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The Thighs: An Overview

The quadriceps, hamstrings, adductors, and sartorius — the powerhouse muscles between hip and knee.

Before this: The Pelvis & Hips: An Overview

You will be able to

  • Name the four major thigh muscle groups and their primary actions.
  • Explain what a biarticular (two-joint) muscle is, using the hamstrings and rectus femoris as examples.
  • Describe how the quadriceps and hamstrings work as an opposing pair at the knee.
Simplified front view of the right thigh showing the four-part quadriceps femoris covering the front of the femur down to the knee, and the adductor muscle group along the inner thigh.
Thighs — quadriceps femoris and adductors (simplified). A beginner-level schematic of the thigh's front (quadriceps) and inner (adductor) muscle groups.
Illustration: Anatomy Learning Platform (original) · CC0-1.0 (public domain dedication)

⚠ Safety note

Sudden sharp pain, a popping sensation, or inability to bear weight after a thigh injury needs prompt medical evaluation. A trainer coaches squat/lunge/hinge technique; they do not diagnose muscle strains or ligament injuries.

Four groups around one bone

The thigh surrounds the femur with three major groups plus one long specialist muscle:

  • Quadriceps femoris (front) — four heads that straighten the knee.
  • Hamstrings (back) — three muscles that extend the hip and bend the knee.
  • Adductors (inside) — pull the thigh toward the midline and stabilize it side-to-side.
  • Sartorius — the longest muscle in the body, crossing both the hip and knee diagonally.

Two-joint muscles

The hamstrings and the rectus femoris (one of the four quad heads) are biarticular — they cross two joints (hip and knee) instead of one. This means their length and force depend on the position of both joints at once, which is part of why exercise selection (squat vs. Romanian deadlift vs. leg curl) changes which part of a muscle group gets emphasized.

An opposing pair at the knee

At the knee, the quadriceps (extension) and hamstrings (flexion) act as an opposing pair, much like biceps and triceps at the elbow. Balanced strength between them is a common training and injury-prevention goal.

Sources for this lesson

“The quadriceps femoris extends the knee and the hamstrings extend the hip and flex the knee.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

Take the quiz (4 questions)Explore the Thighs

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