In this article, we’re gonna be looking at how to do Leg Extension & isolate the quads with perfect technique but before we get into that let’s take a quick look at some basic quad biomechanics first.
So the quadriceps as the name implies are made up of four muscle heads. Going from medial to lateral or inside to outside you have the Vastus Medialis or tear-drop muscle Vastus Intermedius and Vastus Lateralis or outer sweep and then lying on top of those is the more superficial rectus femoris muscle which is the only head of the quads that crosses both the hip joint and the knee joint.
So the three Vastus muscles have only one function to extend the knee, while the rectus femoris head has two functions knee extension and hip flexion as it crosses both the knee joint and the hip joint and it’s this rectus femoris head of the quads that you probably feel getting a pump when you do hanging leg raises.
So when it comes to hitting the quads since all four heads contribute to knee extension the best thing to do is use exercises that train knee extension.
I think the best exercises here are squat variations like the standard barbell back squat and the front squat might be an even more ideal option. As one 2015 study found that it presents a similar training stimulus to the back squat despite requiring a lighter load, which might reduce injury risk over time.
Now in general I recommend kicking off any quad-focused workout with some kind of heavy compound multi-joint movements like the squat, the front squat, or the hack squat.
Now because the leg extension only acts on one joint it actually has a pretty limited capacity for overload meaning it should be loaded in a higher rep range around 12 to 20 reps and since the ability to overload is more limited rather than focusing on steadily increasing the weight over time we’re going to instead focus on progressively overloading through three other avenues.
How to progressively overload the leg extension
- Improving the mind-muscle connection over time
- Mastering or Improving technique over time
- Improving the pump over time, and one way to do that is to just add an extra rep when you can’t.
Now of course you can increase the weight once you reach the top end of a rep range such as 20 reps or more however at a certain point further weight increases simply going to result in form breakdown and at that point, I think you should just focus on using those other three overloading options.
Why do leg extensions at all?
Well as an isolation exercise their main purpose is to accumulate more training volume for the quads without creating much of a recovery demand for other muscles or joints, in other words trying to build your quads at a higher priority than other muscles might be difficult if all you do is heavy compound lifts and some degree of isolation may be necessary to really optimize their development.
Also, many people seem to be under the impression that leg extensions are an inherently dangerous exercise because of shearing forces and increased ACL stress potential.
However in a comprehensive interview on this dr. brad Schoenfeld states that they shouldn’t have a detrimental effect on someone with healthy joints and he’s seen no evidence of increased injury risk from doing leg extensions.
Obviously, if they give you knee pain and you shouldn’t do them also including a balanced ratio of the quad to hamstring isolation work should further reduce that risk of ACL stress.
Okay so for the leg extension itself there are three cues I like to use to target different aspects of the quads.
3 Cues for leg extension to target different aspects of quads
1. Position the seats slightly back
Position the seats slightly back so the hips are at an angle greater than 90 degrees. If you move the seat all the way up to the point that your hips are flexed to 90 degrees that rectus femoris head of the quads is going to be shortened at the hip meaning it won’t be able to contribute as forcefully to extension at the knee due to active insufficiency.
In other words, because it’s already contracted a lot at the hips it can’t contract as much down at the knee.
Now as for how far to set the seat back, I think that’s something you should experiment with yourself. I personally find something between 60 and 45 degrees of hip flexion to be the sweet spot to get all four heads involved.
2. Pull your butt down into the seat
This is going to lock you into the Machine and prevent power from leaking out of the system.
Also if your butt is popping up, chances are you’re not going to be able to get a full flexion and extension range of motion as they’re likely going to be cheating the range of motion a bit short at the bottom.
3. Point your toes either straight ahead or slightly in
Now I would say that beginners should just point their toes wherever it feels most comfortable.
2 independent EMG studies both found that pointing the toes in resulted in a more Vastus Lateralis or outer sweep activation, so if you’re trying to get your quads to balloon out from the sides more creating that x-frame quad sweep and I think pointing your toes in might make sense.
When it comes to the other heads there doesn’t seem to be much worth mentioning here when it comes to toe position so as a general suggestion I say either straight ahead or slightly in.
Most Common errors while doing the Leg extension:
So I would say the most common error that I see on the leg extension:
1. Half repping the range of motion
Many people just bounce with the weight only going about half the way up which is usually a sign that you’re going too heavy and others will set the pins up so high that they’re only able to do the top half of the range of motion.
Now both of these are basically ways of cheating and they’re gonna rob you of your true quad-building potential.
Now it’s probably worth mentioning that some people do feel knee pain if they go into deep knee flexion at the bottom or full and the extension at the top so if you are in that boat it’s definitely acceptable to restrict the range of motion to what you’re able to do without pain.
2. Not exerting yourself hard enough
Many people treat the leg extensions as a sort of fluff exercise, they just tack on at the end of a leg day while they wait for their friends to finish up and while this really isn’t an exercise you should be hyping up for all across the gym.
You should make sure you’re actually pushing your quads close to fatigue not just going through the motions with no real intensity at all and I do find that this exercise can actually be a bit misleading with regard to RPE in the sense that even if you have five or six reps left in the tank your quads are going to be burning but you do want to push through and make sure you’re getting within at least one to two reps shy of failure.
There are obviously a ton of other quad exercises like the sissy squat, the lunge, split squat and other alternatives but I really wanted to focus on quad isolation and leg extension exercise in this article and I think a well-done leg extension is about as good as it gets for that. I’m so going to leave it at that for here.