Muscles of the Lower Limb: Structure, Function, and Compartmentalization

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Muscles of the Body

Overview of Lower Limb Musculature

The muscles of the lower limb are organized into compartments based on their location and function. These muscles are essential for movement, stability, and support of the body during locomotion. The main compartments include the anterior, medial, lateral, and posterior regions of the thigh and leg, as well as intrinsic muscles of the foot.

Muscles of the Thigh

Anterior and Medial Muscles of the Thigh

The anterior and medial compartments of the thigh contain muscles responsible for flexion, extension, and adduction of the hip and knee. The quadriceps femoris is the primary extensor of the knee, while the adductor group is responsible for thigh adduction.

Quadriceps femoris: Composed of four heads (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius), all inserting at the quadriceps tendon and patella. Powerful knee extensors.
Sartorius: Flexes, abducts, and laterally rotates the thigh; also flexes the knee.
Iliopsoas: Major hip flexor, formed by the iliacus and psoas major muscles.
Adductor group: Includes adductor longus, adductor brevis, adductor magnus, pectineus, and gracilis; responsible for adduction of the thigh.

Superficial muscles of anterior and medial thigh

Posterior Gluteal Muscles and Lateral Rotators

The posterior compartment and gluteal region contain muscles that extend, abduct, and laterally rotate the thigh. The gluteal muscles are crucial for hip stability and movement.

Gluteus maximus: Main extensor of the hip.
Gluteus medius and minimus: Abduct and medially rotate the thigh.
Lateral rotators: Include piriformis, obturator externus/internus, superior/inferior gemellus, and quadratus femoris; responsible for lateral rotation of the thigh.

Lateral rotators of the thigh, deep muscles of gluteal region Posterior muscle of the hip and thigh, superficial view and cadaver dissection

Muscles of the Posterior Compartment of the Thigh

The posterior compartment contains the hamstring muscles, which are responsible for extension of the hip and flexion of the knee.

Biceps femoris
Semitendinosus
Semimembranosus

Muscles of the Leg

Anterior Compartment

The anterior compartment muscles dorsiflex the foot and extend the toes. They are important for walking and running.

Tibialis anterior: Dorsiflexes and inverts the foot.
Extensor digitorum longus: Extends toes and dorsiflexes foot.
Extensor hallucis longus: Extends big toe and dorsiflexes foot.
Fibularis tertius: Dorsiflexes and everts the foot.

Anterior muscles of the leg, superficial view and cadaver dissection Muscles of the anterior leg shown in isolation

Lateral Compartment

The lateral compartment muscles evert the foot and assist in plantar flexion.

Fibularis longus
Fibularis brevis

Lateral aspect of the leg, superficial view and cadaver dissection Muscles of the lateral leg shown in isolation

Posterior Compartment

The posterior compartment muscles are divided into superficial and deep groups. They are responsible for plantar flexion and toe flexion.

Superficial muscles: Triceps surae (gastrocnemius, soleus), plantaris.
Deep muscles: Popliteus, flexor digitorum longus, flexor hallucis longus, tibialis posterior.

Posterior compartment of the leg, superficial view and gastrocnemius removed Muscles of the posterior compartment of the right leg Deep muscles of the posterior leg shown in isolation

Intrinsic Muscles of the Foot

Overview and Function

The intrinsic muscles of the foot are responsible for toe movement and maintaining the arches of the foot. They are divided into layers on the dorsal and plantar aspects.

Dorsal aspect: Extensor digitorum brevis.
Plantar aspect: Multiple layers including flexor digitorum brevis, abductor hallucis, abductor digiti minimi, flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis, and interossei muscles.

Muscles on the sole of the foot, first layer Third layer muscles of the foot Fourth layer: plantar and dorsal interossei

Muscle Layers of the Foot

First layer: Flexor digitorum brevis, abductor hallucis, abductor digiti minimi.
Third layer: Flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis.
Fourth layer: Plantar and dorsal interossei.

Summary Table: Major Muscles of the Lower Limb

Compartment	Muscles	Main Actions
Anterior Thigh	Quadriceps femoris, Sartorius, Iliopsoas	Knee extension, hip flexion
Medial Thigh	Adductor longus, brevis, magnus, Pectineus, Gracilis	Thigh adduction
Posterior Thigh	Biceps femoris, Semitendinosus, Semimembranosus	Hip extension, knee flexion
Gluteal Region	Gluteus maximus, medius, minimus, Lateral rotators	Hip extension, abduction, lateral rotation
Anterior Leg	Tibialis anterior, Extensor digitorum longus, Extensor hallucis longus, Fibularis tertius	Dorsiflexion, toe extension
Lateral Leg	Fibularis longus, Fibularis brevis	Eversion, plantar flexion
Posterior Leg	Gastrocnemius, Soleus, Plantaris, Popliteus, Flexor digitorum longus, Flexor hallucis longus, Tibialis posterior	Plantar flexion, toe flexion
Foot (Intrinsic)	Extensor digitorum brevis, Flexor digitorum brevis, Abductor hallucis, Abductor digiti minimi, Flexor hallucis brevis, Adductor hallucis, Flexor digiti minimi brevis, Interossei	Toe movement, arch support

Example: The quadriceps femoris is essential for activities such as walking, running, and jumping, as it extends the knee and stabilizes the leg.

Additional info: The compartmentalization of muscles allows for coordinated movement and efficient force generation during complex activities such as gait and balance.