Quadriceps

Four muscles on the front of the thigh that straighten the knee — the muscle you feel working in every squat, stair and stand-up. The rectus femoris also helps flex the hip; the inner VMO helps track the kneecap.

This muscle in 3D

Drag to rotate · scroll to zoom — see the shape, origin and insertion of the quadriceps. 3D model via Sketchfab (CC-BY).

Anatomy

Muscles: Rectus femoris, vastus lateralis, vastus medialis (VMO), vastus intermedius

Origin: Rectus femoris: pelvis (AIIS). Three vasti: shaft of the femur.

Insertion: Patella and, via the patellar tendon, the tibial tuberosity (shin).

Actions:

• Knee extension (all four heads)
• Hip flexion (rectus femoris, the two-joint head)
• Patellar tracking and control (especially VMO)
• Decelerate knee bend on landing (eccentric)

How the muscle works

The four heads converge on the kneecap and pull the shin straight through the patellar tendon. They act as powerful shock absorbers, contracting eccentrically to control the descent of a squat or a landing. Balanced pull (notably the VMO) keeps the kneecap tracking in its groove.

Fibre-type bias: Mixed to fast-twitch — strong and powerful, with postural demand in standing.

Functional role: Standing, squatting, climbing, running, jumping and absorbing landings.

Common problems

• Patellofemoral pain / poor kneecap tracking (often VMO-related)
• Patellar tendinopathy ('jumper's knee')
• Quad strain in sprinting/kicking

Training & stretching

Squats, lunges, step-ups, leg press, leg extensions, Spanish squats (VMO/tendon).

Standing quad stretch (heel to buttock); couch stretch for the rectus femoris.

Fix or train this

• Knee Pain
• Build Muscle (Plateau)