Leg Extension
Legs
Weight & Reps
Machine
Leg extensions isolate the quadriceps by extending the knee against resistance. Great as a warm-up or finishing exercise to fully exhaust the quads after compound movements.
How to Do Leg Extension
- Adjust the pad to sit on your lower shins, just above your ankles
- Sit back in the seat with your back against the pad and grip the handles
- Extend your knees fully until your legs are straight, squeezing the quads at the top
- Lower with a slow 3-second negative — don't let the weight stack drop
Form Cues
- Adjust the pad to sit on your lower shins, just above your ankles
- Sit back in the seat with your back against the pad and grip the handles
- Extend your knees fully until your legs are straight, squeezing the quads at the top
- Lower with a slow 3-second negative — don't let the weight stack drop
Common Mistakes to Avoid
- Using momentum to swing the weight up instead of a controlled quad contraction
- Setting the back pad too far forward, which lifts your butt off the seat
- Not reaching full knee extension at the top — lock out for peak quad contraction
Muscles Worked
Primary
Quadriceps (Rectus Femoris)
Quadriceps (Vastus Lateralis)
Quadriceps (Vastus Medialis)
Quadriceps (Vastus Intermedius)
Secondary
Tibialis Anterior
Recommended Sets and Reps
Strength
4-5 sets
3-5 reps
3-5 min rest
Hypertrophy
3-4 sets
8-12 reps
60-90s rest
Endurance
2-3 sets
15-20 reps
30-60s rest
Variations and Alternatives
Frequently Asked Questions
What muscles does the leg extension work?
Leg extensions isolate all four heads of the quadriceps: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. It's one of the only exercises that fully isolates the quads.
How much should a beginner leg extension?
Beginners typically start at 30-60 lbs (14-27 kg). Leg extensions are an isolation exercise — use moderate weight with controlled form and focus on the quad squeeze.
Are leg extensions bad for your knees?
Leg extensions are safe when performed with controlled form and appropriate weight. They can actually strengthen the muscles around the knee. Avoid using excessive weight or jerky movements, and stop if you feel knee pain.
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