Leg Extension
The leg extension is a machine-based isolation exercise that targets the quadriceps. Extending the knee against resistance from the seated position provides direct stimulation to the quad muscles, commonly used for hypertrophy and rehabilitation.
How to do it
- Sit in a leg extension machine with your back flat against the pad and knees aligned with the machine's pivot point.
- Hook your ankles under the roller pad and grip the handles on the sides.
- Extend your legs upward until they are fully straight, squeezing your quads at the top.
- Slowly lower the weight back to the starting position, stopping just before it touches the stack.
- Repeat for the desired number of repetitions.
Form cues
- Align your knees with the machine pivot point
- Keep your back firmly against the pad
- Extend your legs smoothly without locking your knees
- Lower the weight with control
Breathing: Exhale as you push the weight upward, and inhale as you slowly return to the starting position.
Common mistakes
- Lifting hips off the seat to push more weight, which reduces quad engagement and strains the lower back.
- Using momentum by swinging the legs, which decreases muscle activation and places stress on the knee joints.
- Adjusting the back pad incorrectly, which misaligns the knees and causes discomfort during the movement.
Muscles worked
Primary: quads. Secondary: hip flexors.
Suggested sets & reps
Get fitter
3 sets × 10–12 reps, rest 60 s
Lose weight
3 sets × 12–15 reps, rest 45–60 s
Build muscle
3–4 sets × 8–12 reps, rest 90 s
Easier, harder & alternatives
Make it harder
Alternatives
Take care if…
- If you feel sharp or unusual knee discomfort, ease off or choose a gentler leg exercise.
General educational guidance, not medical advice. Stop on sharp pain and check with a qualified professional if unsure.
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Start free →Frequently asked questions
Where should I feel this exercise?
You should feel the work primarily in the front of your thighs, known as the quadriceps.
Should I lock my knees at the top?
Avoid locking your knees aggressively at the top. Straighten your legs fully while keeping a soft, controlled position.
How often can I do leg extensions?
Once or twice a week is plenty for most beginners, allowing at least 48 hours of recovery between leg workouts.