Why You Should Avoid the Leg Extension Machine like the Plague!


Let’s pump the breaks gym bro. While leg extension is a highly popular exercise in the gym world, it is not all what it’s cracked up to be. Over the past five years of working in physical therapy, the one bit of advice all of the PTs would give to their knee patients was to stay away from any leg extension machine. And here’s why.

When performing a leg extension on a machine, there is a substantial amount of tension that is applied to the anterior cruciate ligament (ACL) and when lifting heavy loads, it can put the user at a higher risk of injury. To dive deeper on why risk of a knee injury is elevated, we must look at the mechanical impact on the joint itself. In a standard leg extension machine, there is a seat with an adjustable back and pad that is placed on the front of the ankle. To perform the movement, the user contracts the quadriceps and extends the knees until they are straight. The movement is completed when the user controls the leg back down to the starting position.

Seems simple right? Lets jump back to the position when the user’s knee is at full extension. At this position, the pad on the ankle is creating a downward force and results in a shift of the tibia (lower leg shin bone) from the femur (thigh bone). This then creates an unstable joint and in return puts immense tension on the ligaments inside the knee. Now we both know that you do not want that.

“But if knee extension machines are bad for me, how do I strengthen my quads?” I’m glad you asked. There are more efficient and more importantly much safer movements for your knee that will strengthen your quads. Movements such as weighted step ups, leg press, squats, and eccentric lowering exercises can help you achieve your goals of shredded quads and stable knees.

Check out my instagram page at @chriskadingCPT for videos on how to keep those knees safe and strong.

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