PubMed Central. Morphological variations and accessory ossicles in the peroneal and tibialis muscles The same individual also had accessory ossicles: an accessory navicular bone (near the tibialis posterior insertion) and an os peroneum (a small bone embedded in the peroneus longus tendon).
These extra structures are usually silent, but they can become a source of pain when irritated. Accessory ossicles in the foot and ankle sometimes mimic fractures on X-rays or cause chronic discomfort that gets misdiagnosed. Awareness of their existence is important because failure to recognize them can lead to unnecessary immobilization or surgery.19PubMed Central. Beyond the obvious: Exploring Os Tibiale Externum and Os Peroneum in Foot and Ankle Pain – A Case Series If you have chronic pain near the inner arch or along the outer edge of the foot that does not respond to typical sprain treatment, an accessory bone rubbing against a tendon is one possibility worth imaging for.
How Aging Changes Foot Tendons
Foot tendons deteriorate with age in specific, measurable ways. Animal research on foot flexor tendons has shown that aging shifts the collagen composition: type I collagen (the strong, organized kind) decreases while type III collagen (thinner, less organized) increases in proportion. At the same time, the expression of genes responsible for tendon maintenance and repair drops significantly in aged tissue.20PubMed Central. Effect of aging on the tendon structure and tendon-associated gene expression in mouse foot flexor tendon The structural scoring of aged tendons also worsened, reflecting greater fiber disorganization and altered cellularity. These changes help explain why tendon problems in the foot become increasingly common after middle age. A tendon that has been quietly losing its repair machinery for decades is more vulnerable to overuse injuries and slower to bounce back from microtrauma.
For older adults, this has practical implications. Gradual tibialis posterior failure leading to flatfoot deformity, Achilles tendinopathy that lingers for months, and peroneal tears that go undiagnosed can all trace back in part to the structural decline happening at the tissue level. Staying active with progressive loading (gradually increasing the demands on the tendon through exercises like calf raises and toe curls) is one of the more effective strategies for maintaining tendon health, because tendons adapt to mechanical stress by remodeling their collagen.
Tendon Transfers in Foot Surgery
When a foot tendon is too damaged to repair directly, surgeons sometimes borrow a tendon from elsewhere in the foot to fill the gap. The flexor hallucis longus is one of the most frequently transferred tendons, often rerouted to replace a failed Achilles or tibialis posterior. The peroneus brevis is another common donor. These transfers work because the donor tendon can take over some of the function of the one it replaces, though not perfectly. The trade-off is donor-site morbidity: the area where the tendon was harvested loses some function, and there is always a risk of nerve or blood vessel injury near the surgical site.21PubMed. Endoscopic Peroneus Longus Transfer for Chronic Achilles Tendon Rupture: A Novel Surgical Technique Newer endoscopic techniques aim to reduce this morbidity by operating through smaller incisions, but tendon transfers remain a significant procedure with a long rehabilitation period.
The feasibility of a tendon transfer depends partly on the anatomy of the individual foot, including which variations and accessory tendons happen to be present. A patient with a robust accessory peroneal tendon might actually have a more expendable donor available, while someone whose flexor hallucis longus shares extensive fiber connections with the flexor digitorum longus at the chiasma plantare might experience more functional compromise from harvesting that tendon. These are the kinds of decisions that make foot and ankle surgery as much about individual anatomy as about textbook technique.