Leg Extensions – The Stupidest Exercise Ever Created?
Leg extensions have been maligned by the strength and performance community. Similar to the arguments made against the hip thrust where I actually sided with the use of this controversial movement (see my article here).
Some of these arguments are (taken from the entire interwebz from many different articles (I will cite two): 
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- Increased joint stress
- Reduced hamstring activity
- Reduced VMO (vastus medialis oblique) activity
- Contributes to lazy adductors, abductors, and hamstrings
- Constant tension on the ACL
- No carryover to any closed chain movement. A closed chain movement is when the feet are closed off to the ground, like the squat. Open chain is limb-intensive and leaves the feet “open,” like a leg extension
The deviation I have from most strength and performance coaches is that not only am I a speed and strength specialist, but I have also competed as a professional bodybuilder. Hypertrophy, not performance, was my priority.
While I feel the good bros in the gym are speaking nonsense when they tell people to do leg extensions and not squats if they have bad knees, I also feel that strength coaches and science nerds, while science is on their side, are disconnected from hypertrophy.
Sometimes, as much as it pains me to say it, science has to play well with anecdotal evidence. A lot of big a$$ legs have been built on programs that include a healthy dose of leg extensions. We cannot overlook this reality.
From Dorian Yates to many others, leg extensions create overload, and overload leads to hypertrophy. Will it help you run a faster 40-yard dash? Probably not. But can it help you build big quads?
Well, it can't hurt.
But... We also must account for risk versus reward since leg extensions do kinda suck for safety. Let’s dissect these objections one by one to see if there is any merit and if that’s reason enough to drop them from your program.
Are Leg Extensions Dangerous?
Increased joint stress
Studies have shown increased joint stress caused by the leg extension over closed chain movement and full range of motion (ROM) squats.  While one would think that the squat is worse (full ROM with weight on your back), it isn’t.
Not only does data back it up and also finds that deep squats “may actually be an effective method of preserving joint health,” but from an evolutionary and primitive standpoint, we have to squat to poop, which is necessary to live…
Unless of course you like carrying pounds of poop in your belly at all times – humans didn’t always have toilets. While I don’t normally poop with 315lbs on my back, the movement is natural. Our ancestors didn’t have to leg extend to hunt wooly mammoths.
While leg extensions increase joint stress, they also do a phenomenal job of placing a direct load on the quadriceps. Is it equal load? No.
Is it worth the strain on the knees? Maybe and maybe not, but for pure muscle growth needs, the leg extension checks off the “load” box, so let’s assume weight isn’t maximal and you are simply adding load? Our joints undergo stress every second of every day, even sitting down stresses joint.
Is it as safe as a squat? According to science, no, it isn’t. But is it as bad as some of my colleagues make it out to be? My opinion is no. It might help to compliment a more compound movement, like a squat.
Reduced hamstring and VMO activity, and contributes to lazy adductor and abductor muscles
We dove into this on the hip thrust article. This is 100% true. When you target your quadriceps with an isolation movement like the leg extension, your hamstrings aren’t worked equally.
Freaking brilliant observation strength-experts. 
As for decreased VMO activation, lazy adductors and abductors… When done alone, YES leg extensions can delay firing of this muscle, and this is something that is endemic to knee injuries, but I am assuming even the most bro of trainers would have their client do at least a leg press and hopefully a form of the squat.  Thus, who cares?
Assuming one doesn’t do leg extensions as their only leg movement, I wouldn’t pay this any attention. Geez, you strength guys are so black and white!
Constant ACL tension
Yeah, um... This one I cannot refute.  The leg extension sucks, I guess, maybe. But all exercises stress joints.
Show me an elite powerlifter who can walk properly in their 50s.
Ed Coan probably didn’t do many leg extensions in becoming arguably the greatest powerlifter of all time, but he has two artificial hips. He did what my fellow strength “experts” hold near and dear as the functional “king of all exercises” – the squat!
To induce trauma, stuff gets weird.
Like I said, squatting is primal. Squatting with 315lbs on your back isn’t. While it stresses your knees, it overloads the muscle. Is it optimal? NOPE. Is it akin to trying to circumcise yourself with a wooden spoon? Absolutely not.
No carryover to closed-chain movements
The expert reasoning goes like this. If you squat more, you will have stronger leg extensions. If you leg extend (not sure if this is even a word) more, you don’t necessarily squat more.
Therefore, there will be no carryover into sports or performance.  Why? Because, science.
Last time I checked, the good bro reading this article interested in having meaty quads doesn’t care about his 40-yard dash or shuttle time. For performance, I agree. For the common mirror-loving gym rat, nope, not gonna agree.
The Case for Leg Extensions
When training my soccer players we will never do leg extensions, ever. There is no need.
I don’t care how awesome their legs look in shorts, I care about speed and strength.
But for bodybuilding, or just looking good, while not a great movement, and I don’t even do them myself, they are an option that might help add some inches on your quads.
The problem with the strength and performance community is that they put everyone in a bubble. We all don’t have the same goals, and being black and white does nothing for anyone, it just divides camps.
I am not a zealot, nor am I selling programs. In fact, all of my articles and books are FREE at TigerFitness.com. I just want YOU to have the information you need to help you reach your goals.
Leg extensions, yes or no? For me, no. But if you like the pump, and if you feel they will help you, ENJOY them in conjunction with other more compound movements.
Be wary of too much weight and if it hurts in your knee stop. If your main goal is performance in any sport, perhaps you should avoid them. But, as always, it depends on you and there is no one-size-fits-all program.
Now stop reading and go build some QUADS!
1) Eric Cressey, T Nation. "The Truth About Leg Extensions | T Nation." T NATION, www.t-nation.com/training/truth-about-leg-extensions.
2) Haley, Andy. "Why You Should Never Do This Exercise." STACK, 29 Apr. 2014, www.stack.com/a/never-do-leg-extensions.
3) Clin Biomech (Bristol, Avon). 1999 Jun;14(5):329-38.
4) Shrugged Collective - A Fitness Network from the Creators of Barbell Shrugged, shruggedcollective.com/wp-content/uploads/2015/04/DeepSquat-Review-Barbell-Daily-3-27-15.pdf.
5) Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk KE, Andrews JR. Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc. 1998 Apr;30(4):556-69.
6) Stensdotter AK, Hodges PW, Mellor R, Sundelin G, Hager-Ross C. Quadriceps activation in closed and in open kinetic chain exercise. Med Sci Sports Exerc. 2003 Dec;35(12):2043-7.
7) Chow JW. Knee joint forces during isokinetic knee extensions: a case study. Clin Biomech (Bristol, Avon). 1999 Jun;14(5):329-38.
8) Stiene HA, Brosky T, Reinking MF, Nyland J, Mason MB. A comparison of closed kinetic chain and isokinetic joint isolation exercise in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther. 1996 Sep;24(3):136-41.