Push-up muscles worked

Every role here is for this technique: hands a little wider than the shoulders, body held in a straight line from head to heels, chest lowered to just above the floor.

What muscles does the push-up work?

The prime movers of the push-up are both parts of pectoralis major, the anterior deltoid and triceps brachii. They produce shoulder horizontal adduction and elbow extension. The synergists are serratus anterior and coracobrachialis. Eleven stabilizers hold joints and segments still, among them rectus abdominis, external oblique and internal oblique. The roles follow NSCA (2016) and Neumann (2017).

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Joint actions and their prime movers

The joint actions of the push-up and the prime movers that produce each
Joint action	Prime movers
Shoulder horizontal adduction	Both parts of pectoralis major and the anterior deltoid
Elbow extension	Triceps brachii

Every muscle by role

A prime mover produces the lift’s main joint action against the load; a synergist assists that action, or adds a secondary action the lift needs; a stabilizer contracts mostly isometrically to hold a joint or a segment still. A role describes what the muscle does in the technique above, not how hard it works or how much it grows.

Prime movers 4

Prime movers in the push-up, with what each does
Muscle	What it does here
Pectoralis major, sternal part	Pushing the chest away from the hands
Pectoralis major, clavicular part	Pushing the chest away from the hands
Anterior deltoid	Shoulder flexion and horizontal adduction
Triceps brachii	Elbow extension, all three heads

Synergists 2

Synergists in the push-up, with what each does
Muscle	What it does here
Serratus anterior	Pushing the shoulder blades forward at the top
Coracobrachialis	Shoulder flexion and adduction

Stabilizers 11

Stabilizers in the push-up, with what each does
Muscle	What it does here
Rectus abdominis	Stopping the hips sagging
External oblique	Stopping the hips sagging
Internal oblique	Stopping the hips sagging
Transversus abdominis	Raising abdominal pressure to stiffen the trunk
Iliopsoas	Holding the hips in line
Quadriceps	Keeping the knees straight and the hips in line
Gluteus maximus	Keeping the pelvis level with the trunk
Supraspinatus	Holding the head of the humerus in its socket
Infraspinatus	Holding the head of the humerus in its socket
Teres minor	Holding the head of the humerus in its socket
Subscapularis	Holding the head of the humerus in its socket

Lowering and lifting

What the prime movers of the push-up do in each half of a rep
Phase	What the prime movers do
Lowering	Pectoralis major, the anterior deltoid and triceps lengthen as the chest drops
Pushing	They shorten to press the body back up

Where these prime movers also work

The sternal part of pectoralis major: prime mover in the flat bench press and parallel-bar dip; synergist in the incline bench press, pull-up, chin-up and lat pulldown.
The clavicular part of pectoralis major: prime mover in the flat bench press, incline bench press and standing overhead press; synergist in the parallel-bar dip.
The anterior deltoid: prime mover in the flat bench press, incline bench press, parallel-bar dip and standing overhead press; synergist in the dumbbell lateral raise.
Triceps brachii: prime mover in the flat bench press, incline bench press, parallel-bar dip, standing overhead press and cable triceps pushdown.

Compared with the other horizontal push lifts

Flat bench press: the same prime movers; synergists only here, serratus anterior; stabilizers only here, rectus abdominis, external oblique, internal oblique, transversus abdominis, iliopsoas, the quadriceps and gluteus maximus; stabilizers only in the flat bench press, serratus anterior, biceps brachii, latissimus dorsi, the rhomboids, the middle trapezius, the wrist and finger flexors, and the wrist and finger extensors.
Incline bench press: prime movers in both, the clavicular part of pectoralis major, the anterior deltoid and triceps brachii; prime movers only here, the sternal part of pectoralis major.

Sources

NSCA, Essentials of Strength Training and Conditioning, 4th ed. (2016)
Neumann, Kinesiology of the Musculoskeletal System, 3rd ed. (2017)

The cited studies that measured muscle activity used electromyography, and a larger signal need not mean more force or more growth (Vigotsky et al. (2018), Front Physiol 8:985). The roles draw on those studies for which muscles a lift involves and how two lifts differ, never to rank one muscle against another.

See these muscles in 3D

Visualiser · Biology Muscles Worked by Exercise 3D Explorer Choose a lift and a real body lights its prime movers, synergists and stabilisers, front and back, with the same muscles in 3D. Visualiser · Biology Muscle Origin, Insertion and Action Explorer Paint a muscle’s origin and insertion on real 3D bones, or click a bone to see what attaches to it.