Tuesday, February 12th, 2019

Are 90 Degree Leg Extensions Bad for Your Knees?

After cross referencing a number of sources, I've come to the conclusion that 90 degree leg extensions may put too much stress on the knee joints.

Apparently, this is not news in some circles as many bodybuilders have believed this for years.

Here is a video from Scooby on YouTube demonstrating this.

Scooby has a number of work arounds for different kinds of leg extension equipment both at home and at the gym.

It mystifies me why so many gym equipment manufacturers don't have an adjustment for the bottom leg roller so you can angle it upwards.

Leg Extensions

There are of course some that do but their machines are very expensive and the ones I've seen are dedicated machines not home gyms.

Scooby recommends pulling the pin out of the weight stack machine at the gym and angling upward the bottom leg roller and if you can reach the pin while holding the roller up that's great. But on my home gym, my arms are just not long enough to pull up the bottom roller and reach over with the other hand and put the pin into the desired slot. With someone there with you then that would work great even at home.

Another way to lessen the stress on the knee joint comes from internationally known Dr. Michael Yessis. You can read about it at his website under the execution section. Essentially Dr. Yessis says to start the leg extension at a wider angle and then you only put extra stress on the knee joint on the first rep. You never lower the leg extension roller to 90 degrees again while performing your reps/sets.

So after looking at numerous leg extension/leg curl machines with an adjustable cam I decided I didn't want to spend the money on a dedicated machine.

I went to the hardware store and bought about 24 inches of chain rated at 300 lbs and two threaded oval chain connectors rated to at least 210 lbs. My Body-Solid EXM3000LPS has a 210 lb. stack for the leg extensions.

Then I disconnected the bolt and bushings that connects the cable to the lower roller. I connected the oval threaded chain connector to both ends of the chain and put the bolt and the few bushings back into place where it attaches to the bottom leg roller. Since the chain connectors were about 2 inches each I only connected about 21 inches of the 24 inch chain.

Works like a champ! Plus you have the benefit of resting between sets as you don't have to support the weight at the wider angle when you want to rest.

This modification will put slack into the leg extension about up to the half way point so children could pinch their little fingers and hands. Just be careful!

This works on the Body-Solid EXM3000LPS home gym, not sure about everyone's home gym. Again be careful if you attempt this and do it at your own risk.

I love the way this works now as everything functions normally.
It's far better than taking up more space with a dedicated machine.

Again this is a call to gym manufacturers everywhere to incorporate an adjustable lower leg roller into their machines to save our knee joints. - Jack

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2 Responses to “Are 90 Degree Leg Extensions Bad for Your Knees?”
  1. get smart says:

    What does this mean for you? If you suffer from joint pain or previous joint injury, you should try to avoid open chain exercises at that particular joint. So, if your knees are bad, do squats and lunges (closed chain exercises) instead of leg extensions or leg curls (open chain exercises). If you injured your elbow, do pushups (closed chain) instead of chest presses (open chain); if you have shoulder issues, try pull-ups in lieu of overhead presses, and so on.In general, the knee joint is the most vulnerable joint in the entire body. So it’s a good idea to limit the amount of open chain exercises you do for the lower body—especially with heavy weights—to prevent problems from occurring in the first place. Personally, I think this gives even more reason to vary your exercise program. I do both open and closed chain exercises, but I NEVER perform any open chain exercises for the lower body unless it involves little to no added weight. That means that I do not use machines for leg extensions or hamstring curls, because the added weight and the position of that weight (again, on the “distal” part of the leg) is risky for the already-vulnerable knee joint. Squats and lunges are some of the best exercises you can do anyway, so those are my go-to exercises for the lower body. Since the joints of the upper body aren’t as prone to injury as the knee is, I do both open and closed chain exercises, but I try to vary between the two on a regular basis. How about you? Will you avoid open chain exercises now that you know the difference?

  2. iFitnessGuy says:

    My knees are a bit weak, and when doing leg extensions, i’m afraid of going heavy most of the time. I find myself doing a decent weight with may reps

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