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Barbell Back Squat

Also called: Back squat

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)

Primary muscles: Quadriceps femoris

Secondary muscles: Gluteus maximus, Hamstrings, Adductors (hip adductor group)

Joints / actions: Knee joint (tibiofemoral joint) (extension); Hip joint (coxal joint) (extension)

Plane: sagittal

Equipment: barbell

What it is

With a barbell across the upper back, bending the hips and knees to lower the body and then standing back up.

Purpose

A foundational full-lower-body exercise that builds the quadriceps, glutes, and hamstrings together.

Starting position

Stand with the barbell resting across the upper back (not the neck), feet roughly shoulder-width, toes slightly turned out.

Step by step

Brace the core, then bend the hips and knees together to lower the body, keeping the chest up and the heels down.
Lower to a depth you can control with a neutral spine — for most beginners, thighs roughly parallel to the floor.
Drive through the whole foot to stand back up, keeping the knees tracking in line with the toes.

Breathing

Inhale and brace before descending; exhale as you drive up to standing.

Coaching cues

"Chest up, sit down and back, knees track over your toes, drive the floor away."

Common mistakes

Letting the knees cave inward; rounding the low back at the bottom; rising onto the toes; descending faster than can be controlled.

Easier regression

Bodyweight squat, box squat (sitting to a box to control depth), or goblet squat with a lighter, front-loaded weight.

Harder progression

Add load gradually, or increase depth/tempo control once technique is consistent.

Alternatives

Goblet squat, leg press, front squat.

Who may benefit

Almost everyone building lower-body strength; foundational for sport, general fitness, and daily function (sitting/standing).

Who should modify or avoid it

Those with knee or hip pain that worsens with depth should regress depth or load and seek individualized coaching.

Why this exercise works

By moving through a large range at both the hip and knee simultaneously, the squat loads the quadriceps (knee extension), glutes and hamstrings (hip extension), and adductors (frontal-plane stability) together — one of the most complete lower-body exercises available.

⚠ Safety note

Squat only as deep as a neutral spine and controlled knee position can be maintained; use a spotter or safety pins when adding significant load.

Sources

“The quadriceps femoris extends the knee and the gluteus maximus/hamstrings extend the hip, the two joint actions combined in a squat.”

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