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Peroneals

Also called peroneal muscles, fibularis muscles, fibular muscles, peroneus longus, peroneus brevis, peroneus tertius, fibularis longus, fibularis brevis, fibularis tertius, evertors, ankle evertors

The muscles on the outer side of the lower leg that turn the sole of the foot outward. What each one does, how they work in walking and running, what changes after ankle sprains, and how they respond to training.

Region
Lower leg
Starts on (peroneus longus)
the upper two-thirds of the fibula's outer side, the intermuscular septum, and the lateral condyle (outer top) of the shinbone8
Starts on (peroneus brevis)
the lower two-thirds of the fibula's outer surface, and the intermuscular septum8,9,10
Starts on (peroneus tertius)
usually the lower third or half of the fibula, and the intermuscular septum12
Ends on (peroneus longus)
the outer side of the first metatarsal's base, and the medial cuneiform, a wedge-shaped inner midfoot bone (Peroneal tendons)11,44
Ends on (peroneus brevis)
the tuberosity (bump) at the base of the fifth metatarsal, by a tendon running behind the outer ankle bone (Peroneal tendons)9,44
Ends on (peroneus tertius)
most often the fifth metatarsal, at its base, shaft or both; in about a third, the fourth and fifth metatarsals12
Tendons
Peroneal tendons
Muscles
peroneus longus, peroneus brevis, peroneus tertius
Updated
October 5, 2026
Reviewed
October 5, 2026 · how entries are checked

Function

Which muscles make up the group

The leg has four compartments, and the lateral one holds the peroneus longus and the peroneus brevis1. Anatomical naming has replaced “peroneal” with “fibular”, so the peroneus longus is also called the fibularis longus1,2. A third muscle, the peroneus tertius, lies in the anterior compartment instead, at the front of the lower leg7,8.

The left panel shows the superficial muscles that move the feet and the center panel shows the posterior view of the same muscles. The right panel shows the deep muscles of the right lower leg.
Muscles of the lower legBetts JG, Young KA, Wise JA, et al. Anatomy and Physiology, Figure 11.32. OpenStax, 2013. Access for free at openstax.org. (source, CC BY 4.0). Resized to 1600 pixels wide.

The peroneus longus arises from the upper two-thirds of the outer side of the fibula, the thin outer bone of the lower leg8. Part of it arises from the outer top of the tibia (shinbone)8. The peroneus brevis arises from the lower two-thirds of the fibula’s outer surface9,10. Both also take fibres from an intermuscular septum, a sheet of tough tissue that separates groups of muscles8,9.

Both tendons pass behind the lateral malleolus, the bony bump on the outer side of the ankle9,11. The longus tendon then wraps beneath the foot to reach its inner side11. The brevis tendon attaches at the base of the fifth metatarsal, the long foot bone behind the little toe9. The peroneal tendons have their own page.

The peroneus tertius

The peroneus tertius usually arises from the lower third or half of the fibula and from the intermuscular septum12. A systematic search of anatomical studies found it most often ends on the base of the fifth metatarsal12. Not everyone has one. A meta-analysis (a study that pools earlier results) of 25 studies of cadavers (bodies donated for study) gave a weighted prevalence of 93.2%12.

Their nerves and blood supply

The superficial fibular nerve supplies the peroneus longus and brevis8,9,10. The deep fibular nerve supplies the peroneus tertius7. The lateral compartment gets its blood from the anterior tibial and fibular arteries1,2.

What they move

The main action of the longus and brevis is eversion of the foot and ankle1. Plantar flexion (pointing the foot down) and support of the foot’s arches are secondary1. The brevis is credited with roughly 60% to 65% of the eversion force at the ankle8,9. The peroneus tertius everts the foot and dorsiflexes it, pulling it up toward the shin13. It has been described as levelling the sole while the foot swings forward, before the next touchdown12.

Whether the longus holds up the arch

One anatomical source describes the peroneus longus as stabilising the long inner arch of the foot11. Three cadaver studies tested this by pulling on its tendon, and they do not agree14,15,16:

  • In seven specimens, a stronger pull rotated the inner column of the foot toward eversion, which the authors read as stabilising that column14.
  • In eight feet, the pull reduced bone movement but lowered the foot’s stiffness and raised the energy it stored15.
  • In eight pairs of legs, a 15 kg pull rotated the first metatarsal but did not significantly change the arch angle16.

The authors of the third study said their result calls into question how much the tendon maintains the arch16.

What they do in walking and running

In walking, the peroneals are most active in mid-stance, when one leg alone supports the body3. Stance is the part of each step when the foot is on the ground. They are also active at push-off3. One study measured 16 healthy people walking on the flat and across a sideways slope3. Average peroneus longus activity during stance, as a share of the muscle’s hardest effort with the joint still, was3:

Peroneus longus activity (% of hardest effort)Flat ground14 Side slope, foot flat on it58 Side slope, outer edge of the foot raised77
Peroneus longus activity (% of hardest effort). Bars start at zero; the table below gives each value with its source.
Walking surfacePeroneus longus activity (% of hardest effort)
Flat ground143
Side slope, foot flat on it583
Side slope, outer edge of the foot raised773

These figures are approximate3. In the same people, peroneus brevis activity was about 15% on the flat and about 45% to 53% across the slope3.

In 15 injury-free recreational and competitive runners tested at three paces, peroneus brevis activity rose significantly as pace increased17. Ten men ran in shoes wedged to tilt the foot inward, outward or neither way18. The activation patterns of the muscles recorded, the peroneus longus among them, did not change with the shoe18.

How fast they can react

The longus and brevis are described as integral to controlling supination (the foot rolling outward onto its outer edge) and guarding against lateral ankle sprains19. One study found a protective reflex from the peroneals would take at least 126 milliseconds after a sudden, unexpected inversion19. That figure assumes the muscles are not already active before the heel touches down19. The peroneals are in fact active before touchdown when going down stairs and landing from a jump19.

A walking study of 25 people with chronic ankle instability and 10 controls reached a more cautious view20. Its authors concluded that the peroneus longus serves balance and cannot be relied on to stop an inversion injury in normal walking20.

Breakdown

What studies find after ankle sprains

Chronic ankle instability is an ankle that stays loose or keeps giving way after one or more sprains. The ankle sprain page covers the condition itself. Reviews have compared people who have it with controls21,22:

What was measuredWhat the review found
Reaction to sudden inversionDelayed after an earlier sprain, most with chronic instability, in a review of 23 studies4
Peroneus longus timingLate activation in sudden inversion and in landing on unstable surfaces, reported by a review of 63 muscle-activity studies23
Activity just before landingLess peroneus longus activity before a single-leg jump landing, in a review of 21 studies24
Eversion strength, 20 studiesLower than controls in shortening and lengthening work, with standardised mean differences of 0.73 to 0.9521
Eversion strength, search to 2007Ankles with functional instability were weaker in shortening work, by a small difference of 0.22425
Sense of eversion forceLess accurate at 10% and 20% of hardest effort; each result rested on two small studies26
Spinal reflex in the longusLower excitability, with a small effect, across 17 studies22

A standardised mean difference puts the gap between two groups on a common scale. A review of reviews found strong evidence that deficits in peroneal reaction time, eversion strength and balance contribute to ankle instability27. Only 17% of its primary studies measured a clearly defined chronic ankle instability group27.

Size and activity in unstable ankles

A study using ultrasound, a scan made with sound waves, compared 29 people with chronic ankle instability and 29 healthy controls, aged 18 to 3028. The instability group had a smaller peroneal cross-sectional area (the size of a slice cut straight across a muscle) when standing28. The groups did not differ when lying on the side28.

In treadmill walking, 15 adults with chronic ankle instability had the peroneus longus active for 36.0% of the stride29. In 15 matched healthy controls the figure was 23.3%29.

Tears and pressure in the lateral compartment

A case report describes a 23-year-old collegiate football player with a large tear in the upper peroneus longus muscle belly30. The player felt a sharp leg pain in practice, with no contact, and developed acute lateral compartment syndrome30. Compartment syndrome is a rise in pressure inside a closed space of muscle, which limits blood flow there. Rupture of this muscle after a twisting ankle injury is a known, though uncommon, cause of it30.

One institution saw 26 people over 11 years with chronic exertional compartment syndrome confined to the lateral compartment31. Their median (middle) age was 2131. Running and walking were among the activities they most often named as provoking it31. In another series of 73 people with exertional leg pain and raised compartment pressures, 5 (7%) had raised pressure in the lateral compartment alone32.

Recovery

How they respond to training in healthy people

Twenty healthy people were randomly split to train either the longus or the brevis with elastic bands for 8 weeks33. The cross-sectional area and ankle strength of the trained muscle rose significantly33. Some of the size gain was still present in the period after training stopped33.

Trials of reaction time and strength have mixed results34,35:

  • In 24 healthy male recreational athletes, 6 weeks of isokinetic training shortened the peroneus longus reaction to a sudden foot tilt34.
  • In 26 healthy, active college-age people, 6 weeks of neuromuscular training shortened peroneus longus reaction time during walking, compared with controls36.
  • In a randomised trial of 40 people, 4 weeks of elastic-resistance training changed neither eversion strength nor peroneus longus reaction time35.

Isokinetic training uses a machine that holds a limb to a fixed speed. Neuromuscular training is exercise aimed at how nerves and muscles work together. Half of the 40 people in the third trial had a history of ankle sprains35.

How they respond in people with unstable ankles

In a randomised trial of 39 people with chronic ankle instability, 6 weeks of strength training improved eversion strength37. The untrained control group did not improve37.

Two studies of muscle size after a 4-week supervised exercise programme point different ways5,6. In 26 people with chronic ankle instability, peroneal cross-sectional area on ultrasound rose from 3.44 to 3.72 cm²5. The untrained leg showed a similar rise5. In a preliminary study of five young adults using MRI, a detailed scan, the programme did not enlarge the peroneals6. Eversion strength in those five still improved by a large amount6.

Connections

Tendons, bones and nerves

The peroneus brevis becomes tendon 2 to 3 cm above the tip of the fibula8. From there down, the peroneal tendons page takes over. The longus tendon attaches to the base of the first metatarsal and to the medial cuneiform, a wedge-shaped bone of the inner midfoot11. Both muscles start on the fibula, and the longus also on the tibia8,9,10.

At the neck of the fibula, the common fibular nerve divides into the superficial and deep fibular nerves38. The superficial one is the motor supply of the peroneus longus and brevis39.

Muscles and joints they work with

At the ankle, the longus and brevis point the foot down and turn the sole outward40. The everting pull of the peroneus tertius is described as countering the inverting pull of the tibialis anterior12. In 10 active men doing side-shuffle and cutting moves, the tibialis anterior and peroneus longus steadied the subtalar joint41. The subtalar joint sits between the talus and the heel bone, just below the ankle joint.

Exercises that load them

Related exercise pages: running, calf raise, drop landing, single-leg Romanian deadlift17,19,42,43.

ExerciseWhat studies found
Calf raiseIn 14 healthy men, peroneus longus activity was highest with the foot turned out 30°42
Single-leg Romanian deadliftIn 28 healthy athletes holding a sandbag, it gave more peroneus longus activity than standing still on one leg43
Drop landingThe peroneals are active before the foot touches down when landing from a jump19

Peroneals pulls through

Peroneals starts on

Peroneals starts partly on

Peroneals attaches to

Peroneals is supplied by branches of

Peroneals moves

Peroneals works alongside

Peroneals changes after

Peroneals is loaded by

Sources

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Every source the library cites

Changes

  • First published.