The leg curl is the go-to isolation exercise for the hamstrings — a machine knee-flexion, done lying or seated, that targets the back of the thigh directly. Here's how to do it with good form, the muscles it works, the mistakes to avoid, and how to program it.
The leg curl is a machine isolation exercise that targets the hamstrings — the three muscles on the back of the thigh. You lie face-down or sit in the machine with a pad above your heels and bend your knees to curl the pad in, then lower under control. It isolates the hamstrings' knee-flexion role directly, making it a simple way to add hamstring volume alongside hip-hinge lifts like the Romanian deadlift.
The leg curl is an isolation exercise built around knee flexion. The hamstrings do all of the work — the biceps femoris, semitendinosus and semimembranosus — with the calves assisting slightly at the knee.
| Role | Muscles | What they do in the lift |
|---|---|---|
| Primary mover | Hamstrings (all three) | Flex the knee to curl the pad toward the glutes |
| Outer hamstring | Biceps femoris | Contributes to knee flexion on the outside of the thigh |
| Inner hamstrings | Semitendinosus, semimembranosus | Contribute on the inside of the back of the thigh |
| Assisting | Gastrocnemius (calf) | Helps flex the knee, especially with toes pointed toward the shin |
Step-by-step form for the machine leg curl, lying or seated. Setting the pads correctly is what makes the movement feel right.
If you want to train the hamstrings with a different emphasis or equipment, these are the common swaps:
Want the hip-hinge and bodyweight hamstring options the leg curl complements? Compare it with the Romanian deadlift and the Nordic curl.
The leg curl works best as an accessory alongside a hip-hinge movement. General starting points:
| Goal | Sets × reps | Notes |
|---|---|---|
| Hamstring size | 2–4 × 8–15 | Controlled tempo, full range, take the last set close to failure |
| Pump / finisher | 2–3 × 12–15 | Lighter load, short rest, squeeze at the top of each curl |
| Frequency | 1–2× / week | Progress by adding a rep or a little load when you hit the top of the range |
Want a full structured plan that includes hamstring accessory work? See Push Pull Legs, and read up on RPE to gauge how hard each set should feel.
Log every leg curl set — weight, reps, and an RPE value — in LiftHero, and it charts your progressive overload and flags personal records so you can see your hamstring work climbing over the weeks. You can add warm-up sets, supersets and rest-timer holds, then drop the exercise into a saved routine so it's ready the next time you train. LiftHero records what you log; it doesn't diagnose your form.
It targets the hamstrings — the biceps femoris, semitendinosus and semimembranosus on the back of the thigh. The calves assist slightly at the knee.
Both work well and slightly differently. The seated curl places the hip in flexion for more hamstring stretch, while the lying curl works them in a more neutral hip position. Either, or both, is fine.
Not strictly, but they complement hip-hinge work. The Romanian deadlift trains the hamstrings at the hip, while the leg curl trains their knee-flexion role directly, so together they cover both functions.
Hamstring cramping is common and usually harmless. It often eases if you warm up first, use a lighter load, point the toes toward your shins, and avoid jerking into the top of the rep.
As an isolation accessory, about 8–15 reps across 2–4 sets taken close to failure. Most lifters use them once or twice per week alongside a hip-hinge movement.
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This guide is educational and not medical advice. Consult a qualified coach or medical professional before starting or changing a training program.
By Meitar Lazimi, founder of LiftHero · Last updated July 9, 2026.