T Nation

Safety of Leg Extensions


I believe that most of the big guys on here and almost all pro bodybuilders use leg extensions in their leg training.

My question is, are leg extensions as dangerous as I have been lead to believe by articles written by physical therapists and trainers?

I've read about the stress that leg extensions supposedly put on the patella, patellar tendon and ACL. Is there truth to this or is it mostly crap?

here is an article i read recently


Leg extensions are one of the most criticized exercises out there, but what is the reality?

At terminal extension (near the top), the shear stress on the ACL and the knee joint is at it’s highest. Furthermore, moving down with load to near full flexion, or as close to it as you can, can also impart some interesting loading forces on the knee.

What is generally recommended is that you work in about a 40-60 degree ROM, only getting up to about 5-10 degrees short of terminal extension.

Practically speaking, go high with the knee extension, but don’t lock out. Control the weight on the way down, but only to the point where you still feel tension/contraction in the quadriceps; don’t let them slack off as this is where the passive tissues of the knee joint will have to maintain stability (not so good).

More shortly…


Loading with the leg extension provides one of the most unique evaluations of muscle recruitment.

Generally it was thought this primarily recruited VL and RF (vastus lateralis and rectus femoris).

What has been shown recently is that up to relative intensities of about 75-80% 1 rep max, this is generally the case (VL more active than VM). However, once loads start to go above this, the relative balance of VL - VM recruitment is generally comparable.

Obviously manipulation of the foot angle, which means you are influencing the level of hip rotation, will influence the relative musculature recruited.


Good posts above.

I’ll put it this way. I’ve included them lately in my routines, but I won’t subject my clients to them.


%1RM VL%max VM%max
20% 23.27 16.35
40% 53.70 36.46
60% 68.97 51.80
80% 90.11 88.85

This is some data from a subject I tested the other day who had a 180kg max squat, but here we tested him on leg extensions at different intensities. This is the relative amount of muscle recruitment (using EMG) at different strength levels on the leg extension. This subject generated nearly 400Nm of torque for their maximal leg extension (single leg), so he is pretty freakin strong. This data represents what you often observe for the balance between VL and VM at different relative lift loads.


In a rehab context, the debate is generally closed kinetic chain exercise (squats/lunges etc) vs open kinetic chain exercise (leg extensions), with something like leg press being a grey area (people argue it for both).

The prevailing opinion used to be that leg extensions were horrible and evil.

However, in recent times good studies have come out showing that using appropriate leg extension training actually allows a more rapid restoration of quad strength compared to closed kinetic exercises.

In my experience, people in a rehab context often have so many other issues that hinder their ability to do closed kinetic chain exercises properly, that a correctly performed leg extension works really well.

This is often an exercise that can provoke pain/symptoms; if so, let common sense prevail and do something else.

SO, in summary, if done correctly and you’re not reaching terminal extension, or kicking the weight up and catching it at the top, then letting it drop all the way down and rebounding like a rubber band, the leg extension rocks.


Gluteus, I nominate you for 09 member of the year, though there’s not much competition.

It should also be noted that those in rehab are usually lifting such light loads that the “stress” isn’t that bad, since they are at least getting some quad activation going on.


Glute, what do you do for a living?


[quote]jehovasfitness wrote:
Gluteus, I nominate you for 09 member of the year, though there’s not much competition.[/quote]

Nice backhand complement.


[quote]asusvenus wrote:
Glute, what do you do for a living?[/quote]

Just a trainer, with all kinds of weird experiences (see the Man Above Thread for some of those) who has read a few books. Nothing so exciting as the guys off jetsetting the world with guns in tow…


Gluteus makes a good point about that. I do think much of the sheer force during lockout comes from the upper thigh being forced down into the seat by the load. Some bodybuilders make the habit of pulling with the hip flexors just enough to unweight the thighs during lockout. This does reduce the sheer force some, but is hard to do with a heavy weight. His idea about avoiding the last 5 or 10 degrees while going heavy sounds reasonable.

Now that the subject has started, I recently made some good gains on leg extensions by switching to a toes pointed down version. I’m guessing this way recruits more fibers? In the past I would always curl my toes and feet up toward the shin like you would during leg curls. Anyway, I now notice a huge stretch and since I warm up with leg extensions before squats I notice the pump and warm up is much quicker.


Bodybuilders do a ton of leg exercises that generally include squats, leg presses, deadlifts and lunges. Their glutes posterior chain and muscle activation gets a ton of work. They generally use leg extensions as an accessory exercise higher reps and lower weight doesn’t stress their patella, as much as the average two weeks a year gym goer who wants to come in and do leg extensions instead of squatting. Or young kid who wants to do everything to the max and wants to do a 1 rep max 400 lbs to show off to his friends and strain is patella.


Yea, I figure if I keep the reps above 8 or so and not lock out I should be fine.


I love 'em and so do my historically-problematic knees.


[quote]Iron Dwarf wrote:
I love 'em and so do my historically-problematic knees. [/quote]