Dominic Stone
The human foot is a complex structure, with over 20 muscles that help enable movement and give the foot its shape. These muscles can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are found in the lower leg and act to dorsiflex, plantarflex, invert and evert the foot. The intrinsic muscles, on the other hand, are entirely contained within the foot and primarily act to move the toes and stabilise the foot. The foot and ankle's complex joint structure allows it to handle tremendous stress and compensate for a wide variety of unpredictable forces.
| Characteristics | Values |
|---|---|
| Number of muscles in the human foot | 29 |
| Number of extrinsic muscles | 10 |
| Number of intrinsic muscles | 19 |
| Number of compartments in the foot | 9 |
| Number of layers of plantar muscles | 4 |
| Number of lumbrical muscles | 4 |
| Number of muscles in the dorsal group | 2 |
| Number of plantar groups | 3 (lateral, central, and medial) |
| Innervation source for extrinsic muscles | Deep fibular nerve |
| Innervation source for intrinsic muscles | Medial or lateral plantar nerves |
| Function of extrinsic muscles | Actions such as eversion, inversion, plantarflexion, and dorsiflexion |
| Function of intrinsic muscles | Fine motor actions, e.g., movement of individual digits, flexion, extension, and abduction |
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What You'll Learn
Foot muscles help with movement and balance
The human foot is a complex structure, with 20 or more muscles that help enable movement and give the foot its shape. The foot and ankle are the only parts of the body that come into contact with the ground during single-leg standing, so the foot must be stable enough to maintain the body's centre of mass. The foot's muscles contribute to the stability of the foot itself and the whole body.
The muscles of the foot can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are found in the lower leg and act to dorsiflex, plantarflex, invert and evert the foot. The intrinsic muscles, on the other hand, are entirely contained within the foot and primarily act to move the toes. These muscles are also responsible for stabilising the foot and supporting the arches to maintain foot structure. They also aid the actions of the muscles of the lower leg to produce fine movements of the toes.
The intrinsic foot muscles are a group of muscles that reside within the foot. Both anatomical attachments (origin and insertion) of these muscles are in the foot. This is a key distinguishing feature from the extrinsic muscles that have their origin in the leg and long tendons that course the ankle to insert at the foot. The intrinsic foot muscles are primarily located on the plantar aspect of the foot, with a few exceptions. The size of the intrinsic foot muscles varies considerably, from the abductor hallucis, which is typically the largest, to the lumbricals, which are typically the smallest.
The plantar intrinsic foot muscles are essential functional structures during bipedal running and walking. They enhance our ability to produce forward propulsion from one stride to the next, which confirms their role in human locomotion. The foot has two longitudinal arches: lateral and medial. The plantar intrinsic foot muscles play an important role in supporting these arches. In running and walking, most of the intrinsic muscles are immediately activated as the foot touches the ground.
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Intrinsic and extrinsic muscles
The muscles of the foot can be divided into two main groups: extrinsic and intrinsic muscles. The foot has 29 muscles associated with it, 10 of which are extrinsic muscles, and 19 are intrinsic muscles.
Extrinsic Muscles
Extrinsic muscles originate in the lower leg and extend into the foot. They are responsible for gross motor movements such as plantar flexion, dorsiflexion, inversion, and eversion. The extrinsic muscles are further divided into anterior, lateral, and posterior compartments, each housing specific extrinsic muscles. The anterior compartment contains the extensor digitorum longus, extensor hallucis longus, and peroneus tertius muscles. The lateral compartment hosts the peroneus longus and peroneus brevis muscles, aiding in eversion and plantar flexion of the foot, and providing stability during walking and running. The posterior compartment is home to the gastrocnemius, soleus, and plantaris muscles.
Intrinsic Muscles
Intrinsic muscles, on the other hand, are located entirely within the foot and are responsible for fine motor movements, such as digit flexion, extension, and abduction. They can be further divided into two groups: the dorsal group and the plantar group. The dorsal group consists of two muscles: the extensor digitorum brevis and extensor hallucis brevis, which are responsible for extending the toes. The plantar group consists of four layers of muscles, going from superficial to deep within the foot. The first layer contains muscles that lie immediately deep to the plantar aponeurosis in the sole of the foot, including the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi. The second layer contains the quadratus plantae and the lumbricals.
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Foot arches and toes alignment
The foot is made up of many muscles, ligaments, tendons, and bones. The muscles in the foot can be divided into two main categories: extrinsic and intrinsic muscles. The foot's extrinsic muscles originate in the lower leg, while the intrinsic muscles are located within the foot. The extrinsic muscles are responsible for actions such as eversion, inversion, plantar flexion, and dorsiflexion of the foot. On the other hand, the intrinsic muscles are responsible for fine motor actions, such as the movement of individual digits.
The proper function of the muscular systems that shape the arches of the foot is crucial for the correct alignment of the big toe (hallux) and other toes. The muscles work together to stabilize the foot arches and individually control the movement of the toes. The abductor hallucis muscle, for example, contributes to a small soft tissue bulge on the medial side of the sole and is responsible for the abduction and flexion of the great toe. The flexor digitorum brevis muscle, located next to the abductor hallucis, also plays a role in toe alignment.
Additionally, muscle systems I–III provide a physiological course for the foot muscles, which have distal inserts located on the phalanges of the big toe and are directly responsible for its alignment. System IV, in cooperation with System III, stabilizes the medial longitudinal arch and influences the alignment of the toes, including the hallux. System V, or the "reins of hallux", consists of muscles that are directly responsible for the proper alignment of the hallux, including the flexor hallucis longus and brevis, extensor hallucis brevis, adductor, and abductor hallucis.
The analysis of static deformities, such as hallux valgus, requires considering the extrinsic muscles of the foot. Correct arches of the foot ensure the proper pulling force of both the extrinsic and intrinsic muscles, which then determines the physiological alignment of the toes. A balanced isometric contraction of the external muscles ensures proper foot architecture and the alignment of the tendons attached to the phalanges of the toes.
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Ankle-foot unit
The foot and ankle form a complex system consisting of 28 bones, 33 joints, 112 ligaments, and 34 muscles. The foot and ankle are crucial for supporting body weight, providing balance, absorbing shock, and enabling movement. The foot can be divided into three main compartments: anterior, lateral, and posterior, each housing specific extrinsic muscles. The ankle is the joint that connects the foot to the lower leg.
The ankle is a synovial joint, which means it has the most freedom to move. It is functionally a hinge joint, allowing for dorsiflexion and plantarflexion movements in the sagittal plane. The ankle is also referred to as the tibiotalar joint or the talocrural joint. The ankle joint is where the shin bone (tibia), calf bone (fibula), and talus bone meet. The subtalar joint allows for inversion and eversion of the ankle and hindfoot.
The foot muscles can be broadly categorized into extrinsic and intrinsic muscles. The extrinsic muscles originate in the lower leg and are responsible for gross motor movements such as plantar flexion, dorsiflexion, inversion, and eversion. The intrinsic muscles, located within the foot, control fine movements and maintain the foot's arches. These include muscles such as the abductor hallucis, flexor digitorum brevis, and plantar interossei.
The extrinsic muscles of the foot play a crucial role in foot function, providing stability, enabling movement, and supporting the body. The intrinsic muscles of the foot are further divided into dorsal and plantar groups, with four layers of plantar muscles. The plantar muscles work together to stabilize the foot's arch and control the movement of the toes.
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Muscle systems
The human foot contains over 20 muscles that enable movement and give the foot its shape. The muscles of the foot can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are found in the lower leg and enable the dorsiflexion, plantar flexion, inversion, and eversion of the foot. The intrinsic muscles, on the other hand, are entirely contained within the foot and primarily act to move the toes. These muscles are smaller but play a mighty role in foot and ankle function, stabilising the foot and supporting the arches.
The intrinsic foot muscles are further categorised into dorsal and plantar muscles. The dorsal group consists of the extensor digitorum brevis and extensor hallucis brevis, which act to extend the toes. The plantar intrinsic foot muscles are essential during bipedal running and walking, enhancing our ability to produce forward propulsion. They also play a crucial role in supporting the foot's longitudinal arches. The size of the intrinsic muscles varies, with the abductor hallucis typically being the largest, and the lumbricals usually the smallest.
The extrinsic muscles of the foot include the tibialis anterior, which causes inversion, and the fibularis tertius, which causes eversion. The lateral compartment contains the fibularis longus and brevis, which plantar flex and evert the foot. The posterior compartment muscles are divided into the superficial and deep layers. The gastrocnemius, one of the large muscles of the leg, connects to the heel and flexes the foot, ankle, and knee. The soleus muscle, extending from the back of the knee to the heel, is pivotal in walking and standing.
The intrinsic muscles of the foot have multiple segments, allowing the central nervous system to generate a range of force vectors. This enables fine-tuning of movements through targeted contractions of specific muscle segments. These muscles also stiffen the foot and support the arches, generating propulsion during walking and running. Without their active contraction, the stiffening of the forefoot during push-off against the ground would be challenging, impairing the ability to generate propulsive power.
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Frequently asked questions
The foot muscles can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are found in the lower leg and help the foot to dorsiflex, plantarflex, invert and evert. The intrinsic muscles are entirely contained within the foot and primarily move the toes. There are 20+ muscles in the foot, including tendons, that help enable movement and give the foot its shape.
The extrinsic foot muscles include the tibialis anterior, extensor hallucis longus, and extensor digitorum longus. The lateral compartment houses the fibularis longus and fibularis brevis, which plantar flex and evert the foot.
The intrinsic foot muscles include the dorsal and plantar muscles of the foot. The dorsal group consists of the extensor digitorum brevis and extensor hallucis brevis, which extend the toes. The plantar intrinsic foot muscles include the abductor hallucis, which is the largest, and the lumbricals, which are the smallest.
