Leg Extensions

How to Do Leg Extensions

Proper Form, Variations, and Common Mistakes

machine leg extension

Targets: Quadriceps

Equipment Needed: Leg extension machine

Level: Beginner

Leg extensions are exercises usually done with a lever machine. You sit on a padded seat and raise a padded bar with your legs. The exercise works mainly the quadriceps muscles of the front of the thigh—the rectus femoris and the vastus muscles. You can use this exercise to build lower body strength and muscle definition as part of a strength training workout.


The leg extension targets the quadriceps, which are the large muscles of the front of the thigh. Technically, this is an "open chain kinetic" exercise, which is different from a "closed chain kinetic exercise," such as a squat.1 The difference is that in the squat, the body part you're exercising is anchored (feet on the ground), while in the leg extension, you're moving the padded bar, which means your legs aren't stationary as they work, and thus the chain of movement is open in the leg extension.

The quads are well-developed in cycling, but if your cardio is running or walking you are mostly exercising the hamstrings at the back of the thigh. In this case, you may want to develop the quads to be more in balance. Building your quads can also increase the force of kicking movements, which can be beneficial in sports such as soccer or martial arts.

Step-by-Step Instructions

Set up the leg extension machine so the pad is at the top of your lower legs at the ankles. Your knees are at 90 degrees. Select a weight that will give you a moderate load for 10 to 12 repetitions.

  1. Place your hands on the hand bars.
  2. Lift the weight while exhaling until your legs are almost straight. Do not lock your knees. Keep your back against the backrest and do not arch your back.
  3. Exhale and lower the weight back to starting position.
  4. Do three sets of eight to 12 repetitions.

Common Mistakes

Avoid these errors so you will get the most benefit and prevent strain or injury.

Heavy Lifting

This is not the machine to try for a maximum lift (1RM), which is the most weight you can lift for just one rep. Due to the risk of knee ligament strain, do not use this exercise for low-rep, high-load strength conditioning.

High Reps

Don't do more than three sets of eight to 12 reps at moderate load. You don't need to do any endurance sets with high repetitions on the leg extension machine.

Going Too Fast

Doing this exercise with any speed will use momentum rather than muscle engagement.

Locking the Knees

Do not lock your knees at full extension. This can strain the knee joint.2

Modifications and Variations

This exercise can be done in different ways to work your quads.

Need a Modification?

Rather than using a leg extension machine, you can do leg extensions using ankle weights or resistance bands.

For a seated leg extension with ankle weights, start with 5-pound weights and progress only to 10-pound weights. Or, loop a resistance band around your ankle and around the rear leg of the chair on the same side.

  1. Sit in a chair with your back straight.
  2. Lift one leg to straight out from your body.
  3. Hold for five seconds.
  4. Lower to starting position.
  5. Repeat with the other leg.

For a standing leg extension using a resistance band, you would anchor on end of the band behind you and loop the band around your ankle. Stand in a position where the band has no tension when your knee is bent with ankle behind you. Hold a rail or chair for balance as needed.

  1. Slowly straighten your knee to bring to the band under tension, maintaining a straight back.
  2. Extend as far as comfortable. Pause and slowly return to the starting position.
  3. Perform 10 repetitions, then do the same with the other leg.

Up for a Challenge?

Gradually increase the weight as you gain strength, but keep the load moderate. You can do one-leg leg extensions to work on each leg individually.

Mix up your quadriceps workout. Make sure you also do squats for lower body conditioning.

Safety and Precautions

If you have a knee, ankle, or thigh injury, seek guidance from your doctor, a qualified physical therapist, or strength and conditioning coach who specializes in weight training rehabilitation. They may say to avoid the leg extension machine. Critics say that open chain exercises like the leg extension can damage the knees and that even full-depth squatting is safer.2 Stop this exercise if you experience any pain in your knee or ankle. Be sure to follow proper form when doing leg extensions and mix up your quadriceps workout.

Try It Out

Incorporate this move and similar ones into one of these popular workouts: