What Happens To Your Knees When You Do Leg Extensions

The leg extension machine is one of the most popular machines in the gym. This device is used to isolate the quadriceps and help you build muscle there (via Livestrong). However, this machine can cause issues for people who have weak knees or injuries with their ACLs or ligaments. The leg extension machine puts a lot of stress on the entire knee area and can easily cause pain and discomfort. It can also increase your risk of developing lateral patellar deviation, which is an injury that involves the kneecap sliding around unnaturally. Because your hamstrings are not engaged while using this machine, your knees receive less support during each movement and are more likely to get hurt.

"The leg extension machine applies constant tension to the anterior cruciate ligament (ACL)...," Chris Ryan, CSCS, told BestLife. "It also places maximum force on the back of the knee cap, which is the thinnest portion of the cartilage." If you want to work your quads, you should try to find safer alternatives to the leg extension machine if possible.

If you want to build your quads, you don't have to risk your knees on the leg extension machine. A simple squat is a great way to work your quadriceps without damaging other parts of your body (via Healthline). To correctly perform a squat, start with your feet hip-width apart and your shoulders back. Keeping your core tight and your back straight, slowly lower your body until your thighs are parallel to the floor. To keep your knees safe, make sure that they don't collapse inward or outward while you squat. After your thighs are parallel to the floor, slowly return to start position. You can hold dumbbells or a barbell if you want to increase your leg strength even more.

Lunges are also great exercises to work your quads. Regular and reverse lunges can build your quad muscles without hurting your knees. They can also be performed with or without added weight.