Leg extensions are isolation exercises that target your quadriceps, generally performed with the aid of a leg extension machine. This machine requires you to lift your lower legs by extending your knees against weighted resistance from a seated position. Leg extension machines are very common in gyms, but if you don't have access to one, you can perform leg extensions using other, less expensive equipment or even just your own body weight.

Leg Extensions

The leg extension exercise works out just one major muscle group, your quadriceps, or "quads." Your quads run along the front of your thigh from your knee to your pelvis and are responsible for hip flexion and knee extension. When you perform leg extensions, you contract the quad to bring your knees up against the weighted resistance. While many other exercises such as squats, lunges or deadlifts also provide a heavy workout for the quads, they do not isolate the muscle like a leg extension does. Any exercise that requires you to contract your quadriceps against resistance can accomplish the same effect as a leg extension machine.

Resistance Bands

Resistance bands are elastic bands that can be used in a variety of exercises. To simulate leg extensions, simply fasten one end of the resistance band around your ankle and the other end around a stationary object such as a bench or chair. Sitting on the chair, extend your lower leg against the resistance of the band. This will force your quadriceps to contract. This extension exercise can also be performed while standing up.

Ankle Weights

Ankle weights are another way to simulate the leg extension. Begin by sitting in a chair with weights around both ankles. Lift both legs up in the air, contracting your quads to work against the added weights on your ankles.

Body Weight

You can simulate the leg extension exercise using nothing more than your own body weight by walking backward on a treadmill or doing a reverse step up onto a slightly raised platform. Both exercises require you to contract and release your quad to complete the range of motion, using the weight of your body rather than a set of weighted plates.