Nordic curl vs stiff-leg deadlift: which grows your hamstrings?

Which muscles work on the Nordic and the stiff-leg deadlift?

Your hamstrings, behind your thigh, are three muscles: the biceps femoris on the outside, the semitendinosus and the semimembranosus on the inside. They start on your ischium, the pelvic bone you sit on, and attach just below your knee. They bend your knee, that’s knee flexion, and straighten your hip, that’s hip extension (Marrero et al., 2025).

The two exercises load them from different ends. On the Nordic, kneeling with your ankles anchored, you tip forward, body straight, braking all the way to the floor: your knee does the work. On the stiff-leg deadlift, you hinge your torso forward, knees nearly straight, then stand back up: your hip does. One leans on knee flexion, the other on hip extension (Boyer et al., 2021).

Nordic or stiff-leg deadlift: which grows your hamstrings?

One blinded study compared them head to head. In it, 36 people who didn’t lift were randomly split into three groups: Nordic, stiff-leg deadlift, or nothing. The first two groups trained three times a week for 9 weeks, and the volume of each of the three muscles was measured with ultrasound (Morin et al., 2025).

The Nordic mostly grew the semitendinosus: +24%. The stiff-leg deadlift mostly grew the semimembranosus: +11%, with big differences from one person to the next. Neither exercise targeted the biceps femoris. A second paper on the same people adds that the hamstrings as a whole grew comparably in both groups: +11.4% with the Nordic, +7% with the stiff-leg deadlift (Morin et al., 2025).

Limits: a single study, of 36 people who didn’t lift, over 9 weeks.

Why does each exercise grow a different muscle?

One lead: they don’t share out the effort the same way. In 20 people, the stiff-leg deadlift gave the semimembranosus a bigger share of the effort than the semitendinosus in 18 of them, and the Nordic did the reverse in 19 (Boyer et al., 2021). That’s electrical activity measured through the skin, not growth, and the most active muscle varied from person to person.

A computer model from the same Nantes team explains part of it: on the Nordic, the semitendinosus works at a longer length and produces more force than its neighbors, which matches its growth. On the stiff-leg deadlift, the model doesn’t explain why the semimembranosus pulls ahead: the reason is still open (Morin et al., 2026).

Do other studies agree?

Partly. In 36 young men, 12 of whom didn’t train, 10 weeks of stiff-leg deadlifts, doing only the lowering phase, grew the semimembranosus: +5.7% at two sessions a week, +7.4% at three (Kawama et al., 2024).

But the knee-or-hip rule isn’t absolute: in 30 recreational athletes, on MRI, 10 weeks of hip extensions grew the semitendinosus about as much as the Nordic, and the long head of the biceps femoris more (Bourne et al., 2017).

And another team saw no difference at all. In 32 students aged 20 on average, who already had some lifting experience, 6 weeks of Romanian deadlifts, another exercise where the hip does the work, or Nordic curls, twice a week, increased hamstring cross-sectional area by about 10% on ultrasound, just as much with either one (Crawford et al., 2025). The authors point out that their study was shorter, and that a muscle’s cross-section, measured at three spots, isn’t its whole volume.

Should you do both?

Yes, and for your strength too. In the Nantes study, the one-rep max rose 37% on the Nordic and 34% on the stiff-leg deadlift, each on its own exercise (Morin et al., 2025). But it carried over less well to the other one: the Nordic group gained only 11% on the stiff-leg deadlift, the stiff-leg deadlift group 21% on the Nordic, and the authors advise putting both exercises in the same program (Morin et al., 2025).

Only one hamstring exercise in your plan? It’s not one exercise your hamstrings need: it’s one for the knee, one for the hip.