The human foot contains about 20 intrinsic muscles, meaning muscles that both originate and insert entirely within the foot itself. One detailed review places the count at 22 intrinsic muscles, though slight differences in how anatomists classify certain small muscle slips mean you’ll see numbers ranging from 19 to 22 depending on the source.1Churchill Livingstone / ScienceDirect. Intrinsic muscles of the foot: Anatomy, function, rehabilitation On top of those, roughly a dozen extrinsic muscles originate in the lower leg and send long tendons into the foot, giving the foot its pulling power for big movements. That brings the working total to somewhere around 30 muscles acting on each foot, though the exact figure depends on what you count and how you define the boundaries.
Intrinsic Versus Extrinsic Muscles
The reason you’ll find different numbers floating around is that “muscles of the foot” can mean two different things. Intrinsic foot muscles live entirely inside the foot. They handle fine motor control: spreading and curling the toes, stabilizing the arch, and making the subtle adjustments that keep you balanced on uneven ground. Extrinsic foot muscles, by contrast, have their bulky contractile portions up in the calf and shin, with tendons that run down past the ankle to attach to foot bones. These are the muscles responsible for the powerful motions like pointing your foot, pulling it upward, or rolling it inward and outward.
When most anatomy references say “the foot has about 20 muscles,” they mean the intrinsic group. Add in the extrinsic muscles that cross the ankle and insert in the foot, and you get a substantially larger number. But because those extrinsic muscles are shared with the lower leg, they’re often counted as leg muscles rather than foot muscles. That ambiguity is the main reason the internet gives you answers ranging anywhere from 20 to 34.
How the Intrinsic Muscles Are Organized
The sole of the foot is where most of the intrinsic muscles live. Ten plantar intrinsic muscles are arranged in four distinct layers, stacked from the bottom of the foot upward, and grouped into medial, central, and lateral compartments.2PubMed Central. Ultrasound of the plantar foot: a guide for the assessment of plantar intrinsic muscles The shallowest layer, closest to the skin, includes the abductor hallucis along the inner border, the flexor digitorum brevis in the center, and the abductor digiti minimi along the outer edge. Deeper layers contain smaller muscles like the lumbricals, the quadratus plantae, the adductor hallucis, and the interossei. On the top of the foot there is an additional group, the extensor digitorum brevis and extensor hallucis brevis, which help extend the toes independently of the extrinsic extensors coming from the shin.
This layered architecture is not just an anatomical curiosity. Each layer serves a different functional role. The superficial layer provides the broadest stabilization of the arch and toes. The deeper layers handle finer adjustments, like aligning the toes during push-off or distributing pressure evenly across the ball of the foot. Because the muscles are packed tightly into a small space and overlap each other, studying them individually has historically been difficult, which is part of why foot muscles have received far less research attention than, say, the muscles of the shoulder or hip.
What Foot Muscles Actually Do During Walking
For a long time, textbooks described the foot’s arch as a mostly passive structure, held up by ligaments and a thick band of connective tissue on the sole called the plantar aponeurosis. The idea was that the arch worked like a spring: it flattened under load, stored energy, and then snapped back as the toes bent upward. Researchers have challenged that picture significantly. Active muscle contraction, not the passive “windlass” mechanism of the plantar aponeurosis, appears to be the foot’s primary source of stiffness during push-off in walking.3PubMed Central. Foot stiffening during the push-off phase of human walking is linked to active muscle contraction, and not the windlass mechanism The intrinsic muscles actively tense the underside of the foot to create the rigid lever you need to propel yourself forward with each step.
When researchers blocked the nerves supplying the plantar intrinsic muscles, the navicular bone (a key part of the arch) dropped by nearly 4 millimeters, confirming that these muscles actively hold the arch up during standing and movement.4The Journal of Foot and Ankle Surgery. Intrinsic pedal musculature support of the medial longitudinal arch: an electromyography study This might sound like a small number, but in the architecture of the foot, a few millimeters of arch collapse changes how forces travel through the entire lower limb.
The intrinsic and extrinsic muscles also fire in a carefully timed sequence during each stride. During walking, the muscles that flex the toes at the ball of the foot peak in activity before the toe extensors kick in, creating a sequential handoff from the ankle plantarflexors through the toe flexors, then the toe extensors, and finally the ankle dorsiflexors.5PubMed. Coordination of intrinsic and extrinsic foot muscles during walking Disrupting any link in that chain can alter your gait in ways that ripple upward to the knee, hip, and spine.
Not Everyone Has the Same Muscles
The count of about 20 intrinsic muscles is the textbook norm, but real human bodies are less tidy than textbooks. Accessory muscles, essentially extra muscles that most people don’t have, show up in a meaningful fraction of the population. In one anatomical study of 200 specimens, accessory muscles around the ankle were found in about one in eight feet.6Annals of Anatomy – Anatomischer Anzeiger. Accessory muscles around the ankle joint – An anatomical investigation These included extra slips of muscles on the inner, outer, and front of the ankle.
The best-studied accessory muscles are the peroneus quartus and peroneus digiti quinti, which run along the outer ankle. A systematic review pooling data from nearly 4,000 legs found an overall prevalence of about 16% for accessory peroneal muscles, with rates varying by ancestry: the peroneus quartus was more common in Indian populations, while the peroneus digiti quinti was more common in European and American ones.7PubMed. The accessory peroneal (fibular) muscles: peroneus quartus and peroneus digiti quinti. A systematic review and meta-analysis Most people who have these extra muscles never know it. The muscles are usually discovered incidentally on MRI or during surgery. They don’t generally cause problems, though they can occasionally crowd the tendons in the tight space behind the outer ankle bone.
On the developmental side, human embryos briefly possess muscles that disappear before birth. One example is the opponens digiti minimi of the foot, a muscle that would oppose the little toe, much as we oppose our thumb with the hand’s opponens pollicis. This vestigial muscle persists in the embryo until around the 11th week of gestation before shrinking away.8Development. Development of human limb muscles based on whole-mount immunostaining and the links between ontogeny and evolution Its brief appearance is a reminder that our foot muscles carry evolutionary baggage from ancestors whose feet were more hand-like.
Evolutionary Reshaping of Foot Muscles
The shift from tree-climbing to upright walking reshaped the human foot dramatically. We lost the opposable big toe that great apes use to grip branches and gained a longitudinal arch that stiffens the foot for bipedal walking.9PubMed Central. The functional importance of human foot muscles for bipedal locomotion Those structural changes came with muscular ones. Compared to great apes, humans have a distinctively larger quadratus plantae, a deep muscle in the sole that helps redirect the pull of the long toe flexor tendon, allowing more efficient push-off during walking.10PubMed Central. Multivariate analysis of variations in intrinsic foot musculature among hominoids
Among our closest relatives, foot muscle architecture reflects lifestyle. Orangutans, who spend much of their time hanging from branches, have relatively larger interosseous muscles suited for hook-like digital gripping without much use of their rudimentary big toe. Chimpanzees, on the other hand, have proportionally larger muscles around the big toe for hallux-assisted power gripping as they move through trees.11PubMed Central. Muscle dimensions of the foot in the orangutan and the chimpanzee Gorillas stand out with an unusually large abductor digiti minimi, the muscle running along the outer edge of the foot.10PubMed Central. Multivariate analysis of variations in intrinsic foot musculature among hominoids
Humans also gained at least one entirely new muscle in the transition to bipedalism. The fibularis tertius, a small muscle on the front of the ankle that helps lift and evert the foot, is absent in apes and appears to have emerged specifically in the human lineage as an adaptation to upright walking.12PubMed Central. Variant insertion of the fibularis tertius muscle is an evidence of the progressive evolutionary adaptation for the bipedal gait It is present in most people but not all, which is itself a reflection of normal anatomical variation.
When Foot Muscles Weaken or Waste Away
Because intrinsic foot muscles are small and hidden, their deterioration tends to go unnoticed until it causes problems. In runners with chronic plantar fasciitis, the heel-side intrinsic muscles were significantly smaller than in healthy runners, suggesting that muscle atrophy and plantar heel pain are connected, though the direction of cause and effect isn’t entirely clear.13PubMed. Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis A separate systematic review found that people with plantar fasciitis had reduced forefoot muscle size and weaker toe flexor force.14PubMed Central. Relationship between intrinsic foot muscle weakness and pain: a systematic review
Aging takes its own toll. Sarcopenia, the gradual loss of muscle mass that comes with getting older, affects the small foot muscles just as it affects muscles elsewhere in the body. In older adults, both the size and strength of toe flexor muscles decline, which could compromise the ability to walk safely and recover from trips and stumbles.15PubMed. Effects of Age on Strength and Morphology of Toe Flexor Muscles Falls in older adults are a major health concern, and weakened foot muscles may be an underappreciated contributor.
Diabetes adds another layer of complexity. Peripheral neuropathy from diabetes can lead to intrinsic muscle wasting in the foot, and for decades the standard explanation for claw toe deformity in diabetic patients was that weakened intrinsic muscles allowed the extrinsic muscles to overpower them, pulling the toes into a clawed position. That tidy explanation may be too simple. One study found that intrinsic muscle atrophy alone did not discriminate between neuropathic patients who developed claw toes and those who didn’t, suggesting the mechanism is more complex than a straightforward muscle imbalance.16PubMed Central. Role of intrinsic muscle atrophy in the etiology of claw toe deformity in diabetic neuropathy may not be as straightforward as widely believed
Training and Strengthening Foot Muscles
Given the evidence linking intrinsic muscle weakness to foot pain and instability, the practical question is whether you can actually build these muscles up. The answer is yes, though the methods are more specific than just walking more. A training approach commonly called “short foot” exercise, in which you deliberately shorten the foot by drawing the ball of the foot toward the heel without curling the toes, targets the plantar intrinsic muscles and has been shown to improve arch support during functional tasks.17Manual Therapy. Effect of plantar intrinsic muscle training on medial longitudinal arch morphology and dynamic function
A systematic review and meta-analysis of foot core exercises and minimalist footwear found that targeted foot exercises can increase foot strength and may increase the size of some plantar intrinsic muscles. Wearing minimalist shoes during running or daily activities also appears to promote growth of multiple intrinsic foot muscles.18Clinical Biomechanics. The effects of foot core exercises and minimalist footwear on foot muscle sizes, foot strength, and biomechanics: A systematic review and meta-analysis One controlled study found that runners who transitioned to minimalist shoes for a training period developed significantly larger foot muscles, with the growth concentrated in the forefoot region, while runners who kept their conventional shoes showed no change.19Clinical Biomechanics. Effects of training in minimalist shoes on the intrinsic and extrinsic foot muscle volume
Broader reviews of barefoot and minimalist-shoe training in athletic populations also report improvements in intrinsic and extrinsic foot muscle volume, arch function, toe flexor strength, and neuromuscular control.20PubMed Central. Effects of Barefoot and Minimalist Footwear Strength-Oriented Training on Foot Structure and Function in Athletic Populations: A Systematic Review The caveat is that transitioning to minimalist shoes too quickly can increase injury risk, particularly stress fractures in the metatarsals, so any shift should be gradual.
How Specialized Training Reshapes the Foot
Ballet dancers offer a striking example of what years of intense foot use can do to intrinsic muscle size. Compared to non-dancers, ballet dancers had individual plantar intrinsic muscles that were anywhere from 35% to 95% larger relative to body mass. Muscles like the flexor digitorum brevis and the lumbricals, which control toe curling and alignment, showed the most dramatic differences.21PubMed. Differences in the Size of Individual Plantar Intrinsic Foot Muscles Between Ballet Dancers and Non-Dancers Not all muscles grew equally: the abductor digiti minimi and part of the adductor hallucis were proportionally smaller in dancers, reflecting how specific movement demands sculpt the foot’s musculature in different directions. The foot, in other words, adapts to the demands placed on it in a highly targeted way, not as a uniform block of tissue.
Foot Muscles in Reconstructive Surgery
Outside of biomechanics and rehabilitation, foot muscles have a practical role in surgery that most people wouldn’t expect. When a wound on the foot or ankle exposes bone, tendon, or a joint, surgeons sometimes harvest a nearby intrinsic muscle and rotate it into the wound as a living flap to cover the defect. This is simpler, cheaper, and faster to recover from than a free-flap transfer, which involves microsurgically detaching tissue from a distant part of the body and reconnecting its blood supply.
In one series of 34 pedicled muscle flaps used for foot and ankle reconstruction, the abductor digiti minimi was the most commonly used muscle, accounting for more than half of all flaps, followed by the abductor hallucis.22PubMed. The role of intrinsic muscle flaps of the foot for bone coverage in foot and ankle defects in diabetic and nondiabetic patients These muscles are useful flap donors because they are expendable (the foot functions well without one of them), they have a reliable blood supply, and they sit close to common wound sites along the foot’s borders. A systematic review of this approach in diabetic patients found relatively high success rates, though the evidence base remains small and more comparative studies are needed.23PubMed. Use of local intrinsic muscle flaps for diabetic foot and ankle reconstruction: a systematic review
How Researchers Measure These Muscles
One reason foot muscles have been neglected in research for so long is that they are genuinely hard to measure. They are small, tightly layered, and difficult to distinguish from one another using standard imaging. Ultrasound is useful for bedside assessment and has been validated for measuring plantar intrinsic muscle dimensions, but it depends heavily on the skill of the person holding the probe.2PubMed Central. Ultrasound of the plantar foot: a guide for the assessment of plantar intrinsic muscles
MRI provides a more detailed picture and allows researchers to quantify not just muscle volume but also the amount of fat infiltrating the muscle, which is a marker of degeneration. Semi-automated programs can now reliably segment subcutaneous fat, lean muscle, and adipose tissue within the foot from MRI scans.24PubMed Central. Reliability and validity of a MR-based volumetric analysis of the intrinsic foot muscles Higher-field MRI machines, like the 7-Tesla scanners used in research settings, can resolve individual muscles with enough precision that even sampling a limited number of image slices produces measurement errors below 2.5%.25Journal of Biomechanics. Improving the measurement of intrinsic foot muscle morphology and composition from high-field (7T) magnetic resonance imaging These imaging advances are accelerating the pace of foot-muscle research, and the next decade will likely fill in many of the gaps that decades of relative neglect left behind.