Romanian deadlift muscles worked

Every role here is for this technique: from standing, knees slightly bent and kept there, the bar lowered to just below the knees by pushing the hips back, back flat.

What muscles does the Romanian deadlift work?

The prime movers of the Romanian deadlift are the hamstrings, gluteus maximus, adductor magnus and the erector spinae. They produce hip extension and hold the spine extended. No muscle assists as a synergist. Eleven stabilizers hold joints and segments still, among them the quadriceps, gastrocnemius and multifidus. The roles follow Schoenfeld et al. (2015), Ebben (2009) and NSCA (2016).

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Joint actions and their prime movers

The joint actions of the Romanian deadlift and the prime movers that produce each
Joint action	Prime movers
Hip extension	The hamstrings, gluteus maximus and adductor magnus
Holding the spine extended	The erector spinae

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 Romanian deadlift, with what each does
Muscle	What it does here
Hamstrings	Hip extension, from a long, loaded stretch
Gluteus maximus	Hip extension
Adductor magnus	Hip extension
Erector spinae	Keeping the spine from rounding as the trunk tips forward, without changing length

Stabilizers 11

Stabilizers in the Romanian deadlift, with what each does
Muscle	What it does here
Quadriceps	Holding the knees at a slight bend
Gastrocnemius	Steadying the knee and ankle
Multifidus	Stiffening each lumbar segment
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
Latissimus dorsi	Keeping the bar close to the legs
Upper trapezius	Holding the shoulder girdle up against the bar’s pull
Rhomboids	Holding the shoulder blades back
Wrist and finger flexors	Gripping the bar

Lowering and lifting

What the prime movers of the Romanian deadlift do in each half of a rep
Phase	What the prime movers do
Lowering	The hamstrings and gluteus maximus lengthen as the hips go back
Rising	They shorten to bring the hips through

The erector spinae hold without changing length, though they are prime movers rather than stabilizers.

Where these prime movers also work

The hamstrings: prime mover in the conventional deadlift, sumo deadlift and lying leg curl; synergist in the back squat, front squat, leg press, barbell hip thrust, Bulgarian split squat and walking lunge.
Gluteus maximus: prime mover in the back squat, front squat, leg press, conventional deadlift, sumo deadlift, barbell hip thrust, Bulgarian split squat and walking lunge.
Adductor magnus: prime mover in the back squat, front squat, leg press, conventional deadlift, sumo deadlift, Bulgarian split squat and walking lunge; synergist in the barbell hip thrust.
The erector spinae: prime mover in the conventional deadlift and sumo deadlift.

Compared with the other hinge lifts

Conventional deadlift: prime movers in both, gluteus maximus, the hamstrings, adductor magnus and the erector spinae; prime movers only in the conventional deadlift, the quadriceps.
Sumo deadlift: prime movers in both, gluteus maximus, adductor magnus, the hamstrings and the erector spinae; prime movers only in the sumo deadlift, the quadriceps.
Barbell hip thrust: prime movers in both, gluteus maximus; prime movers only here, the hamstrings, adductor magnus and the erector spinae.

Sources

Schoenfeld et al. (2015), J Strength Cond Res 29(1):159
Ebben (2009), Int J Sports Physiol Perform 4(1):84
NSCA, Essentials of Strength Training and Conditioning, 4th ed. (2016)

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.