Leg muscles: structure and function

The muscles of the lower limb move the hip, knee and ankle joints. Among them, the anterior and posterior thigh muscles are especially important: they are involved in walking, running, jumping and strength movements.

Quadriceps femoris

The quadriceps is made up of four parts

• Rectus femoris
• Vastus lateralis
• Vastus medialis
• Vastus intermedius

All four muscles merge into a common tendon that attaches to the kneecap (patella) and then continues as the patellar ligament, which inserts on the tibia.

Main function

The main function of the quadriceps is extension of the lower leg at the knee joint.

Rectus femoris

The rectus femoris is the longest part of the quadriceps and the only two-joint muscle in the group.

Anatomy

It originates from the anterior inferior iliac spine and joins the common quadriceps tendon.

Functions

• Hip flexion
• Knee extension

Because this muscle acts on two joints, its activity depends on body position and the position of the pelvis.

Vastus lateralis, medialis and intermedius

These three muscles lie on the femur and take part in only one movement.

Function

• Knee extension

The vastus intermedius lies deep and is covered by the rectus femoris.

Quadriceps activation in exercises

The quadriceps works hard in both isolation and multi-joint exercises.

Multi-joint exercises

For example:

• Squats
• Leg press
• Bulgarian split squats

In these movements the vastus lateralis, medialis and intermedius are activated the most, while rectus femoris activity is relatively lower, because it is also involved in hip flexion.

Isolation exercises

The rectus femoris works harder in movements that involve knee extension with the hip in a relatively extended position,

For example

• Leg extensions on a machine
• Sissy squats
• Cable front leg raises

Muscles of the back of the thigh (Hamstrings)

The posterior thigh group consists of three main muscles:

• Semitendinosus
• Semimembranosus
• Biceps femoris

Semitendinosus and semimembranosus

These muscles are located on the medial side of the thigh.

Functions

• Hip extension
• Knee flexion
• Internal rotation of the lower leg with the knee bent

Biceps femoris

This muscle is located on the lateral side of the thigh and has two heads:

• Long head
• Short head

Functions of the long head

• Hip extension
• Knee flexion
• External rotation of the lower leg

Function of the short head

• Knee flexion

Hamstring activation in exercises

• Barbell deadlift
• Romanian deadlift
• Leg curls on a machine
• Glute bridges

Knee flexion loads the distal part of the muscles more, while hip extension places more load on the proximal part.

Author: Irakli Kenchoshvili / Tidanigym.ge

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