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Exercise library · Quads

Single leg extension

Knee extension for the quads on a machine.

How to do it

1 of 3

One ankle behind the roller

  1. Starting position

    Sit with your back against the pad, one ankle behind the roller and your knee in line with the machine pivot.

  2. The movement

    Extend the working leg until the knee is nearly straight, then lower it back with control.

Most common mistake

Don't swing the roller up, keep your hips on the seat and lift with the front of your thigh.

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Muscle group
Quads
Equipment
Machine
Where
Gym
Logged as
Weight × reps

Muscles worked

Here your quads work one leg at a time, with your hips still and no help from your glutes or hamstrings. The muscles are the same as in the two-legged leg extension, but each thigh works on its own, so you see straight away whether both sides manage the same weight and reps. That makes it a useful tool if one thigh is visibly smaller or weaker, as you can give that side an extra set. The machine handles balance, so the only limit is the thigh itself.

Common mistakes

  • The resting leg helps out. On a machine with a wide roller, the other leg can easily push too. Tuck the free foot back under the seat so it cannot reach the roller.
  • The roller drops back down. The lowering is half the exercise, yet many people just let the weight fall. Follow it down over two to three seconds and let the stack stop just before it touches.
  • Your foot turns to the side. As the weight gets heavy, your foot tends to rotate and your knee goes with it. Keep your toes pointing straight up throughout the rep.

Variations and alternatives

  • The leg extension with both legs saves time when your sides are evenly matched.
  • The single leg press also trains one leg at a time, but brings in your glutes and handles heavier loads.
  • The Bulgarian split squat is a free-weight option on one leg when the machine is taken.

Sets and reps

A good plan is 2 to 3 sets of 10 to 15 reps per leg. Let your weaker leg choose the weight, then give the stronger one the same weight and the same reps. If one side needs to catch up, it can get an extra set. Put the exercise last in your leg session, once the heavy compound lifts are done. You will find more example set-ups in the guide to sets and reps.

A step on the weight stack that feels small with two legs can be a big jump for one. So stay at the same weight until you manage 15 reps in every set, and only then go up. Progressive overload on one leg in a machine is more about reps than kilos.

Swap for

Taken, or missing the equipment? The same movement with something else.

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