Leg extension vs leg curl: quads or hamstrings?

On leg day, most lifters include leg extensions and leg curls into their strength training routine. Leg extensions and leg curls are often built into strength training routines together as part of a superset during resistance exercise. However, if you separate quad and hamstring work, leg extension vs leg curl is more about which muscle group are you working today.

Is it quad day or hamstring day? Whether you decide on leg extensions or leg curls, both isolate leg muscles to build muscle and strength.

Leg extensions and working your quads

Leg extensions are an isolation exercise that primarily works the muscles in the front of your legs known as the quadriceps. It also helps strengthen the ligaments and tendons around your knee cap.

The quadriceps are used for any sort of knee extension movement such as kicking.

Muscles worked

Leg extensions primarily work the quadriceps muscles, which are found at the front of your thigh.

There are four muscles in this group, including the:

1. Rectus femoris (the main bulk of the muscle)
2. Vastus medialis (the inner part of the thigh)
3. Vastus lateralis (the outer part of the thigh)
4. Vastus intermedius (in the middle behind the rectus femoris). 

If you’re looking to increase size in your quads leg extensions are your go-to exercise.

However, there are various exercises that work quadricep muscles like lunges, squats and deadlifts. But none of these isolate the muscle group as well as leg extensions.

Benefits of leg extensions

Strengthen quads. Leg extensions will help you strengthen your quads more than almost any other exercise. The leg extension is primarily a quad-dominant movement that can work the quads with greater intensity than even the squat.

Beginner and advance friendly. You can use a leg extension machine regardless if you are new to strength training or have been lifting for a while.

How to perform

The leg extension machine uses a padded bar at the top of your lower legs at the ankles to add weight resistance to the movement.

1. Begin in the seated position on the leg extension machine with your knees at a 90-degree angle and your feet anchored beneath the leg rollers. 
2. Grip the handles, tighten your midsection and press your lower back into the seat. 
3. Lift your legs until they reach near extension. Ensure you’re moving through a safe range of motion by not locking your knees.
4. Keep your back against the backrest and do not arch your back.
5. Pause briefly, then slowly lower your legs to the starting position. 

For a home workout, use a chair with a resistance band or ankle weights.

Alternatives leg extension exercise

Use a slant board

A slant board will help emphasize loading the quads while protecting the knees is with a slant board. A slant board is an angled board that is used to elevate the ankles during a squat, similar to a raised heel on a weightlifting shoe.

Dumbbell leg extension

This one requires a chair or weight bench and a dumbbell. You’ll lean back and place the dumbbell between your feet to work your quads. You’ll have to reduce the amount of weight than with the machine.

Cable leg extensions

Doing this exercise requires the use of a weight bench, so it might not be the most convenient exercise if your gym is busy or has limited equipment.

Short stride lunges

Lunges can be modified to make them more quad-centric. Shorten your step to increase the range of motion of your front knee and increasing quads activation. You can add weight by holding dumbbells or kettlebells.

Sissy squats

It involves locking your feet in a fixed position and leaning right back, with the tension on your thighs, before bringing yourself up again on a Sissy Squat Bench. You also can use the Smith Machine by lowering the bar or adjusting the roller of the leg extension machine.

Leg curls and working hamstrings

Leg curls primarily work the muscles in the back of your leg known as the hamstrings. Just like the leg extension, leg curls isolate the hamstrings.

Strong hamstrings are used to bend your knee. They’re used in movements such as running, walking and jumping. They also help in acceleration which makes these muscles important for sports including soccer, football and volleyball.

Muscles worked

Leg curls also known as hamstring curls primarily work the hamstrings, which as found at the back of the legs.

There are three muscles in this group, including the:

1. Semimembranosus (closest to the middle of your body. It flexes your knee joint, extends your thigh at your hip and offers medial rotation for your hip and lower leg.)
2. Semitendinosus (lies medially to the biceps femoris, and covers the majority of the semimembranosus.)
3. Biceps femoris (closest to the outside of your body. It flexes your knee, extends the thigh at your hip and rotates your lower leg from side-to-side when your knee is bent.)

Leg curls should be a part of your strength training routine if you’re looking to increase overall strength of your hamstrings, leg curls should be a part of your strength training routine.

Benefits of leg curls

Leg curls are a great way to target your hamstrings, particularly your biceps femoris. 

Helps with day-to-day movements. When you get up from a chair or get down on the floor, you’re using your hamstrings to help stabilize your hip and knee joints. Adding some hamstring-focused exercises can help make these daily motions easier.

Relieves knee pain. Strengthening your hamstrings helps build stability in your knee and pelvis. This helps improve your knee alignment (and reduces your injury risk).

Disadvantages of leg curls

Lower back pain. If you overload the weight or do not use proper form, you can overwork your lower back. 

How to perform

This is a posterior chain muscle that sits on the back of the leg.

1. Sit on the leg curl machine with your knees slightly bent and your feet resting on top of the rollers. 
2. Grip the handles, tighten your midsection, and press your lower back into the seat. 
3. Push down on the bar until your legs reach a below 90-degree angle. Pushing past the 90-degree angle is an optimal range of motion for the leg curl. 
4. Pause briefly, then slowly raise your legs to the starting position. 

At home, you can do exercises like the nordic curl, good mornings and deadlifts to hit your hamstring muscles.

Leg curl variations

Lying leg curl

A popular variation where you lie on a hamstring curl machine that has you place the pad behind your achilles.

Seated leg curl

Seated leg curls involve sitting against a padded seat with your feet over a padded bar. 

Standing leg curl

Resembles lying leg curls, but hits the hamstrings differently than the seated version.

Wrap up

You can use machines, resistance bands or free weights to work your quads or hamstrings, Both exercises are great for working your lower body. The main difference is that one works the front of your leg and the other works the back of your leg.