The hamstring curl is a machine isolation exercise that trains knee flexion against resistance. Lie or sit on the machine, hook your heels over the pad, and curl your legs toward your glutes — moving only at the knee, with your hips pressed flat.
Isolates the hamstrings, useful for building muscle balance between the front and back of the leg.
The hamstring curl isolates knee flexion — the hamstrings' job of bending the knee. The hamstring group is three muscles: the biceps femoris on the outside, and the semitendinosus and semimembranosus on the inside. All three cross the knee, and the leg curl loads every one of them through a range that hip-hinge movements barely touch.
That matters because the hamstrings have two jobs: they flex the knee and they extend the hip. Romanian deadlifts and good mornings train the hip-extension job hard but leave knee flexion almost untouched. If your only hamstring work is hinging, you're training half the muscle. The leg curl fills that gap — which is why it earns a place in a program even if you already deadlift heavy.
The calves assist slightly (the gastrocnemius also crosses the knee), and the glutes stay contracted to keep the hips down. But if you feel the rep anywhere other than the back of your thigh, the setup has drifted — see common mistakes.
Lifting the hips off the pad. Arching the lower back and letting the hips rise lets you swing heavier weight, but it shifts load off the hamstrings and compresses the lumbar spine. Fix: press your hips flat into the pad for the entire set and drop the weight until you can keep them there.
Using momentum. Kicking the pad up fast and letting it drop turns a strength exercise into a swing. The hamstrings get the least stimulus exactly where they should get the most — the eccentric. Fix: take 2–3 seconds lowering every rep, under control, with no bounce at the bottom.
Cutting the range short. Stopping halfway up, or failing to fully straighten the legs between reps, removes both the peak contraction and the loaded stretch. Fix: curl until the pad nearly touches your glutes, then extend fully before the next rep.
Pointing your toes. With the feet plantarflexed (toes pointed), the gastrocnemius shortens and starts sharing the load — you'll feel it cramp in the calves. Fix: keep the feet in dorsiflexion (toes pulled toward your shins) the whole set so the hamstrings do the work.
Going too heavy. The hamstrings are prone to cramping and strain when overloaded on an isolation machine. If your form breaks on rep 6 of a 12-rep set, the weight is wrong. Add load only when every rep is clean.
For hypertrophy, 3–4 sets of 10–12 reps with 60–90 seconds rest, with a deliberate 3-second eccentric on every rep. The hamstrings respond well to controlled lowering — the eccentric is where most growth and most injury-resistance is built. For strength-flavored work, drop to 6–8 reps with heavier load and 90–120 seconds rest.
Place the leg curl after your heavy hip-hinge work (Romanian deadlifts, deadlifts) on a leg or pull day, not before — you don't want pre-fatigued hamstrings under a loaded bar. A total hamstring volume of 8–14 working sets per week suits most lifters, split between a knee-flexion movement like this and a hip-hinge movement.
Seated or lying? If your gym has both, favor the seated leg curl. A 2021 study by Maeo and colleagues found roughly twice the biceps femoris growth from the seated version over 12 weeks at matched volume — the hip-flexed position loads the hamstring in a stretched position, which drives more stimulus per set. The lying version still works; it's just a slightly smaller return per set.
No leg curl machine? The closest alternatives keep knee flexion in the movement. A Nordic curl — kneeling with your feet anchored, lowering your torso under hamstring control — is the most demanding bodyweight option and brutally effective. A swiss-ball or sliding leg curl scales the same pattern down. Neither needs a machine.
If you only have free weights, the Romanian deadlift and glute bridge train the hamstrings hard — but through hip extension, not knee flexion. They're not direct substitutes; ideally you keep one of each pattern in the program.
Unlike most hamstring exercises, the leg curl puts almost no load on the spine, which makes it a useful option when your lower back is fried from heavy hinging. If a tweaked back has you avoiding deadlifts, the leg curl lets you keep training hamstrings while you recover.
Common questions about form, safety, equipment, and alternatives for this exercise.
The hamstring curl isolates the hamstrings — the biceps femoris, semitendinosus, and semimembranosus on the back of the thigh — through knee flexion. The calves assist slightly because the gastrocnemius also crosses the knee, and the glutes stay contracted to keep the hips down. The machine removes hip movement, so the hamstrings do nearly all the work.