Overview

The serratus anterior is a fan-shaped muscle on the side of your ribcage. It wraps beneath the shoulder blade and holds it against the chest wall. It is especially important when you reach, push, or lift your arm overhead.

Location

Begins on the outer surfaces of the upper eight or nine ribs
Wraps around the side of the chest
Attaches along the inner border of the scapula (shoulder blade)

Its saw-tooth slips can be visible along the ribs in lean individuals, which is where the name serratus comes from.

Origin, Insertion, Nerve Supply, and Action

Origin: Outer surfaces of ribs 1–8 or 1–9
Insertion: Front surface of the medial border of the scapula
Nerve supply: Long thoracic nerve, mainly C5–C7
Action: Protracts and upwardly rotates the scapula while holding it against the ribcage

In plain language, it slides your shoulder blade forward when you reach and turns it upward so your arm can continue overhead.

Function

Keeps the scapula flush with the ribcage
Works with the trapezius during overhead elevation
Helps transfer force during pushing and punching
Stabilises the shoulder blade while the arm moves

Structures It Connects To

Scapula — its main attachment
Upper ribs — its broad origin
Trapezius — its partner in upward rotation
Long thoracic nerve — its motor nerve

Movements It Assists

Reaching forward
Push-ups and pressing
Punching
Raising the arm overhead

Common Injuries

Long thoracic nerve injury causing serratus weakness
Scapular winging, where the inner border of the scapula lifts away from the back
Fatigue or poor load tolerance during repeated pressing or overhead activity

Pain Referral Patterns

Serratus-related discomfort may be felt along the side of the ribs or beneath the inner border of the shoulder blade. Those areas can also hurt for many other reasons, so location alone cannot identify the muscle involved.

Clinical Relevance

Clinicians often assess serratus function by watching the scapula during a wall push or arm raise. Visible winging can reflect nerve injury, muscle weakness, pain-related movement changes, or another shoulder problem.

Interesting Facts

It is sometimes called the “boxer’s muscle” because it helps drive the shoulder blade forward during a punch.
The long thoracic nerve runs superficially along the chest wall, making it vulnerable to traction, impact and some surgical procedures.

Long thoracic nerve — supplies the serratus anterior
Scapulothoracic joint — the gliding interface it controls
Trapezius — works with it during overhead movement
Scapula — the bone it stabilises

References

StatPearls. "Anatomy, Thorax, Serratus Anterior Muscles." https://www.ncbi.nlm.nih.gov/books/NBK531457/
Martin RM, Fish DE. Scapular winging: anatomical review, diagnosis, and treatments. https://pmc.ncbi.nlm.nih.gov/articles/PMC2684151/
OpenStax. "Muscles of the Pectoral Girdle and Upper Limbs." https://openstax.org/books/anatomy-and-physiology-2e/pages/11-5-muscles-of-the-pectoral-girdle-and-upper-limbs

Serratus Anterior