Leg Curl: How to Do It, Muscles Worked and Home Alternatives

The leg curl is the simplest hamstring exercise there is: you bend your knee against resistance, and the muscles on the back of your thigh do the work. It has a reputation as a machine-gym accessory, the thing you do at the end of leg day when the squat rack is busy, and that reputation sells it short. The leg curl trains a job your deadlifts and squats barely touch, and one part of your hamstrings gets almost nothing without it. Here is how to do it properly, what it actually works, and how to get the same effect at home without a machine.

How to do a leg curl

The setup matters more than the weight. Most bad leg curls are bad because the machine is not adjusted to the person using it.

1. Line up the knee. Set the machine so your knee joint sits directly in line with the pivot of the lever arm. This is the single most important adjustment. If your knee is in front of or behind the pivot, the load fights your joint instead of your muscle.
2. Set the pad. The ankle pad should rest just above your heel, on the back of your ankle, not on your calf and not on your Achilles.
3. Lock yourself down. On a seated machine, pull the thigh pad down snug so your legs cannot lift. On a lying machine, grip the handles and keep your hips pressed into the bench.
4. Curl. Bend your knees and bring your heels towards your backside, squeezing the hamstrings at the end. Take about one second to lift.
5. Lower slowly. Take three seconds to return to the start, resisting the whole way. Stop just short of the weight stack touching down so the tension stays on.

Muscles worked

The leg curl is one of the few exercises that trains the hamstrings through knee flexion rather than hip extension, and that distinction is the whole reason it earns a place in your programme.

• Biceps femoris (long head). The outer hamstring, and the one most often injured in sprinting. It crosses both the hip and the knee, so it works in leg curls and in deadlifts.
• Biceps femoris (short head). This is the important one. It only crosses the knee, so it is the one muscle in the group that hip hinges cannot reach. Without knee flexion work, it is undertrained.
• Semitendinosus and semimembranosus. The inner hamstrings, which drive the curl alongside the biceps femoris. The balance between inner and outer hamstring activity shifts depending on whether you are curling or hinging (task dependent differences in hamstring EMG during leg curls and hip extensions).
• Gastrocnemius. The upper calf crosses the back of the knee, so it assists on every rep. This is why toe position changes how a leg curl feels.

The practical takeaway is that leg curls and Romanian deadlifts are not interchangeable. Hip-dominant exercises tend to load the biceps femoris long head hard, while the lying leg curl produces the highest hamstring-to-quadriceps activation ratio of the common lower body lifts (hamstring-to-quadriceps activation ratio during lower-limb strengthening exercises). If you want complete hamstrings, do both.

Seated or lying?

Both work, but they are not identical.

The seated leg curl keeps your hips flexed at around 90 degrees, which pre-stretches the hamstrings before you even start the rep. Since the hamstrings cross the hip as well as the knee, that hip position means they are working from a longer starting length, and muscles trained at long lengths tend to grow more. If your gym has both, this is the one to prioritise.

The lying leg curl has your hips straight, so the hamstrings start shorter. It is still a perfectly good exercise, and many people find the position more comfortable. Its main quirk is that it is easy to cheat by letting your hips lift off the bench, which turns the movement into a partial hip extension.

There is also the standing leg curl, done one leg at a time, which is useful for spotting and fixing a strength difference between your legs.

Common mistakes

• Lifting your hips. On a lying curl, when the weight gets heavy your hips rise off the pad and your lower back arches. That is your body borrowing hip extension to finish a rep your hamstrings could not. Drop the weight.
• Going too heavy to control the lower. The lowering phase is where most of the benefit sits. If the stack crashes down, you are throwing away the best part of the exercise.
• Bad knee alignment. Covered above, but worth repeating, because this is what makes people say leg curls hurt their knees. Nine times out of ten the pivot is in the wrong place.
• Pointing your toes. Hands your calves the job and invites cramp.
• Only training half the rep. Cutting the range short at both ends is common. Curl until your hamstrings are fully shortened, and lower until they are properly lengthened.

The best leg curl alternatives at home

You do not need a machine. All of these train knee flexion, which is the point.

Nordic hamstring curl. The strongest option and the best studied. Kneel on something soft, anchor your ankles under a sofa or a loaded barbell, and lower your torso towards the floor as slowly as you can while keeping your hips straight, catching yourself with your hands. It is brutally hard, so start by only controlling the top third of the range and use your arms to push back up. Even at shallow knee angles the biceps femoris is working hard (biceps femoris activation during the Nordic hamstring exercise), so partial reps are still worth doing while you build up.

Sliding leg curl. Lie on your back, heels on a towel (hard floor) or furniture sliders (carpet), and lift your hips into a bridge. Slowly slide your heels away from you, keeping your hips up, then curl them back in. Doing it one leg at a time makes it far harder.

Band leg curl. Anchor a resistance band low, loop it around your ankle, lie face down and curl against it. The resistance is lightest where the hamstrings are strongest, which is not ideal, but it is a genuine curl and it costs almost nothing. A decent set of resistance bands covers this and a lot more.

Stability ball curl. Lie on your back with your heels on a exercise ball, bridge your hips up, and roll the ball towards you by bending your knees. The wobble adds a stability demand the machine version does not have.

Where it fits in a leg session

Leg curls are an accessory exercise, so put them after your main lifts, not before. A sensible lower body session might run squats or leg press first, then Romanian deadlifts for the hip-hinge side of the hamstrings, then three or four sets of leg curls for the knee-bending side, and finish with calf raises. Two of those sessions a week is plenty for most people.

If you train at home and want to load these properly over time, a set of adjustable dumbbells plus something to anchor your feet covers nearly everything above.

Recommended reads

• Romanian Deadlift
• Hamstring Exercises
• Leg Extension
• Best Resistance Bands UK
• Workout & Exercise Guides