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Legs · Leg extension machine

Leg extension: form, muscles and sets

The leg extension is the only common movement that loads the rectus femoris hard with the hip straight — which is exactly what squats cannot do.

Muscles worked: Rectus femoris, Vastus lateralis, Vastus medialis

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How to do it

  1. Set the back pad so the knee joint lines up with the machine's pivot.
  2. Position the shin pad just above the ankle, not on the foot.
  3. Hold the handles, press the lower back into the pad and brace.
  4. Extend until the legs are straight, squeezing the quads for a full second.
  5. Lower over three seconds and stop just before the weight touches down.

Mistakes to avoid

  • Pivot misaligned with the knee, which puts shear through the joint.
  • Swinging the torso to fling the pad up.
  • Dropping the weight fast and losing the whole lowering phase.

Sets and reps

GoalPrescription
Size3–4 sets of 12–20 reps, 60s rest
Knee health3 sets of 15 light with a slow lower and pause
Pre-fatigue2 sets of 15 before squats on a quad-focused day

Swaps and alternatives

  • Sissy squat — Same straight-hip quad load without a machine.
  • Bulgarian split squat — Loads the quads with a balance demand.
  • Reverse Nordic curl — Bodyweight stretch for the rectus femoris.

Common questions

What people ask about leg extension

This guide covers leg extension form, how to do leg extensions correctly, leg extension muscles worked, leg extension sets and reps for muscle growth, leg extension machine rectus femoris exercise and the swaps to run when a rack or bench is taken.

Training the same muscles from another angle? Start with the full exercise library or let the free workout plan generator slot leg extension into a four-week block.

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