How Toe Flexor Muscles Support Balance, Gait, and Arch Health

Toe flexor muscles are among the hardest-working structures in your foot, yet they rarely get the attention devoted to bigger muscle groups. These muscles, both the small intrinsic ones housed entirely within the foot and the longer extrinsic ones running down from the lower leg, do far more than curl your toes. They stiffen the arch under load, help drive you forward during walking and running, and feed your brain a constant stream of sensory information about where your body sits in space. Their strength, or lack of it, shows up in conditions ranging from plantar fasciitis to falls in older adults.

What the Toe Flexors Actually Are

Your foot contains two broad families of toe flexor muscles. The intrinsic flexors live entirely inside the foot. The main players include the flexor digitorum brevis, which runs along the sole and bends the four smaller toes; the flexor hallucis brevis, which bends the big toe at its base joint; the abductor hallucis, which both flexes and pulls the big toe inward; and the quadratus plantae, a deeper muscle that helps redirect pulling forces from the long tendons above. The extrinsic flexors originate higher up in the calf. The flexor hallucis longus runs behind the ankle and all the way to the tip of the big toe, while the flexor digitorum longus branches into tendons serving the four lesser toes. Together, these muscles form a layered system that can grip the ground, stabilize the arch, and generate the push-off force you need for every step.

Ultrasound studies confirm that the size of these muscles tracks closely with the force they produce. In young adults, the cross-sectional area and volume of the flexor digitorum brevis correlate strongly with toe flexor strength, and the abductor hallucis shows a similar relationship with big-toe force measured during standing.

How They Support Standing and the Foot Arch

Standing upright sounds passive, but the toe flexors are anything but idle. Research measuring maximum isometric toe flexor strength found it was significantly higher when participants stood compared to when they sat, suggesting that bearing your own body weight amplifies the muscles’ force-generating capacity. This amplification appears to be linked to the foot arch itself: as the arch flattens slightly under load, it stretches the muscle-tendon complex along the sole, essentially pre-loading the toe flexors so they can produce more force. People with more flexible arches showed a greater increase in toe flexor strength from sitting to standing than those with stiffer arches, pointing to an elegant feedback loop between arch shape and muscle output.¹

A follow-up investigation into the mechanical drivers of this strength identified the flexor hallucis brevis and abductor hallucis as the primary determinants of toe flexor strength during standing. When the researchers accounted for body weight, the quadratus plantae, arch height, and arch stiffness all factored in, reinforcing the idea that toe flexor output is not just about raw muscle size but about how the whole foot structure responds to load.²

Exercises targeting the intrinsic flexors also appear to help maintain the medial longitudinal arch, the main weight-bearing arch running along the inside of your foot. A kinematic and kinetic comparison of different intrinsic foot muscle exercises concluded that the short-toe contraction exercise was effective for maintaining that arch under load.³

Their Role in Walking, Running, and Changing Direction

During walking and running, the flexor hallucis longus plays an outsized role. It helps control the big toe as you roll through your stride and provides much of the push-off force at the end of the stance phase. When this tendon is injured, the consequences show up in the pressure map beneath the foot. A study of amateur marathon runners with flexor hallucis longus tendon injuries found that force shifted from the medial (inside) metatarsal regions to the lateral (outside) side of the foot, with decreased contact area under the first metatarsal and increased contact area under the fifth.⁴ That lateral shift can cascade into other problems, altering knee and hip mechanics over thousands of strides.

In high-level athletes, the toe flexors’ contribution to sprinting is especially clear. A study of elite-level competitors found that the torque produced by flexing the metatarsophalangeal joints (the joints at the ball of the foot) was more strongly associated with sprinting performance kinetics at high speed than with other athletic tasks.⁵ That said, the picture is less straightforward for agility. A separate investigation found significant correlations between toe flexor strength and the ability to change direction but no significant correlations between toe flexor strength and straight-line sprint times over 10 or 40 yards.⁶ The takeaway is that strong toe flexors seem to matter most during tasks that demand rapid lateral force production or high-speed ground contact, rather than just running in a straight line at moderate pace.

Falls, Balance, and Aging

If you have an older parent or grandparent, this is the section that matters most. Weak toe flexors are one of the clearest modifiable risk factors for falls in older adults. A prospective study following over 300 older people for twelve months found that those who fell had significantly weaker hallux flexion (about 12 percent of body weight, compared to roughly 15 percent in non-fallers) and weaker lesser-toe flexion. The presence of hallux valgus and lesser-toe deformities further increased fall risk.⁷

A cross-sectional study of community-dwelling older adults added a nuance: toe grip force of the dominant foot specifically was associated with fall history. The non-dominant foot’s grip force was not significantly different between fallers and non-fallers.⁸ This suggests that asymmetry in foot strength testing can hide meaningful deficits when only an average of both feet is reported.

Part of the mechanism behind this fall risk involves sensory feedback, not just muscle force. Microneurography recordings from the intrinsic foot muscles during quiet standing show that muscle spindle endings in these muscles fire in patterns closely correlated with shifts in the center of pressure, primarily along the front-to-back axis. When the body sways, these sensors pick up the change and feed it into the postural control loop.⁹ Weak or atrophied muscles mean fewer, less sensitive sensors, which means slower and less accurate balance corrections.

Connections to Plantar Fasciitis and Hammer Toes

Toe flexor weakness turns up consistently in two of the most common foot complaints. People with plantar fasciitis, the stubborn heel pain that plagues runners and office workers alike, show weaker toe flexors on their affected side compared both to their own unaffected foot and to pain-free controls.¹⁰ A second study confirmed that individuals with plantar heel pain performed worse on plantar flexor tasks and on tests of toe grip strength.¹¹ The relationship is likely bidirectional: weak toe flexors may leave the plantar fascia to absorb more mechanical stress, and pain from the fascia may inhibit toe flexor activation.

Hammer toe deformity tells a different story, one of imbalance rather than pure weakness. In people with hammer toes, the ratio of extensor to flexor muscle strength in toes two through four was roughly two to three times higher than in people without the deformity, and that ratio accounted for about half to nearly two-thirds of the variance in the abnormal joint angle at the metatarsophalangeal joint.¹² In other words, it is not that the extensors are too strong in an absolute sense; it is that the flexors are too weak relative to them, allowing the toe to buckle upward at the base joint.

Diabetic neuropathy offers perhaps the starkest picture of toe flexor atrophy. An MRI study found that in the feet of people with diabetic neuropathy, the cross-sectional area occupied by muscle tissue was just about 8 percent of total foot cross-section at the distal level, compared to roughly 31 percent in non-diabetic controls, representing a 73 percent decrease.¹³ That level of wasting helps explain why diabetic feet are so vulnerable to deformity, ulceration, and further injury.

The Flexor Hallucis Longus in Dance and Surgery

Ballet dancers push the flexor hallucis longus harder than almost anyone else. Going en pointe requires extreme plantarflexion of the ankle and toe, placing enormous demand on this tendon as it wraps behind the ankle and under the foot. Tendinopathy is an occupational hazard. Ultrasound comparisons of dancers clinically diagnosed with FHL tendinopathy, healthy dancers, and non-dancers found that the composite tendon thickness was significantly greater in the tendinopathy group compared to both healthy dancers and non-dancers. Interestingly, there was no significant difference in tendon thickness between healthy dancers and non-dancers, which suggests that the tendon does not simply thicken from heavy use but rather thickens pathologically once injured.¹⁴

The flexor hallucis longus also has an important second life in surgery. When the Achilles tendon suffers a chronic rupture that cannot be directly repaired, surgeons often harvest the FHL tendon and transfer it to take over some of the Achilles’ role. This works because the FHL runs close to the Achilles and can be rerouted without drastically altering foot function. One comparative study found that nine months after surgery, patients who received an FHL transfer were more likely to return to normal activities (about 91 percent versus 73 percent for a different repair method), and by thirty months the functional scores and plantarflexion strength were comparable between groups.¹⁵ A gait analysis study of patients who had undergone FHL transfer for chronic Achilles rupture did not show any marked walking abnormalities afterward, and the FHL muscle belly itself hypertrophied to partially compensate for its new role.¹⁶ The loss of big-toe flexion power after the transfer is generally modest enough that most people adapt without difficulty.

How Toe Flexor Strength Develops Over a Lifetime

Toe flexor strength does not follow the same growth curve as hand grip strength. A cross-sectional study of children, adolescents, and young adults found that hand grip strength increased more or less linearly from childhood through young adulthood, while toe flexor strength rose through childhood and adolescence and then leveled off. The relationship between age and toe flexor strength was non-linear, with body mass also contributing independently.¹⁷ This plateau in the late teens may reflect the fact that once your feet reach adult size and you settle into typical shoe-wearing habits, the stimulus for further strength gains disappears unless you actively train these muscles.

Footwear, Barefoot Training, and Practical Exercises

Modern cushioned shoes may do the toe flexors no favors. A systematic review of barefoot and minimalist-footwear training programs in athletic populations found that most interventions led to significant improvements in intrinsic and extrinsic foot muscle volume, medial arch function, toe flexor strength, and neuromuscular control. The gains were especially clear when programs combined strength, balance, and agility exercises over multiple weeks, though some studies reported increases in muscle volume that did not always translate into proportional strength or performance improvements.¹⁸

Even in children, the effect is measurable. Primary school students who wore minimalist shoes to school daily showed significantly larger cross-sectional areas of the abductor hallucis and flexor digitorum brevis, greater hallux and lesser-toe strength, higher arch height, and longer standing long-jump distances compared to peers in standard shoes.¹⁹ Among adult runners, twelve weeks of transitioning to minimalist shoes increased the muscle volume of the flexor digitorum brevis and the abductor digiti minimi.²⁰

You do not have to ditch your shoes entirely to get benefits. Two targeted exercises dominate the research literature:

Short foot exercise: While standing or sitting, you try to shorten the sole of your foot by drawing the ball of the foot toward the heel without curling the toes. This targets the intrinsic foot muscles that support the arch. A randomized controlled trial in university students with flat feet found that six weeks of the short foot exercise significantly improved toe grip strength and single-leg standing stability, and it also changed the activation timing of hip muscles, suggesting the foot’s influence on whole-leg motor control.²¹
Towel curl exercise: Sitting with a towel on the floor, you use your toes to scrunch the towel toward you. A comparison of the two exercises found that the short foot exercise appeared to train the intrinsic muscles more effectively than the towel curl, although results differed between the dominant and non-dominant legs.²²

The short foot exercise’s superiority likely comes from the way it activates the deeper arch-supporting muscles rather than just the superficial toe curlers. If you can only pick one exercise, the evidence tips toward the short foot.

Why Human Toe Flexors Look Different From Other Primates’

Comparing human feet with those of our closest relatives reveals how thoroughly bipedalism has reshaped these muscles. In chimpanzees, the hallucal (big-toe) muscles are proportionally larger and more powerful, reflecting the chimp’s reliance on the big toe for grasping branches during arboreal locomotion. Orangutans, by contrast, have proportionally larger interosseous and digital extensor muscles, suited to a hook-like grip that does not depend much on the rudimentary big toe.²³ Humans stand out by having the highest mass fraction in the digital flexor muscles among the hominoids studied, consistent with a foot that pushes off during walking rather than grasping during climbing.²⁴

Even the anatomy of a single muscle tells this evolutionary story. A detailed comparison of the flexor digitorum brevis across humans, chimpanzees, and orangutans found that this muscle’s origin sites and nerve supply patterns vary more than previously thought, with dual-origin sites and dual innervation appearing across all three species. In humans, the characteristics of the FDB appear consistent with adaptations to habitual bipedal walking, including a robust, posteriorly elongated heel bone and a shift in the functional axis of the foot toward the medial side.²⁵ The broader evolutionary trajectory of the human foot involved trading most of its grasping ability for features that store and return elastic energy, supporting the demands of long-distance walking and running.²⁶

How Clinicians Measure Toe Flexor Strength

If you visit a physical therapist or sports medicine clinic concerned about your foot function, you may encounter a toe grip dynamometer, a small device you squeeze with your toes while seated or standing. Comparing seated and standing measurements can reveal how well your arch and muscle-tendon complex work together. Ultrasound is increasingly used alongside dynamometry. The cross-sectional area of the abductor hallucis, measured by ultrasound, correlates with big-toe flexion force measured during standing on a pressure platform.²⁷ The physiological cross-sectional area of the flexor digitorum brevis also correlates with multi-toe flexor strength across both sexes.²⁸ These measurements are not yet routine in a standard check-up, but they are becoming more common in fall-prevention clinics and sports medicine settings where foot function is recognized as a trainable variable rather than a fixed trait.