How to Do the Leg Extension Exercise

Work your quadriceps safely

The leg extension exercise is a popular move for targeting the front thigh muscles—the quadriceps— including the rectus femoris and vastus muscles.

The equipment version of the leg extension requires a lever machine with a padded front bar, which you push upward as you extend your legs. 

Some fitness authorities debate the leg extension exercise. Critics argue that, because it traps the knee joint into one movement path, it can lead to injury. Meanwhile, other experts use the exercise in knee/thigh rehabilitation, utilizing light weights and monitored repetitions. If you are concerned about leg extensions as an exercise, there are alternative exercises. For instance, you can perform the lunge instead, including the front lunge.


Leg Extension Exercise: Setup and Movement

The starting position.
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  1. Sit on the padded seat of the machine.
  2. Hook the feet under the padded bar. Adjust the bar so that it rests comfortably at the lower end of the leg, above the feet.
  3. Adjust the machine so that your legs can bend at a 90-degree angle. Don't perform the exercise with less than a 90-degree angle, because this places the knees beyond the toes, which stresses the knee and can result in injury.
    Note: If the machine in your gym does not have leg length adjustment, don't use it; a poorly adjusted position can apply force to improper places in the legs and knees, which can lead to injury.
  4. Choose a weight that enables you to extend the legs straight with effort but not too much strain. Initially, select a light weight from the stack. Do not use this exercise to test your maximum leg strength, as this stresses the knee and can cause injury.
  5. Grip the bars firmly at your sides. Hold your head steady. Brace, and breathe out on exertion and in on recovery.
  6. Extend your legs, engaging your quadriceps to lift the weighted bar. Pause at the top of the extension.
  7. Slowly lower the weight back to the starting position.
  8. Repeat the exercise, doing two to three sets of eight to 12 repetitions each.

Leg Extensions: Points to Note

A leg extension.
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  1. Make sure your back is pushed back firmly against the backrest, particularly at the base of the spine.
  2. Keep the head and neck still while performing the leg extension. Don't wobble forward, back or to the sides. Use the hand grips to keep your body stable.
  3. Don't use very heavy weights for this exercise. Keep the load light to moderate, to help alleviate pressure on your knees through the extension.
  4. Adjust the leg bar length appropriately so that the padded bar is not too far up the shins. As mentioned, the pad should rest against the lower leg, just above the feet.
  5. Don't perform this exercise if it causes pain in your knees as you go. 
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