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Exercises

Leg extension: how to set the machine, do it and swap it

Published October 17, 2026

The leg extension is a seated machine exercise where you straighten your knees against a padded lever, so your quads do all the work with your hips out of it. It trains all four quad muscles, including the front-thigh muscle that squats work least. What makes it work is the setup: line your knees up with the machine's pivot, then lower every rep until your knees bend past 90 degrees.

Your last leg extension set

How to do the leg extension

The only common lift that trains your quads with your hips out of it, so you can take them close to failure after squats without your glutes or lower back ending the set.

Steps

  1. Move the backrest until the crease of your knee sits at the front edge of the seat and your knee lines up with the pivot, usually marked with a coloured dot.
  2. Set the shin pad so it rests on the front of your lower shin, a couple of fingers above where your foot bends.
  3. Sit all the way back, hold the side handles and pull your hips down into the seat.
  4. Straighten your legs until your knees are fully extended and hold the top for a second.
  5. Lower the pad slowly until your knees bend past 90 degrees, then start the next rep without letting the stack rest.

Cues

  • Knees at the pivot
  • Hips pinned to the seat
  • Lower slower than you lift

Common mistakes

  • Seat set too deep or too shallow, so the pad slides up and down your shin during the rep: move the backrest until your knee and the pivot line up.
  • Kicking the weight up and letting your hips lift: pull down on the handles and pick a load you can raise without a swing.
  • Stopping halfway down: the bent-knee bottom is where your quads stretch, so lower until the plates almost touch.

Swap for: Single-Leg Leg Extension, Sissy Squat, Hack Squat

Muscles the leg extension works

The leg extension works your quads: the three that only cross the knee and the rectus femoris, which also crosses the hip and gets the least work from squats. It loads them through the whole range, with the hardest point near the top as your knees straighten, so a full squeeze at the top and a slow, deep lowering both count.

Sets, reps and reps in reserve for the leg extension

GoalSets × repsRIRRest
Build muscle 3 × 15–20 2 90 s
This matches what the session builder below prescribes for the leg extension.
After squats or the leg press 2–3 × 12–20 0–1 90 s
Your quads are already worked, so a lighter load taken to the last rep you can finish cleanly is enough.
Heavier quad work 3–4 × 8–12 1–2 2 min
Use it when the leg extension is your main quad lift of the day and add weight once every set reaches 12.
Beginners 2–3 × 12–15 2–3 90 s
Spend the first sessions finding your seat and pad settings, log them, and add a plate each week you reach 15 on every set.

Leg extension variations

  • Single-Leg Leg Extension start position

    Single-Leg Leg Extension

    Pick it when one leg is clearly smaller or weaker, or when the stack is too light for both legs together; train the weaker leg first and match its reps with the other.

    Build a session with it
  • Sissy Squat start position

    Sissy Squat

    Use it when you have no machine: kneeling and leaning back with your body straight bends only your knees, the same job the leg extension does.

    Build a session with it

Leg extension alternatives

Other machines

  • Hack Squat start position

    Hack Squat

    The best gym swap for heavy quad work: your back is supported, so your legs end the set.

    Build a session with it
  • Close-Stance Leg Press start position

    Close-Stance Leg Press

    Set your feet low and close on the platform when the leg extension is taken; it keeps most of the work on your quads.

    Build a session with it

Dumbbells

  • Heels-Elevated Goblet Squat start position

    Heels-Elevated Goblet Squat

    With one dumbbell, raising your heels lets your knees travel further forward, so your quads do more of each rep.

    Build a session with it
  • Bulgarian Split Squat start position

    Bulgarian Split Squat

    Pick it when you want one leg at a time with dumbbells; keep your torso upright to bias your quads.

    Build a session with it

Bands or bodyweight

  • Band Spanish Split Squat start position

    Band Spanish Split Squat

    With a band anchored in front of you, it lets you sit deep into a split squat with your shin staying near vertical.

    Build a session with it
  • Skater Squat start position

    Skater Squat

    With no equipment at all, a slow single-leg squat to a low depth takes your quads close to failure in few reps.

    Build a session with it

How to set up the leg extension machine

Every leg extension has the same three settings: the backrest, the shin pad and sometimes the range limiter. Set the backrest first so your knee lines up with the pivot, then the shin pad so it sits on your lower shin, then the start position so your knees begin bent past 90 degrees.

Write the numbers down. Most machines label each setting, and logging them with the weight means you start every session in the same position and your numbers stay comparable.

Leg extension vs squat

The squat trains your quads, glutes and adductors together and lets you lift far more weight. The leg extension trains only your quads, with no balance and no hip drive, so you can push them closer to failure after your main lift.

Do both if you can: a squat or hack squat first, then two or three sets of leg extensions. If you only have time for one, pick the squat pattern.

Questions

What muscles do leg extensions work?

Leg extensions work your quadriceps, the four muscles on the front of your thigh. They are one of the few lifts that train the rectus femoris, the quad that also crosses your hip, close to failure.

How should you set up the leg extension machine?

Move the backrest until your knee lines up with the machine's pivot, then set the shin pad on your lower shin just above your ankle. Set the start so your knees begin bent past 90 degrees, and log each setting so you can repeat it.

Are leg extensions good for building muscle?

Yes. Taken through a full range and stopped 0 to 2 reps short of failure, they build your quads well, and they add quad work after squats without tiring your lower back or glutes.

What can I do instead of leg extensions?

In the gym, use the hack squat or a close-stance leg press. With dumbbells, use heels-elevated goblet squats or Bulgarian split squats. With no equipment, sissy squats and skater squats work your quads hard when you take them close to failure.

How do you do a leg extension without a machine?

Kneel on a mat and lean back with your body straight from knees to head, then pull yourself upright with your quads: that is a sissy squat. For load, sit on a high bench and straighten one leg against a band looped around your ankle and anchored behind you.

How many sets and reps of leg extensions should I do?

Three sets of 15 to 20 reps, stopping about 2 reps short of failure with 90 seconds of rest, is a good default. Count them toward the 10 to 20 hard sets your quads need each week.

Should you lock your knees at the top of a leg extension?

Straighten your knees fully and hold for a second; the top is where the machine loads your quads hardest. Control it rather than snapping into it, then lower slowly.