How to Do a Leg Extension: Proper Form, Variations, and Common Mistakes

Verywell / Ben Goldstein

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.

How to Do a Leg Extension

Verywell / Ben Goldstein

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.

Benefits of Leg Extensions

The leg extension targets the quadriceps, the large muscles of the front of the thigh. This is an "open chain kinetic" exercise, which is different from a "closed chain kinetic exercise," such as a squat.

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 mainly exercise 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.

Other Variations of Leg Extensions

You can perform this exercise in different ways to meet your skill level and goals.

Leg Extension with Ankle Weights

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.

Standing Resistance Band Leg Extension

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.

You can also perform a standing leg extension using a cable machine. You will need an ankle cuff to perform it this way. Make sure you fully extend your leg and use light enough weight to contract your quad at the top of the movement.

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.

Going Too Fast

Doing this exercise with any speed will use momentum rather than muscle engagement. Using momentum will detract from your results and eliminate the effect of isolation exercise since you are recruiting other muscles to help you complete the lift instead of placing the tension on the quads where it belongs.

Locking the Knees

Do not lock your knees at full extension if you are concerned about knee pain or strain, as this can strain the knee joint. Ensure you fully contract your quads at the top, but you can keep a slight bend in your knees to avoid straining them.

Safety and Precautions

If you have a knee, ankle, or thigh injury, seek guidance from your doctor, a qualified physical therapist, or a strength and conditioning coach specializing in weight training rehabilitation. They may say to avoid the leg extension machine.

Critics say that open chain exercises like leg extensions can damage the knees and that full-depth squatting is safer. However, the leg extension machine is an excellent way to add volume to your quad training without the systemic and other muscular fatigue that comes with squatting and other compound movements.

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.

Frequently Asked Questions

  • Is leg extension better than squats?

    Leg extension is not better than squats per say. Squats are an essential compound lift that will activate more muscles in your body than just the quads. Leg extensions are a isolation exercise for the quads and are excellent for adding volume to quad training without additional fatigue that comes from more squatting. Add both to your programming for best results.

  • What is the best leg exercise?

    The best leg exercises are squat variations, according to most experts. These include back squats, front squats, split squats, goblet squats, and more. However, that does not mean it is the only leg exercise you should do. A variety of leg exercises including unilateral and bilateral movements will ensure you hit all of the muscle groups and planes of motion that can build strength, muscle, and functionality.

  • Do leg extensions slim thighs?

    Leg extensions do not slim thighs. No exercise designed to strengthen or build muscle will slim or cause fat loss on any body part directly. Instead, building muscle in your legs will create a curved, firm shape that can be revealed if bodyfat levels are also reduced through a calorie deficit. Spot training or spot reduction is a mostly a myth.

Try It Out

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

5 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Bączkowicz D, Kręcisz K, Borysiuk Z. Analysis of patellofemoral arthrokinematic motion quality in open and closed kinetic chains using vibroarthrography. BMC Musculoskelet Disord. 2019;20(1):48. doi:10.1186/s12891-019-2429-z

  2. Tumminello, N., Vigotsky, A. Are the seated leg extension, leg curl, and adduction machine exercises non-functional or risky?. Personal Training Quarterly. National Strength and Conditioning Association; 2017: (4): 4.

  3. Paoli A, Gentil P, Moro T, Marcolin G, Bianco A. Resistance training with single vs. Multi-joint exercises at equal total load volume: effects on body composition, cardiorespiratory fitness, and muscle strength. Front Physiol. 2017;8:1105. doi:10.3389%2Ffphys.2017.01105

  4. Appleby BB, Cormack SJ, Newton RU. Unilateral and bilateral lower-body resistance training does not transfer equally to sprint and change of direction performance. Journal of Strength and Conditioning Research. 2020;34(1):54-64. doi:10.1519/JSC.0000000000003035

  5. Howe, Louis & Goodwin, Jon & Blagrove, Richard. (2014). The integration of unilateral strength training for the lower extremity within an athletic performance programme. Strength and Conditioning. 

By Paul Rogers
Paul Rogers is a personal trainer with experience in a wide range of sports, including track, triathlon, marathon, hockey, tennis, and baseball.