Flat bench press muscles worked

Every role here is for this technique: lying on a flat bench, grip about one and a half shoulder widths, bar lowered to the lower chest and pressed to straight arms.

What muscles does the flat bench press work?

The prime movers of the flat bench press are both parts of pectoralis major, the anterior deltoid and triceps brachii. They produce shoulder horizontal adduction and elbow extension. The one synergist is coracobrachialis. Eleven stabilizers hold joints and segments still, among them serratus anterior, supraspinatus and infraspinatus. The roles follow Barnett et al. (1995), Lehman (2005) and Neumann (2017).

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Joint actions and their prime movers

The joint actions of the flat bench press 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 flat bench press, with what each does
Muscle	What it does here
Pectoralis major, sternal part	Bringing the upper arm across the chest
Pectoralis major, clavicular part	Bringing the upper arm across and up
Anterior deltoid	Shoulder flexion and horizontal adduction
Triceps brachii	Elbow extension, all three heads

Synergists 1

Synergists in the flat bench press, with what each does
Muscle	What it does here
Coracobrachialis	Shoulder flexion and adduction

Stabilizers 11

Stabilizers in the flat bench press, with what each does
Muscle	What it does here
Serratus anterior	Holding the shoulder blade against the ribs
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
Biceps brachii	Steadying the elbow and the front of the shoulder
Latissimus dorsi	Controlling the bar path and the upper arm
Rhomboids	Keeping the shoulder blades pulled together on the bench
Middle trapezius	Keeping the shoulder blades pulled together on the bench
Wrist and finger flexors	Gripping the bar
Wrist and finger extensors	Holding the wrist straight under the bar

Lowering and lifting

What the prime movers of the flat bench press do in each half of a rep
Phase	What the prime movers do
Lowering	Pectoralis major, the anterior deltoid and triceps lengthen under the bar
Pressing	They shorten to drive the bar up

Where these prime movers also work

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

Compared with the other horizontal push lifts

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.
Push-up: the same prime movers; synergists only in the push-up, serratus anterior; stabilizers only here, serratus anterior, biceps brachii, latissimus dorsi, the rhomboids, the middle trapezius, the wrist and finger flexors, and the wrist and finger extensors; stabilizers only in the push-up, rectus abdominis, external oblique, internal oblique, transversus abdominis, iliopsoas, the quadriceps and gluteus maximus.

Sources

Barnett, Kippers and Turner (1995), J Strength Cond Res 9(4):222
Lehman (2005), J Strength Cond Res 19(3):587
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.