Muscles worked
What the leg extension trains
Tap a muscle to see just that one and what it does in the lift.
Before the first rep
How to set up
- 01
Set the back pad. Move the backrest so your knees sit just past the front edge of the seat and line up with the machine's pivot point, usually marked with a dot or arrow on the side.
- 02
Set the shin pad. Adjust the roller so it rests on the front of your lower shins, just above the ankles, not on your feet or halfway up your shins.
- 03
Choose the start angle. If the machine has a range setting, start where your knees feel comfortable bent, roughly at a right angle or a little deeper.
- 04
Sit tall and hold on. Sit all the way back against the pad, grip the side handles, and keep your feet relaxed and pointing up.
Step by step
How to do the leg extension
- 01
Brace. Pull yourself into the seat with the handles and take a breath so your hips stay down for the whole set.
- 02
Extend. Straighten your knees in a smooth motion, lifting the pad until your legs are straight or close to it. Keep it steady, with no kicking or swinging to get the weight moving.
- 03
Squeeze. Pause for about a second at the top and tighten the front of your thighs. Do not snap your knees back hard into lockout.
- 04
Lower slowly. Take two to three seconds to lower the pad back to the start angle, keeping tension on your quads instead of letting the weight stack crash.
- 05
Repeat. Start the next rep just before the plates touch, so your quads stay working through the set.
Cues to say in your head
- Knees on the pivot
- Hips glued to the seat
- Lift with your shins
- Squeeze at the top
- Slow on the way down
Fix these first
Common mistakes
Knees not lined up with the pivot
Move the back pad until your knee joint sits beside the machine's axis. Out of line, the pad slides along your shin and the pull on your knee feels awkward.
Hips lifting off the seat
Hold the handles, sit back, and use a weight you can lift without your hips rising. Lifting the hips lets momentum and hip flexors take over.
Swinging or kicking the weight up
Slow the lift down and pause at the top. If you need a kick to finish a rep, the weight is too heavy.
Dropping the weight back down
Lower over two to three seconds. Lowering under control keeps your quads working, and a crashing stack jars the knee.
Pad set too high or on the feet
Put the roller just above your ankles. Higher up the shin shortens your leverage and changes how the load feels on your knee.
Stay safe
The leg extension is easy to fail safely: if you cannot finish a rep, lower the pad slowly to the start and stop the set. Start light, keep the movement controlled, and pick a start angle and range that feel comfortable for your knees. Some people find it bothers their knees and others tolerate it well, so if you feel sharp pain or pain around the kneecap, stop, try a lighter weight or shorter range, and see a physio or doctor if the pain continues or you are coming back from a knee injury.
Programming
Sets, reps and how much weight
| Goal | Sets | Reps | Load | Rest |
|---|---|---|---|---|
| Muscle | 3 to 4 | 10 to 15 | 60–75% 1RM | 1 to 2 min |
| Endurance | 2 to 3 | 15 to 25 | 45–60% 1RM | 45 to 90 sec |
| Technique | 2 to 3 | 12 to 15 | 40–55% 1RM | 1 min |
Plan your next session
Put in a recent set. You get working weights for your goal, a warm-up and the plates to load.
Estimated 1RM 216 lb
Endurance sets
97–129lb
2 to 3 sets of 15 to 25 reps, 45 to 90 sec rest. Lighter, high-rep sets, common as a finisher after your main leg work.
Estimates use the Epley formula and work best from sets of 3 to 8 reps. Treat them as a starting point and adjust by how the first working set moves.
Questions
Leg Extension questions
What muscles do leg extensions work?
Leg extensions work the quadriceps, the four muscles on the front of your thigh, almost entirely on their own. Your grip and core only help keep you in the seat.
What is good leg extension machine form?
Line your knees up with the machine's pivot, set the pad just above your ankles, and keep your hips on the seat. Lift smoothly, pause at the top, and lower over two to three seconds without swinging.
Are leg extensions bad for your knees?
Not for most people, used with a sensible weight and control. Some people with sensitive knees find a shorter range or lighter load more comfortable, and anyone with knee pain or a recent injury should get advice from a physio first.
How many sets and reps of leg extensions should I do?
For quad size, 3 to 4 sets of 10 to 15 reps taken close to failure works for most people. Lighter sets of 15 to 25 suit a finisher at the end of leg day.
Should I lock out my knees at the top?
Straighten your legs fully or close to it and squeeze, but do not snap the knees back hard. A controlled pause at the top keeps tension on the quads.
Where should the pad sit on my legs?
On the front of your lower shins, just above the ankles. Too high up the shin or on top of your feet changes the leverage and usually feels worse.
Train in Protocol
Log your leg extension by voice. Protocol tracks the rest.
Your last session shows up before every set, warm-ups and plates are worked out for you, and your coach sees every lift next to your sleep and recovery.