How to: LEG EXTENSION (video)

In this tutorial, we will go over the target muscle, setup, form, and more for the leg extension. For more workout tips, tricks, and information, follow me on Instagram @daniellehamlin or visit the Exercise Library​ :) Enjoy the video!


Single Joint Movement

Joint and Joint Type Involved: Knee, hinge joint.

Main Muscles Worked: Vastus Lateralis, Vastus Intermedius, Vastus Medialis, Rectus Femoris

Equipment: Machine Prerequisites: Ability to contract quads and produce knee extension against the weight of limb without pain or problems.

A leg extension is a single joint movement that focuses on the contraction of the quadriceps to produce knee extension against the weight of the machine. Before you attempt to do this exercise be sure you can adequately contract your quads to extend the knee without any pain. Once you have demonstrated that you can sufficiently contract your quads without any problems you may be ready to contract your quads against additional weight. For this exercise, you will need to use a leg extension machine.


1. Setup the machine. Adjustments may need to be made to get the pad in a comfortable position on your shins. You may also need to increase or decrease the starting angle of the shin pad depending on the range of motion that is available to you in your knees. Adjust the back pad so that your knees line up with the pivot axis of the machine.

2. Pick a weight. It would be beneficial to pick a light weight at first to assess your range of motion and your ability to CONTROL the weight. DO NOT whip the weight around… ever. Once you have demonstrated control you may be ready to increase the weight.

3. Setup your body. Ensure that your ankles, knees, and hip joints are all aligned. The knee is a hinge joint, meaning that it only works in one plane of motion (think door hinge). If your knees and feet are too wide then you are attempting to contract your quads against a force angle that is not favorable to biomechanics or knee health and longevity.

4. Stabilize. Before you do a rep be sure to stabilize everything as much as possible that is not the knee joint. This will ensure that you are producing as much output in the quads as you can.

Areas to stabilize:

-Grab the handles on the side of the machine and pull your butt further into the chair pad.

-Sit up tall, pack the shoulder blades, and engage your abs to keep your upper body from swinging around.

5. First rep. To initiate knee extension contract the quads and continue to focus on the contraction through the rep.

6. Establish control and ranges. Pause at the top of the rep to establish control and determine the end of your range where you still have tension on the quad and do not experience any pain or joint discomfort. Slowly bring down the weight, again focusing on the quads. Only go as low as you can go without losing tension on the quads.

NOTE: If the pad bounces at the top then you are not controlling the weight and you are using momentum, not your quads, to move the weight.

7. Repeat steps 3-6 until your set is complete.

For common mistakes and easy corrections, see 2:43​ 👍