Is the leg extension bad for your knees?

When performed with controlled tempo and appropriate weight, it is a safe way to isolate the quads. Avoid using excessive ego-driven weights that force you to jerk the movement, as this can increase shear force on the ACL.

Should I point my toes up or down?

Keeping your toes pointed upward (dorsiflexion) generally helps maintain tension in the quadriceps and prevents the calf muscles from taking over the movement.

Where should the pivot point be?

The circular hinge of the machine should be exactly aligned with the side of your knee joint to ensure a natural range of motion.

Leg Extension Guide: Master the Quadriceps Isolation

Learn the correct form for the leg extension machine. Build stronger quads and improve knee stability with our professional strength coach guide.

How to Perform

Sit on the machine with your back flat against the backrest and adjust the seat so your knees align with the machine's pivot point.
Position the padded lever so it rests just above your ankles on the lower part of your shins.
Grasp the handles on the sides of the seat to stabilize your upper body and pull yourself firmly into the pad.
Exhale as you extend your legs upward until they are fully straight but not locked out at the knee.
Squeeze your quadriceps at the top of the movement for one second to maximize muscle engagement.
Lower the weight slowly under control until your knees are back at a 90-degree angle.
Maintain constant tension on the muscles by stopping just before the weight plates touch the stack.

Common Mistakes

Using momentum or swinging the weight instead of using controlled muscle contractions
Allowing the lower back to arch or lift away from the backrest during the lift
Setting the ankle pad too high on the shins or too low against the feet
Locking the knees aggressively at the top of the repetition

Muscles Worked

Primary movers

Quads

Stabilizers

Rectus femoris
Vastus lateralis
Vastus medialis

Related Guides

Quads · Legs