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.

Benefits of Leg Extensions

The leg extension targets the quadriceps, the large muscles of the front of the thigh. This “open chain kinetic” exercise differs 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 balanced. Building your quads can also increase the force of kicking movements, benefiting sports such as soccer or martial arts.

How to Do a Leg Extension

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 the starting position.
4. Do three sets of eight to 12 repetitions.