Step-by-Step Instructions

1. 1

   Adjust the backrest so your knees align with the machine's pivot axis, and position the ankle pad just above the ankle joint on the lower shin.

2. 2

   Sit with your back firmly against the pad, grip the side handles, and start with your knees bent at approximately 90 degrees.

3. 3

   Extend both knees simultaneously, contracting the quads to bring the shins to a fully horizontal position.

4. 4

   Squeeze the quadriceps hard at full extension for 1-2 seconds, focusing on the contraction around the kneecap.

5. 5

   Lower the weight under control through a 3-second eccentric, stopping just before the weight stack touches down.

6. 6

   Avoid using momentum or jerking the weight up from the bottom—initiate each rep with a deliberate quad contraction.

Common Mistakes

• Setting the ankle pad too high on the shin, which reduces the lever arm and decreases quadriceps loading.

• Lifting the hips off the seat during the extension, using body momentum to cheat the weight up.

• Allowing the knees to drift forward of the pivot point by sitting too far back, which increases shear forces on the knee joint.

• Kicking the weight explosively and letting it free-fall on the eccentric, losing half the hypertrophy stimulus.

About This Exercise

The machine leg extension is an open-chain isolation exercise that targets all four heads of the quadriceps—rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius—through pure knee extension. Because the hip angle is fixed in a seated position, the rectus femoris is placed in a shortened position and the vasti muscles bear the primary load. This exercise is invaluable for quad hypertrophy, VMO development for knee health, and as a pre-exhaust or finisher in leg training.