The romanian deadlift and the stiff leg deadlift look nearly identical. You hinge, you grip, you lower, you stand. The only visible difference — a slight bend in the knee — seems like a footnote, not a decision that changes anything. So when you ask which one is better for your hamstrings, you expect one clean answer.
You won’t get one. Because “your hamstrings” is doing something sneaky in that question — pretending to be one muscle when it’s actually several, and they disagree.
Romanian Deadlift vs Stiff Leg Deadlift: What the Muscles Actually Show
The romanian deadlift and stiff leg deadlift target different muscles despite looking nearly identical. The inner hamstring (semitendinosus) responds more to the RDL, the glutes respond more to the stiff leg deadlift, and the outer hamstring (biceps femoris) shows no measurable difference between the two — your choice depends on which muscle you’re prioritizing.
— Coratella et al. 2022 · Int J Environ Res Public Health · n=10
When researchers measured exactly which muscles fired during each lift in trained bodybuilders, the answer didn’t come back as a single verdict. It came back as a split decision — with one result nobody saw coming.
The medial hamstring — the semitendinosus, running along the inner back of your thigh — worked considerably harder during the romanian deadlift. If you’ve ever heard someone say RDLs are “the hamstring exercise,” this muscle is the reason. The romanian deadlift’s slight knee bend shifts the movement toward a knee-dominant action, and the semitendinosus responds to it.
Now the part that upends the entire conversation. The biceps femoris — the muscle on the outer back of your thigh, the one that comes to mind first when someone says “hamstrings” — showed no difference whatsoever between the two exercises. In practical terms: pick either one for this muscle. It genuinely does not care which deadlift you chose.
Every competitor article on the internet will tell you one of these exercises targets “the hamstrings” more. None of them mention this finding. Because none of them separate the hamstring into its actual parts — and the part most lifters think of first doesn’t pick a side.
Then there’s the answer nobody asked for. The gluteus maximus — your largest glute muscle — responded more to the stiff leg deadlift. Lock your knees and the movement becomes pure hip extension, shifting load away from the semitendinosus and onto the glutes. A comparison about hamstrings quietly turned into a glute finding too.
The variable underneath all three results is the same: knee position. Bend slightly and the load favors the inner hamstring. Straighten and the load transfers to the glutes. The outer hamstring sits between these two patterns and responds to both equally — which is exactly why it doesn’t care.
Inner hamstring emphasis: The romanian deadlift. The semitendinosus responds to that slight knee bend.
More glute from your hinge: The stiff leg deadlift. Extended knees shift the load to pure hip extension.
Outer hamstring (biceps femoris): Either exercise. This muscle does not distinguish between them.
One honest caveat worth naming: this data measures muscle activation — how hard each muscle fires during the movement — not long-term growth directly. And it comes from competitive bodybuilders lifting at high intensity. Whether the same per-muscle split holds for less experienced lifters hasn’t been tested head-to-head. The pattern is clear in this population. Its universality hasn’t been confirmed beyond that group — something the researchers themselves flag.
So the answer to “which is better” refuses to be singular. Inner hamstring emphasis — the romanian deadlift earns that. More glute involvement from your posterior chain work — the stiff leg deadlift takes it. And the outer hamstring you’ve been agonizing over — either exercise, same result. The choice only matters for two of the three muscles, and the principle that exercise choice determines where growth lands explains why.
That points somewhere your original search didn’t expect: if two exercises that look nearly identical split the posterior chain this differently, what does your choice of leg curl versus RDL mean for full hamstring coverage?