I don’t know of any muscle building exercise out there that gets more blatant hate than the leg extension machine.

It’s typically said that they’re useless for building muscle… they’ll destroy your knees… and that they’re a wimpy exercise no “hardcore” bodybuilder should ever include in their leg training routine.

But all the macho chest-thumping aside, what’s the real truth here?

Let’s tackle the main questions…

Are Leg Extensions Useful For Building Muscle?

When it all comes down to it, any exercise that allows you to place consistent tension on the targeted muscle and that allows for a progressive increase in resistance over time will result in muscular hypertrophy.

The leg extension allows you to accomplish both of these things, and so yes, it certainly will add size to your quads over time.

Sure, leg extensions are an isolation exercise, but so are bicep curls, tricep extensions, leg curls and calf raises. Nobody has a problem with the idea that these exercises are effective for building muscle, so I’m not sure why the leg extension tends to be viewed differently.

Now, let me make a few things clear here…

First off, there’s absolutely no question that the foundation of effective quad training lies in heavy compound exercises such as squats, leg presses and lunges.

Obviously you should never be performing leg extensions as a primary quad exercise or in place of any of these basic bread-and-butter lifts. If you are going to include leg extensions in your routine, they should always be done at the very end after all of your compound work is done.

Secondly, I’m not saying that you need leg extensions in your routine or even that you should be performing them.

In fact, in most cases they won’t be necessary, and I don’t have them included as part of the quad training routines in my program either.

I’m not even saying that they’re a particularly great exercise, or that they’ll contribute in any big way to your quad training efforts.

ALL I’m pointing out is the simple fact that they can be included as part of an overall quad training routine in specific cases, and that they are definitely not a “useless” exercise like so many people try to say.

Here are a few situations where including leg extensions at the end of your quad workout could make sense…

  • You want to include some additional volume for your quads but your lower back (or just your body in general) is already worn out from your heavy compound lifts.
  • You experience lower back discomfort in general (or are recovering from an injury) and need an exercise for your quads that doesn’t place your lower back at risk.
  • You’re particularly posterior-chain dominant and your glutes/hamstrings tend to take on a high percentage of the work during your compound leg exercises.
  • You want to perform some high rep work for your quads but find that your cardiovascular system becomes the limiting factor when performing compound quad exercises in the 12+ rep range.

These are just a few situations where leg extensions could be a useful addition to your training plan.

Onto the second major question…

Are Leg Extensions Bad For Your Knees?

Although most people will give a black-and-white “yes” or “no” to this question, the real answer is that it depends on your individual body structure, and it depends on how you perform them.

For some people, regardless of how they approach the exercise, they’ll always experience knee discomfort no matter what. I think it’s pretty obvious that in this particular case, the leg extension machine should be completely avoided.

However, if you are able to perform leg extensions without any pain, then they’ll probably be fine as long as you:

  • Perform every rep using a slow and controlled cadence. Never explode out of the bottom position, and make sure to perform every rep under complete control without using any momentum.
  • Use moderate weights for higher reps. Stick to a bare minimum of 8 reps per set on this exercise, and an even higher range of 10-15 will be ideal.
  • Progress very slowly. Don’t make any major leaps in the amount of weight you use from week to week. Focus on very gradually increasing the resistance over a longer period of time.
  • Adjust the machine to the setting that feels most comfortable for you. Everyone’s body structure is different, so make sure to adjust the back pad and seat to an angle that minimizes the pressure on your knees.

If you follow all four of these steps and use some basic common sense then you shouldn’t run into any problems when performing leg extensions in your workout.

You can also optionally cycle on and off them just to go even more on the safe side. For example, 6-12 weeks on followed by 6-12 weeks off.

Final Word On Leg Extensions For Building Muscle

The purpose of this article is not to encourage you to perform leg extensions in your routine or to claim that they’re a necessary part of an effective overall quad training workout.

Rather, I’m simply pointing out that…

1) They are definitely not a “useless” exercise, and they will allow you to add size to your quads over time if performed properly. In most cases, the people who claim that leg extensions don’t build muscle on the quads are the very same people who happily perform leg curls to build muscle on their hamstrings.

2) They can be included at the end of your quad workout if they don’t give you any discomfort, and if you have a specific application for them, such as lower back fatigue from your compound lifts, a lower back injury, posterior-chain dominant body structure or if you just want to perform additional high rep work for your quads.

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