Leg Extensions vs. Squats

[jwcalla]

I'm interested in getting some opinions (or science) on a topic. Between the two exercises -- leg extensions and squats -- which one would recruit more muscle fibers in the quadriceps and place a greater tension load on those fibers?

John

[Scott Ismari]

squats hands down....

Squats are a compound move activating the quads at two joints ( hip and knees) This causes a more powerful contraction, moving more weight ( yes I know there are other groups helping in the squat).

Leg extensions are an isloation move, using the knee joint only, activating the quads from one point only.

Commom sense dictates that the movement at which you move the most amount of weight ( squats) makes the strongest contraction and offers the greatest stress load.

If you are talking Torque...the leg extension actually places more shear stress on the muscle because of the pivot point at the knee...more potentially dangerous and less effective as the squat if both are done in the same manner of execution ( quality of form).

Im sure others will go into more scientific detail however I chose to keep this post on a more laymans term....you can always get the details in the kenisiology section of this site.

[Stephen Johnson]

I'm interested in getting some opinions (or science) on a topic. Between the two exercises -- leg extensions and squats -- which one would recruit more muscle fibers in the quadriceps and place a greater tension load on those fibers?

John

I did a google search to resolve your question, but I didn't come up with any articles that tried to quantify differences in muscle fiber recruitment between the two movements.

However, the articles that I did see were overwhelming in their preference of the squat over the leg extension as an exercise. This is even true for rehabbing knee injuries - a sharp reversal of what I used to see 10 years or so ago. This is a typical analysis:

Note that this research suggests that for individuals with anterior cruciate injuries, squats should be safer than isokinetic or isometric extension for quadriceps strengthening (leg extension), since forces acting on the ACL were lower during squatting, compared with both isokinetic and isometric extension. Yet, individuals with ACL injuries are often told to eschew squatting for extended periods of time - and instead work on leg-extension machines which actually may place more stress on the anterior cruciate ligament. For those with ACL problems, isokinetic flexion, isometric flexion, and squatting may safely be used for strengthening of the hamstrings, but note that isokinetic and isometric flexion are less 'functional' than squatting, i.e., they fail to duplicate the weight-bearing, synchronous multi-joint movements associated with sporting activity

.

And, for healthy individuals, squats lead to greater increases in usable strength than leg extensions.

Some bodybuilders use leg extensions to pre-exhaust their quads before squatting, and others use it as a finishing movement after squatting. But no bodybuilder has ever gotten contest-quality legs just by doing leg extensions.

[Matt Z]

I would even question the value of Leg Extensions as a assistance exercise to improve squatting. I think Leg Presses, Lunges and Step-ups are all better choices as assistance exercises.

[Kenny Croxdale]

I'm interested in getting some opinions (or science) on a topic. Between the two exercises -- leg extensions and squats -- which one would recruit more muscle fibers in the quadriceps and place a greater tension load on those fibers?

John

Leg extensions are a worthless exeercise. Only in limited situation would they ever be performed.

Leg extensions place a lot of shear force on the knees.

Kenny Croxdale

[jwcalla]

Thanks guys for all the info. It's appreciated. And fear not, I wouldn't dare replace squats with leg extensions. I used to do them as an auxiliary exercise, but as many have mentioned, I found them to cause some knee pain.

I was just looking for something to hit the quads a little better, especially the lower quads where there seems to be a disproportionate lack of bulk (like above the knee area -- 4th and 2nd heads). And I've noticed that I tend to get a better contraction/flex throughout all the heads on leg extensions so that's why I was wondering if it recruited more fibers. But I'm probably going to stay away as I don't need any knee problems.

John

[Ironman]

I would use hack squats for quad isolation. It's great for supersets and prefatigue too. There is a machine, but I just use a barbell. It's like a deadlift with the bar behind you if you aren't familiar with it.

[Oscar]

I was just looking for something to hit the quads a little better, especially the lower quads where there seems to be a disproportionate lack of bulk (like above the knee area -- 4th and 2nd heads). And I've noticed that I tend to get a better contraction/flex throughout all the heads on leg extensions so that's why I was wondering if it recruited more fibers. But I'm probably going to stay away as I don't need any knee problems.

John

Can you really target like this? I thought this was more down to your genes than choice of exercise.

[TimD]

Targeting may put adifferent emphasis on things, but I think you're right, genes are the most important. I do think , however, that just due to the mechanics of the lift (i.e the torso is more erect) , front squats are probably the exercise (include Zercher-your just holding the bar differently) for what the poster is asking about, the tear drop above the knee. Just look at any O lifter thats been training for some time, they have very visible tear drops The PL style squat, while an excellent exercise for all over size and strength, shifts emphasis to all over the lower body, and has less quad involvement.
Tim