Romanian deadlifts do work your abs, but not in the way crunches or sit-ups do. Your abdominal muscles fire throughout every rep to stabilize your spine while your hips hinge under load. This makes the RDL a legitimate core exercise, even though you’ll never feel the burning sensation of a direct ab movement. The American Council on Exercise describes the RDL as “a dynamic version of the plank,” where the deep muscles of the spine contract to maintain stability while the hips move through flexion and extension.
Which Ab Muscles Fire During RDLs
Your core has two functional layers, and the RDL engages both. The deep layer includes the transversus abdominis, a corset-like muscle that wraps around your midsection and generates intra-abdominal pressure to protect your spine. The internal obliques sit alongside it and co-contract to keep your trunk rigid. These muscles are classified as “local” stabilizers, meaning their primary job is locking the spine in place rather than producing movement.
The outer layer includes the rectus abdominis (your “six-pack” muscle) and the external obliques. These are “global” muscles designed to control and produce movement, like bending or rotating your torso. During an RDL, they contribute to bracing but aren’t the primary drivers. You won’t get significant shortening or lengthening of the rectus abdominis the way you would during a crunch, which is why RDLs don’t produce that deep ab burn. Their role is isometric: holding position against the pull of gravity on the barbell.
The full list of stabilizers active during a hip hinge includes the transversus abdominis, internal and external obliques, the muscles along the spine (multifidi and erectors), and the lats. All of these contract together to form a rigid cylinder around your spine while your hips do the actual moving.
How RDLs Compare to Direct Core Exercises
The honest answer is that RDLs train your abs differently than exercises built specifically for core activation, and neither type fully replaces the other. Exercises like planks, dead bugs, side planks, and bird dogs are designed to maximize how hard the deep core muscles contract. Research using ultrasound imaging shows that these exercises can increase transversus abdominis thickness by 75 to 100 percent above resting levels, depending on the exercise and bracing technique used. Side planks and bird dogs tend to rank highest for internal oblique activation, while dead bugs excel at engaging the deeper transversus abdominis.
RDLs generate core activation through a different mechanism: the need to stabilize a heavy external load while your torso is in a vulnerable forward-leaning position. The heavier the weight, the harder your abs work to prevent your spine from rounding. This type of anti-flexion demand is functional and builds the kind of core strength that transfers to sports, lifting, and daily activities like picking things up off the floor. But the activation pattern is reflexive and submaximal. Your abs are working, just not as their primary focus.
Think of it this way: a plank is a core exercise that happens to involve your shoulders. An RDL is a hip and hamstring exercise that happens to involve your core. Both train your abs, but the intensity and emphasis are different.
How to Maximize Core Engagement During RDLs
The biggest factor in how much your abs work during RDLs is whether you’re bracing properly. Proper bracing isn’t just “tightening your stomach.” It involves a specific breathing pattern that builds pressure from the inside out.
Place your hands on your abdomen and take a deep breath directed into your belly, not your chest. You should feel your abdomen press outward into your hands. Your chest should not rise. Once your midsection is inflated, contract your ab muscles around that air pocket to lock everything in place. This creates intra-abdominal pressure, essentially turning your core into a pressurized column that supports your spine from the inside. Hold this brace throughout the lowering and lifting phase of each rep, then reset your breath at the top.
If you’re new to this technique, practice it without any weight first. Try 10 repetitions of the brace with a 10-second hold each to build the coordination before applying it to your RDLs. Once bracing becomes automatic, you’ll notice your core feels far more engaged during hip hinge movements.
A few other factors influence how hard your abs work during RDLs:
- Load: Heavier weight demands more stabilization. Light RDLs with dumbbells won’t challenge your core much. Barbell RDLs at a working weight will.
- Single-leg variations: A single-leg RDL adds a rotational challenge, forcing your obliques to work harder to keep your hips and shoulders square.
- Tempo: Slowing down the lowering phase increases time under tension for your stabilizers, including your abs.
Can RDLs Replace Ab Training?
RDLs provide meaningful core work, but they won’t build visible abs on their own. The rectus abdominis needs direct training through flexion-based or anti-extension exercises to grow in size. Movements like hanging leg raises, cable crunches, or ab wheel rollouts target the rectus abdominis through a full range of motion, which RDLs simply don’t provide.
Where RDLs shine is in building the deep stabilizing strength that protects your spine and improves performance in other lifts. If your goal is a strong, functional core that keeps you safe under heavy loads, RDLs are one of the best exercises in your program. If your goal is visible ab definition, you’ll want dedicated core training alongside them. The two aren’t competing approaches. They complement each other, training different layers of the same muscle group for different purposes.