So whats the real deal, have the time I hear it’s bad for you, half I hear its fine for the knee. Does anyone know of any studies/articles that back up the theory that it’s bad for your knee?
I did them for years with no problems. The one good point about them is that they load the knee at full extension so you can develop strength at this position in the range of motion (which you could argue is very important since when you run you load the quad with the knee straight, all be it eccentrically) plus if you ever injure your feet and can’t squat you can maintain strength in your legs.
However, when I developed a knee problem (Q-angle problem) they became very painful. I tried physio, no help what so ever. But then when I got EMS i used it on my quads at full extension and amazingly the pain subsided in only a few weeks. So now I never use them. I use EMS for strength at full extension.
I think the design of the machine does make a big difference. I used a MedX testing machine for some months and it was amazing compared to the others I have tried (very smooth and no discomfort at all) but it costs $30,000 so you won’t find it in many gyms.
I guess they could cause a lot of problems if you don’t lift the weight slowly as the momentum at full extension could do some damage. Apart from that, my experience is neutral but i think EMS is better for quad development.
see I had always heard that they were worst thing for your knee because they pulled on the patealla
Pulling on the patella? Well obviously this will happen because that is what the patella is for (increasing the mechanical advantage of the knee joint by acting as a natural cam).
Since you almost never load your quads in full extension during normal everyday activities I can understand how jumping in and performing leg extensions with a heavy weight could lead to problems if you don’t build up gradually. Plus unless the cam in the machine has a pretty hefty fall off at full extension you will have to slam your leg into extension in order to make the last few degrees of ROM with a weight that feels fairly managable during flexion (so machine design does matter).
There is probably truth in the exercise pulling on the patella because that would explain why it hurt when my patella wasn’t tracking correctly (and this pain was only felt 10degrees from full extension).
How could you use leg extensions in a program? Well I would say use it as an auxillary exercise, keep the reps above 6 and make sure you squeeze into extension smoothly so as not to impose too create a high stress peak (from momentum) on that area. Is it integral to your program? Not really, but you could use it for a few weeks for a change of scene.
You aren’t supposed to extend your leg fully. If you lock out it can damage your knee at high weights I believe.
A physical therapist told me that it compresses the patella into the tendon too much. Not sure if it’s true or not.
Some traininers say it overloads the VMO causing it to pull on the patella! Doas anyone know if this is actually true?
Yes, if you don’t do it properly. If you use a leg press machine, the angle of your knee should not be less than 90 degrees, and you shouldn’t let your leg fully extend to the point of locking.
Leg Extensions on a machine where you sit down and then do a leg extension is “VERY VERY BAD FOR YOU!” However; if your recovering from a knee injury such as an ACL or MCL I believe that leg extensions are good for you but only with light weight. So this doesn’t mean to load that mofo up!
If you aren’t rehabing then avoid this exercise as the plague!
The question you need to ask yourself is why aren’t you squatting!
Ok but why are they bad for you? This is what I’m searching. I’m having an arguement with a guy at work and I say there bad for you but I can’t find any scienetific backing
I think its bc of the pressure put on the patellar tendon. Think about it this way, when you squat all the forces are pulling your patellar tendon either up or down, this includes gravity and also the forces generated by your agonist/antagonist muscles. But at least this way the knee cap (or patella as it is also known by) moves in its proper groove (unless you have some muscle imbalance issues). Now when you do a leg extension, gravity is pulling down on the knee cap so that it will grind more when moves in its grove. Also as someone else mentioned that certain muscle groups will be utilized more than other muscle groups (when compared to a squat); therefore, you are using the muscle groups in a somewhat different manner. This leads to a muscle imbalance issue which will pull the knee cap more in one direction than the other so that it no longer runs in the perfect groove.
Something else to think about. When you do a squat the force of the wt you are lifting generally is in-line with your center of gravity. Now pay close attention to this next sentence. When you are doing a leg extension their is more force acting on your patellar tendon bc the wt is moving away from your center of gravity. What I mean is that as your legs go further away from your knee (remember that at the starting point your legs are directly beneath your knees so that although you are sitting down your legs are still in-line with your knee) the greater is the force that is acting on your patellar tendon. When your squatting the forces are minimal in comparison to that of a leg extension. Don’t believe me well then think of it this way, when you do a clean do you try to get the bar as close to the body or as far away from the body? Would you rather reverse-curl the bar up? Those were rhetorical questions but the answer should be pretty obvious. The same goes for deadlifting the more you move the bar away from your center of gravity the more force is acting on the back!
From experience, just the opposite! If you have healthy knees, you can safely use the leg extension, through a full range of motion.
If you have any knee issues I’d avoid it. Or if you do use it, use it only in the top portion of the lift, but there are better options.
just my 2 cents. A mate of mine is a thrower and he injured his knees (not a full injury but he was on his way and had some pain) point is that from squatting he strengthened his outer quad or the lateral head, and was given leg extensions to rehab because it “balanced out the effort” and strengthened the medial head and “realigned” his patella by forcing the quad to distribute the strength in a straight line.
Personally I think that leg estensions are good because they allow you to work with our legs vsibly aligned and there is less possibility for small variations, whereas in squats (which I do love) on occasion you will notice someone squatting and their knees moving in or out during the movement.
hope my opinion helps 
I read an article that talks about the “shearing effect” that the exercise places on the knee. I will dig it up. I discontinued using the exercise for years then rethought. I now do a set with internal rotated hip and external rotated hip. This hits the Vastus lateralis/TBand area or vastus medialus depending on the foot direction. I tend to go lighter than long ago. It has helped my legs. No knee pain if I avoid the normal use. I am not a big fan of heavyweight with the foot straight. Do front squats or lunge with knee over the toes. 2 cents.
please dig it up
basically your thigh is held immobile by the seat, and the load is on the foot. thus there is nothing supporting the lower leg.
Sit in your chair and extend 1 leg so it’s straight
now envision someone pushing down on your shin
what’s happening at the knee.
the unsupported lower leg is trying to pull away from the supported thigh.
This creates a shearing force.
The only thing really keeping the lower leg attached to the thigh is your ACL/MCL/etc…
I realize this is a gross oversimplification of whats happening and it can be tough to visualize without pictures
Yes! This is partly what I meant in my post about the forces acting on the knee. I believe the leg press also creates shear force on the knees.
I was also thinking about this. In your friends case I can see using that exercise to some degree; however, I also had a tight IT band and my knee was tracking to the outside. I fixed this by doing Microstretching as well as getting rehab by doing one legged quarter BW squats with a biofeedback machine! Just trying to point out that there are other options that may present less risk!
I apologize for not finding the article. I believe it was a Muscle and Fitness roughly 1999/2000. It was written by a P.T. I think. Since I live in California and we have had a few tremblers I relate even more. Sheering force is a big issue with bridges when they are upgraded to meet Cali code. If you have a pillar and the force comes directly down on it, like a force coming down on a minicus, then the object/person can readily absorb the force. When to much force is placed on top, the object cracks and sort of implodes. So engineers put large wires on the outside of the post to increase it ability to absorb that force coming down. Roughly like a knee brace. But if the force comes from another direction, defined here as a sheering force it will go through the post and it will have lightning looking cracks. The same goes with the knee if you can see it in your mind. I’m sorry this probably created more q’s than a’s. If you read a little on sheering force, you’ll see some correlations with the human body. I am not an engineer obviously. I agree with SuperNova on the leg press. I think it can also create some low back issues when the lower back curvature is changed. I’m sure there are more qualified people here that can explain that better. Remember the lightning looking type cracks in a wall.
damn I’m try to prove to this guy that i work with that their crap, he knows his antaomy so i need some prefoessional articles