How to Do It
- Adjust the machine so your knee joint lines up with its pivot and the roller rests just above your heel or Achilles tendon.
- On a seated machine, secure the thigh pad; on a lying machine, keep your hips and torso in contact with the pads.
- Brace lightly and start with the legs extended only as far as the machine and your control allow.
- Curl the roller toward your body without lifting your hips or twisting, stopping at a comfortable end range.
- Lower the weight smoothly, keeping tension and alignment rather than letting the stack drop.
Technique
- Use a load that lets you keep the pelvis, thigh pad, and torso stable on every repetition.
- The hamstrings are the target; the gastrocnemius can assist, but it is not the main reason to program the curl.
Key Cues
- Knee on the pivot.
- Roller above the heel.
- Hips stay down.
- Control the lowering phase.
Common Mistakes
- Misaligning the knee with the machine pivot.
- Placing the roller on the calf instead of just above the heel.
- Letting the hips lift or the torso shift to finish a heavy repetition.
- Rushing the eccentric or forcing a range the machine position does not allow you to control.
- Using more load than you can move without losing pad contact.
The leg curl is a single-joint hamstring exercise. Set the knee pivot correctly, keep the pelvis and torso fixed, and lower each repetition under control. This guide covers both seated leg curls and lying machines, then helps you choose between them without claiming that one is universally mandatory.
Machine Setup Checklist
| Check | What to look for |
|---|---|
| Knee pivot | Your knee lines up with the machine’s pivot. |
| Roller | It sits just above the heel or Achilles tendon, not high on the calf. |
| Thigh or torso pad | The pad keeps you secure without forcing an uncomfortable position. |
| Pelvis and torso | They stay in contact with the support throughout the set. |
| Range | You can curl and lower without losing alignment or control. |
Muscles Worked by the Leg Curl
Leg curls primarily train the hamstrings through knee flexion. The gastrocnemius can assist because it crosses the knee, but it is not the target. A curl complements a Romanian deadlift because the main joint action differs: the curl emphasizes knee flexion, while the hinge emphasizes hip extension. See the hamstring exercises hub for the wider movement menu.
Seated vs Lying Leg Curl
| Decision | Seated leg curl | Lying leg curl |
|---|---|---|
| Hip position | Flexed | More extended |
| Hamstring starting length | Generally longer for biarticular hamstrings | Generally shorter |
| Setup priority | Thigh pad and knee-pivot alignment | Pelvis staying on pad and knee-pivot alignment |
| Evidence wording | One 12-week within-person trial found greater hamstring growth | The same trial still found growth; it was not ineffective |
| Practical choice | Prefer if comfortable and available | Use when it fits you or the equipment better |
The 12-week within-person trial reported greater hamstring hypertrophy with seated curls while both variations produced growth. That is useful comparison evidence, not a guarantee that seated curls will be superior for every person or machine.
Sets, Reps, and Progression
| Goal | Working sets | Reps | Effort and progression |
|---|---|---|---|
| Strength-oriented accessory | 3–4 | 6–10 | Stop with controlled reps remaining; add load after reaching the top of the range. |
| Hypertrophy | 3–4 | 8–15 | Keep hips fixed and the lowering phase controlled; add reps, then load. |
| Endurance / technique | 2–3 | 15–20 | Use a load that preserves alignment and range. |
These are practical programming ranges, not direct numerical conclusions from one trial. Start with the leg day workout volume that fits your week, add repetitions before the smallest plate increment, and track the machine and settings.
Leg Curl Alternatives
- Romanian deadlift: a hip-hinge alternative for hamstrings and glutes.
- Dumbbell Romanian deadlift: a dumbbell version of the hinge.
- Nordic curl: a demanding bodyweight knee-flexion option.
- Band or cable curl: a knee-flexion substitute when a leg-curl machine is unavailable.
- Leg extension: an agonist/antagonist contrast that trains knee extension rather than knee flexion.
Evidence and Editorial Scope
The comparison evidence is a single 12-week within-person trial, and programming guidance is aligned with the exercise methodology and current ACSM resistance-training guidance. This page does not make pain, rehabilitation, injury-prevention, or diagnostic claims.
Alternatives
- Romanian Deadlift: Trains the hamstrings through hip extension rather than knee flexion.
- Dumbbell Romanian Deadlift: A hinge alternative when a barbell is unavailable.
- Leg Extension: A contrasting knee-extension exercise for the quadriceps.
References
- Anaerobic and Muscle Endurance Development: Lifting Guidelines. National Strength and Conditioning Association (2017)Back to claim
- American College of Sports Medicine Position Stand. Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults: An Overview of Reviews. Medicine & Science in Sports & Exercise (2026)Back to claim
- Updating ACSM's Recommendations for Exercise Preparticipation Health Screening. Medicine & Science in Sports & Exercise (2015)Back to claim
- Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths. Medicine & Science in Sports & Exercise (2021)Back to claim
- American College of Sports Medicine Position Stand. Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults: An Overview of Reviews. Medicine & Science in Sports & Exercise (2026)Back to claim
See our exercise methodology for how this evidence is applied and its limits.
Frequently Asked Questions
- What muscles do leg curls work?
- Leg curls primarily train the hamstrings by bending the knee. The calf can assist, but the hamstrings are the target; pair curls with a hip hinge such as an RDL to train the hamstrings in a second movement pattern.
- Are seated or lying leg curls better?
- Both can build the hamstrings. One 12-week within-person study found greater hypertrophy from seated curls, likely because the biarticular hamstrings began at longer lengths, but comfort, setup, and equipment availability still matter.
- How many leg curls should I do?
- A practical starting point is 2–4 working sets of 8–15 controlled repetitions, adjusted for the rest of the week's hamstring work. Add repetitions before increasing the weight when form remains stable.
- Why do my hips lift during leg curls?
- The load may be too heavy, the machine may be misaligned, or the available range may exceed what you can control. Reduce the load or range and keep the pelvis in contact with the pad; do not turn this into a pain-treatment answer.
- What is a good leg curl alternative?
- Romanian deadlifts train the hamstrings through hip extension, while Nordic curls and banded or cable curls preserve knee flexion. The best substitute depends on whether the program needs a hinge or a curl pattern.