How to Do the Leg Curl: Muscles Worked, Form & Alternatives

The leg curl is a hamstring exercise, typically performed on a leg curl machine.

It’s unique among hamstring exercises because it trains your hamstrings through a full range of motion while fully stretched, which makes it ideal for building muscle.

In this article, you’ll learn what the leg curl is, its benefits, which muscles it works, how to do it with proper form, the best seated leg curl alternatives, and more.

What Is the Leg Curl?

Seated Leg Curl vs. Lying Leg Curl: Which Is Better?

That’s because sitting upright with your legs straight in front of you places your hamstrings in a fully stretched position, whereas lying down doesn’t. This is noteworthy because research shows that when it comes to building muscle, training a muscle while it’s stretched is superior to training it while it’s relaxed.

And that’s why studies show doing the seated leg curl leads to more muscle growth than doing the lying hamstring curl. Thus, most people will benefit more from the seated leg curl than the lying leg curl, which is why the seated leg curl is the variation we’ll focus on in this article. 

That said, the lying leg curl is still an effective exercise. If you prefer how it feels or it’s the only machine you have access to, it’s a viable alternative.

Leg Curl: Benefits

The hamstrings have two primary functions: knee flexion (bending your knee) and hip extension (moving your torso away from your thighs).

One of the main benefits of the leg curl is it trains knee flexion, something most other hamstring exercises (all forms of the deadlift, the hip thrust, and the glute bridge, for example) neglect.

Furthermore, the seated leg curl trains knee flexion while the three largest “parts” of the hamstrings—the long head of the biceps femoris, semitendinosus, and semimembranosus—are fully lengthened. This makes it particularly effective for developing the areas of the hamstrings that have the biggest impact on upper-leg size.

Another benefit of the leg curl is that it allows you to train your hamstrings when your back is tired.

This is important because during most exercises that train the hamstrings, such as the deadlift, Romanian deadlift, and squat, your back muscles have to work hard to keep your upper body in a stable and safe position. 

If your lower-body workouts only consist of free-weight exercises like these, your back muscles (and particularly your lower-back muscles) may fatigue faster than your hamstrings. While your back may be bushed after 6 sets of these exercises, your hamstrings may be able to handle a few more.

The leg curl is a helpful workaround in this scenario. It allows you to train your hamstrings after your back is fried, ensuring you can train your hammies with the volume they need to grow and become stronger without your lower back becoming a limiting factor.

For these reasons, I always include the leg curl in my own training and my fitness programs for men and women, Bigger Leaner Stronger and Thinner Leaner Stronger. 

And if you’d like more specific advice about what exercises to include in your training program to reach your health and fitness goals, take the Legion Strength Training Quiz, and in less than a minute, you’ll know the perfect strength training program for you. Click here to check it out.

Seated Leg Curl: Muscles Worked

The leg curl primarily trains the hamstrings, though it also trains the glutes and calves to a small degree, too.

Here’s how the main muscles worked by the leg curl look on your body:

Seated Leg Curl: Form

Step 1: Set Up

Step 2: Curl

Step 3: Extend

The Best Seated Leg Curl Alternatives

1. Lying Leg Curl

2. Nordic Leg Curl

Research shows that the Nordic leg curl is a fantastic bodyweight exercise for training your hamstrings, which may also reduce your risk of suffering a hamstring injury. While it isn’t exactly the same as the seated leg curl, you can use it as an alternative to the seated leg curl at home.

3. Dumbbell Leg Curl

The dumbbell leg curl is similar to the lying leg curl, except you grasp a dumbbell between your feet instead of using a leg curl machine. The dumbbell leg curl can be a useful seated leg curl alternative in a bind, but most people find it awkward to set up and perform. Thus, it’s not a variation I’d recommend unless you don’t have access to a leg curl machine (while working out at home or traveling, for example).

4. Swiss Ball Leg Curl