Leg Extension Don'ts
Good old leg extensions. They are such a seemingly simple exercise aren't they? But if they are so simple, then why do so many people perform them incorrectly?
There are a lot of ways to mess up the leg extension, but the one that irks me the most is when a person rotates their knees in and out or internal and external.
I understand why folks do it. They are trying to place the load on their inner quad (vastus medialis or VMO) and/or their outer quad (vastus lateralus) to develop those muscles more– also, known as the "tear drop" and the "sweep" for you bodybuilders. No matter what you call it, this technique is a bad idea!
Rarely do I ever call an exercise or technique good or bad as a blanket statement, but this is actually one of the few exercise techniques I HIGHLY recommend against.
It's important to know that structure determines function. Things work based on the way they are built. For example, your car door probably does not open like a Dolorean. It opens like most cars and swings out. This isn't by chance, it's by design. Car manufacturers purposely structure the hinge of the door to make it work this way. At the same time, it's probably not a good idea to let your kids hang on the door. After a while, the hinges would warp, and you would probably have to lift the door to close it.
Your knee is pretty much built like your car door. Its structure will only allow it to bend on one axis. Rotating your knees on the leg extension is exactly like letting your kids swing on your car door. Your knee just isn't built for it, and it will only cause problems in the end.
In case you're wondering, here is the proper way to do a leg extension.