Lower body · Quads

Leg extension

How to do the leg extension machine: back pad and roller setup, range of motion, common mistakes and how to adapt it if your knee bothers you.

Technique video

The leg extension is an isolation exercise: sitting on the machine, you straighten your knees by lifting a padded roller with your lower legs. It is the most direct way to train the quads and one of the few leg options that does not load the ankle or hip, which is why it appears in many rehab and low-impact routines.

Muscles worked

It trains only the quadriceps, especially the rectus femoris, which works harder here than in the squat.

How to do it

1. Adjust the back pad so your knee lines up with the machine's pivot point (often marked with a colored dot).
2. Place the roller on your lower shins, just above the ankles.
3. Hold the seat handles and keep your back flat against the pad.
4. Straighten your knees until they are almost fully extended and squeeze your quads for a second at the top.
5. Lower slowly over two or three seconds, without letting the weight stack crash.

Common mistakes

• Knee not aligned with the pivot: it creates unnecessary stress on the joint.
• Kicking the weight up and letting it drop.
• Lifting your hips off the seat to move more weight.
• Heavy weight through the full range if your knee is sensitive.

Variations and progression

The single-leg version evens out differences between sides. It works well with sets of 12 to 20 reps and a controlled lowering phase. As a finisher on leg day, it lets you exhaust the quads without loading your back.

Precautions

It only loads the knee. If it bothers you, work in a partial range (for example, from 90° to 30° of knee bend) with moderate weight. It is a good quad option when squats and lunges are off the table because of your ankle or back.

If you have an injury, pain or a medical condition, check with a professional before doing this exercise.