How to do a leg extension
- Adjust the backrest so the back of your knees sits at the front edge of the seat and your knees line up with the machine’s pivot point.
- Set the shin pad so it rests on the lower part of your shins, just above your ankles.
- Sit back, hold the handles at the sides, and keep your hips down on the seat.
- Straighten your knees to lift the pad until your legs are straight or nearly so.
- Pause briefly at the top, then lower slowly until your knees are bent to about 90 degrees or a little more.
Cues that help
- "Knees on the pivot": the right seat setting makes the movement smooth instead of grinding.
- "Pull yourself into the seat": holding the handles keeps your hips from lifting.
- "Squeeze at the top": a short pause with straight legs.
- "Two seconds down": control the weight back to the start.
Common mistakes
- The seat in the wrong place. If your knee is in front of or behind the pivot, the movement feels awkward and loads the knee oddly.
- Swinging the weight up with a kick. Lift it with your quads, not momentum.
- Hips lifting off the seat. Hold the handles and use a weight you can lift without it.
- Dropping the weight. Lowering slowly is half the exercise.
- Only doing the top half. The bent-knee part of the range matters (see below).
Which part of the range matters?
One study had 45 untrained women train the leg extension for several weeks in different ranges. The group that trained only the bent-knee half (from 100 to 65 degrees of knee bend) grew some regions of the quads more than the groups training the full range or the straight-knee half (Pedrosa et al., 2022).
It is one study, in beginners, so do not cut your range in half because of it. The practical point: the deep, bent-knee part of the leg extension, where the quads are stretched, is the valuable part. Make sure your reps start from a properly bent knee, not halfway up.
Sets, reps and weight
- For muscle: 2 to 4 sets of 10 to 15 reps, stopping 0 to 2 reps short of failure. The machine makes it safe to go hard.
- Rest 1 to 2 minutes between sets.
- Use it after your main leg exercise, or as the main quad exercise if squats and leg presses do not suit your knees or back.
- Add weight once you reach the top of your rep range on every set.
Is it bad for your knees?
The leg extension puts a load across the knee that squats share with the hips, which is why it has a reputation. For healthy knees, a controlled leg extension with a sensible weight is a normal gym exercise, and it is widely used in knee rehabilitation.
If it hurts at the front of your knee, try a lighter weight, a shorter range near full extension, or one leg at a time, and talk to a physiotherapist if the pain stays.
Variations and alternatives
- Single-leg extension: one leg at a time, to even out a weaker side.
- Reclined leg extension: the backrest leaned back, which stretches the rectus femoris (the quad that crosses the hip) more.
- Sissy squat: a body-weight quad exercise with the knees travelling far forward.
- Leg press or hack squat with feet low: more quads within a compound movement.
- Bulgarian split squat: quads and glutes, one leg at a time.
Tracking your leg extensions
PushBeyond logs the weight and reps of each set and charts the history of the exercise. Its muscle map counts the leg extension for your quads.