Muscles of the Lower Limb

Topic 2.4: Muscles of the Lower Limb

Learning Outcomes

  • Identify and describe the actions of selected muscles that:

    • Move the thigh at the hip joint.

    • Move the lower leg at the knee.

    • Move the foot and toes.

Hip Joint Muscles

  • Muscles Acting at Hip Joint (Flexion):- Iliopsoas (Iliacus & Psoas Major):

    • Comprises two major muscles that act together as the prime mover for hip flexion, crucial for movements such as walking and climbing stairs.

    • The iliacus originates from the iliac fossa of the pelvis and joins the psoas major, which originates from the lumbar vertebrae, to insert on the lesser trochanter of the femur.

    • Anterior Thigh Muscles:

    • Rectus Femoris:

      • A part of the quadriceps group, it plays a dual role in hip flexion as it crosses the hip joint while also extending the knee; originates from the anterior inferior iliac spine (AIIS) and inserts via the patellar tendon to tibial tuberosity.

    • Sartorius:

      • The longest muscle in the body, it originates from the ASIS (anterior superior iliac spine) and performs multiple actions: it flexes, abducts, and laterally rotates the hip; it also assists in knee flexion, earning the nickname "Tailor's muscle" for its role in sitting cross-legged.

    • Tensor Fascia Latae:

      • This muscle assists in flexing, abducting, and medially rotating the thigh and plays a key role in stabilizing the pelvis when walking or running by tensing the iliotibial tract.

Posterior Hip Muscles (Extension)

  • Gluteus Maximus:

    • The largest muscle in the gluteal region, it is the primary extensor of the hip, crucial for actions like standing up from a sitting position and running; it also laterally rotates the thigh and assists in stabilization of the hip and pelvis.

  • Gluteus Medius:

    • Located beneath the gluteus maximus, it is vital for pelvic stability during ambulation, abducts the thigh, and plays a role in medially rotating the thigh to assist in movements such as walking and running.

  • Gluteus Minimus:

    • Works similarly to the gluteus medius, providing abduction and medial rotation of the hip, and also stabilizes the pelvis while moving.

  • Hamstring Muscles:

    • This group includes Biceps Femoris, Semitendinosus, and Semimembranosus; primarily responsible for hip extension and knee flexion during activities such as running and jumping, all originate from the ischial tuberosity and insert onto the tibia and fibula, innervated by the tibial division of the sciatic nerve.

Medial Hip Muscles (Adduction)

  • Adductor Group:

    • Comprising Adductor Longus, Brevis, and Magnus, these muscles contribute to the adduction, flexion, and medial rotation of the hip, playing a significant role in stabilizing the pelvis during walking and maintaining balance.

  • Gracilis:

    • A slender muscle that also adducts, flexes, and medially rotates the hip, it is important for movements requiring the stabilization of the lower body, such as squatting.

  • Innervation:

    • The entire adductor group is innervated by the obturator nerve, highlighting the coordinated nature of these muscles during lower limb movements.

Knee Joint Muscles

  • Anterior Compartment (Knee Extension):

    • Quadriceps Femoris Group:

      • Comprises four muscles: Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Vastus Intermedius; these are the primary knee extensors, inserting into the patellar ligament, with the rectus femoris additionally flexing the hip joint; critical for activities like standing up, walking, and running.

  • Posterior Compartment (Knee Flexion):

    • Hamstrings:

      • They are the prime movers for knee flexion; each muscle originates ideally from the ischial tuberosity, with different insertions providing effective leverage for flexing the knee in various activities. They are innervated by the tibial portion of the sciatic nerve.

Ankle and Foot Muscles

  • Superficial Muscles in Posterior Lower Leg (Plantarflexion):

    • Gastrocnemius:

      • Acts to plantarflex the ankle when the knee is extended and also flexes the knee joint, making it a dual function muscle necessary for activities such as jumping.

    • Soleus:

      • Lies deep to the gastrocnemius, crucial for postural stability when standing and walking; active in plantarflexion throughout daily activities.

    • Plantaris:

      • A small muscle that assists in knee flexion and plantarflexion of the ankle, often considered vestigial in nature.

    • All muscles in this group are innervated by the Tibial nerve.

  • Anterior Compartment Muscles:

    • Tibialis Anterior:

      • The primary mover of dorsiflexion, this muscle also inverts the foot and supports the medial longitudinal arch, playing a crucial role in proper gait.

    • Extensor Hallucis Longus:

      • Dorsiflexes the ankle and extends the big toe, contributing to proper foot clearance during walking.

    • Extensor Digitorum Longus:

      • Dorsiflexes ankle and extends the lateral four toes, important for walking and running mechanics.

  • Deep Muscles in Posterior Lower Leg:

    • Flexor Halluces Longus:

      • Functions to plantarflex the ankle, invert the foot, and flex the big toe, essential for balance and propulsion during the push-off phase of walking.

    • Flexor Digitorum Longus:

      • Similar in function to the flexor halluces but targets the other four toes, facilitating gripping movements with the toes for stabilization.

    • Tibialis Posterior:

      • The prime mover of foot inversion, it also helps stabilize the medial arch of the foot during walking and weight-bearing activities.

    • Popliteus:

      • Unlocks the knee joint from full extension, allowing for flexion upon initiation of walking or running.

  • Lateral Compartment Muscles:

    • Fibularis Longus:

      • Everts the foot and assists in some plantarflexion, playing a role in the lateral stability of the ankle.

    • Fibularis Brevis:

      • Also contributes to foot eversion and assists in plantarflexion, further supporting lateral stability.

Compartment Summary

  • Anterior Compartment: Primarily involved in dorsiflexion of the ankle and extension of the toes, essential for maintaining a proper walking gait.

  • Posterior Compartment: Major actions include plantarflexing the ankle, inverting the foot, and flexing the toes, crucial for various movements such as running and jumping.