Leg press muscles worked

Every role here is for this technique: 45 degree sled, back flat on the pad, feet shoulder-width in the middle of the platform, knees to about 90 degrees.

What muscles does the leg press work?

The prime movers of the leg press are the quadriceps, gluteus maximus and adductor magnus. They produce knee extension and hip extension. The one synergist is the hamstrings. Eight stabilizers hold joints and segments still, among them soleus, gastrocnemius and gluteus medius. The roles follow NSCA (2016) and Neumann (2017).

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Joint actions and their prime movers

The joint actions of the leg press and the prime movers that produce each
Joint action	Prime movers
Knee extension	The quadriceps
Hip extension	Gluteus maximus and adductor magnus

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 3

Prime movers in the leg press, with what each does
Muscle	What it does here
Quadriceps	Knee extension, all four heads
Gluteus maximus	Hip extension
Adductor magnus	Hip extension

Synergists 1

Synergists in the leg press, with what each does
Muscle	What it does here
Hamstrings	Hip extension

Stabilizers 8

Stabilizers in the leg press, with what each does
Muscle	What it does here
Soleus	Holding the ankle against the platform
Gastrocnemius	Holding the ankle against the platform
Gluteus medius	Keeping the knees in line with the feet
Rectus abdominis	Bracing the trunk against the load
External oblique	Bracing the trunk and resisting rotation
Internal oblique	Bracing the trunk and resisting rotation
Transversus abdominis	Raising abdominal pressure to stiffen the trunk
Wrist and finger flexors	Gripping the handles to stay in the seat

Lowering and lifting

What the prime movers of the leg press do in each half of a rep
Phase	What the prime movers do
Lowering	The quadriceps and gluteus maximus lengthen as the sled comes down
Pressing	They shorten to push the sled away

Where these prime movers also work

The quadriceps: prime mover in the back squat, front squat, conventional deadlift, sumo deadlift, Bulgarian split squat, walking lunge and leg extension; synergist in the barbell hip thrust and front plank.
Gluteus maximus: prime mover in the back squat, front squat, conventional deadlift, sumo deadlift, Romanian deadlift, barbell hip thrust, Bulgarian split squat and walking lunge.
Adductor magnus: prime mover in the back squat, front squat, conventional deadlift, sumo deadlift, Romanian deadlift, Bulgarian split squat and walking lunge; synergist in the barbell hip thrust.

Compared with the other squat lifts

Back squat: the same prime movers; synergists only in the back squat, soleus; stabilizers only here, soleus, gastrocnemius, and the wrist and finger flexors; stabilizers only in the back squat, the erector spinae, multifidus, quadratus lumborum, gluteus minimus, the upper trapezius, the middle trapezius and the rhomboids.
Front squat: the same prime movers; synergists only in the front squat, soleus; stabilizers only here, soleus, gastrocnemius, and the wrist and finger flexors; stabilizers only in the front squat, the erector spinae, multifidus, gluteus minimus, the anterior deltoid and the upper trapezius.

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.