So your knees hurt, huh? I bet your one of the nads who thinks your knees hurt because you were doing squats (and probably doing them wrong). So what did you do? Stop doing squats, I bet, and start doing extensions figuring that would be better for your knees. Guess what? You figured wrong.
Think of your leg as two sticks end-to-end. Rubber bands on either side of the sticks keep the ends aligned. But what happens if one of the rubber bands is tighter than the other? The ends of the sticks can slip and are no longer aligned. This is the same thing that can happen knee when you start working muscles in isolation with exercises like the leg extension or leg curl.
The knee joint is stabilized by the big muscles of the upper leg, mainly the quads and the hamstrings, and to a lesser extent the groin (adductors) and hip abductors. All of these muscles work together to keep your thigh bone and tibia aligned.
When you exercise the leg with big lift compound exercises like squats or dead lifts or power cleans, all these muscles maintain tension. This tension keeps your knee joint aligned and minimizes stress on the joint.
Isolation exercise like leg extensions and leg curls force a motion that is not typically naturally occurring. When you work these muscles in isolation, you bypass the body’s natural mechanics. When you do that, you put yourself at risk of injury and, over time, the joint will end up wearing out sooner.
That’s not to say you shouldn’t do them at all, just don’t do them with anything more than a light weight. The more weight you use, the more imbalanced the forces on your knee will be. When I used to do extensions and leg curls (I don’t do them at all anymore), I did light weight and used them as warm-up exercises to lubricate my knees.
So if you aren’t supposed to do extensions or leg curls, what should you do to work your legs?
- Front Squats
- Power Cleans
- Straight Legt Deadlifts
- Good Mornings
All of these exercises are fantastic for the legs, and for the rest of your body as well.
I know there’s some muscle-head with tree trunk legs grunting through a set of leg extensions right now. And you want to look like him. But guess what? He’s in his 20s and the damage he’s doing will take a while to show up. Let him keep doing his extensions. Then look him up in 10 or 15 years and ask him how his knees feel…