How To Do Single Leg Extension - Tips, Benefits, Variations, Sets & Reps

Single leg extensions are a highly favored gym exercise for building the quadriceps thigh muscles for several reasons. They’re less taxing than squats and deadlifts, comfortable since you’re seated upright, isolate just the quads muscles, and you can adjust the resistance and use drop sets to blast your teardrops.

These are all of the benefits we will go into greater detail with later in this exercise guide, plus we included the best variations, optimal sets and reps, and how to get the best gains with this classic movement.

In This Exercise:

Target Muscle Group: Quadriceps
Type: Hypertrophy, strength
Mechanics: Isolation
Equipment: Leg extension machine or alternative
Difficulty: Beginner/intermediate

How To Do Single Leg Extensions

Before you hop on the machine and start slamming out rep after rep of single leg extensions, make sure that your technique is on point and you’ll get the best results that way. See the step-by-step instructions below to check your form.

Step 1: Getting setup

First you want to sit on the leg extension machine and adjust it to fit your body. The most important thing is to keep the foam roller pad of the moving arm at the lower shin just above the foot. You may need to adjust the arm and the backrest to ensure it stays in that spot through the exercise.

Step 2: Brace and engage

Before you do a rep, tense your core and push your shin up against the roller to engage your quads. Now you’re ready for extensions.

Step 3: Leg extension

Starting with either side, extend your leg out and squeeze the quadriceps muscle hard at the top. Slowly drop your leg down and continue for the desired number of repetitions. When you’re finished, switch legs and repeat.

Check out the following video example for a demonstration of single leg extensions.

Benefits

Here’s a list of the good things about single leg extensions.

Isolate the quads

One thing about leg extensions that separates it from other leg exercises is it’ll isolate your quads like no other. It should be your mind-muscle connection exercise of choice because you can really focus all your attention on creating that sexy teardrop!

Less taxing

While squats, deadlifts, and leg presses are super exercises, they can be pretty exhausting. Leg extensions are a good option for when you have little energy to train but still want to stimulate the quads without having to do a full body movement like the aformentioned examples.

Great warmup before big lifts

While you should do progressive sets on the big exercises like squat and deadlifts, leg extensions are a non-exhaustive way to get some blood in your knees and prepare them for the subsequent movements.

Drawbacks

Here are some not so good things about single leg extensions.

Can jack up your knees

Save the ego lifting for squats and deadlifts, not leg extensions. Yet many choose the heaviest weight and barely extend their knees or do short pulsing motions. These type of exercisers probably know they shouldn’t be doing that or they don’t understand how dangerous this can be for their knee joints. Jerky movements, and swinging the weight up with your knees is also just as bad.

Quads-only

Unfortunately, leg extensions don’t work the glutes and hamstrings as well as they do the quadriceps. These other muscles get some stimulation but nothing to write home about. Extensions are a quad-dominant exercise.

Common Mistakes

When we say you don’t want to make these mistakes, there’s more risk involved compared to other exercises.

Loading too much weight – Whether you use a weight stack machine or a manual loaded variation, you DO NOT want to use too much weight (relative to your strength ability or even in general) on leg extensions. The reason is very simple. It’s just your knee hanging out there unlike a closed chain exercise (e.g., squats) where the whole body provides support to execute the movement.

Leg extensions can be a beneficial exercise but we’d caution against using the full weight stack even if you’re capable. We recommend using a weight that will become challenging after about ten reps or so, and doing higher rep sets for the sake of your knees.

Ideally, single leg extensions will also not be the primary quad building movement in your leg training routine.

Terrible technique – There’s a difference between proper cheat reps and using momentum to lift a weight. You’ll often see excessive swinging and rocking but are the muscles being worked? Well, that’s debatable. The other thing is forgetting you have knees. Heavy weights and crazy form can mean disaster for your knee caps.

Variations and Alternatives

Check out these similar exercises that will accomplish the same goal but offer their own advantages. Some are variations while we also included some alternatives for when you don’t have access to a leg extensions machine.

1. Leg extensions (two legs)

Some people prefer to do the standard leg extension variation using both legs at the same time. The only benefit is that you’ll be able to lift more overall.

2. Leg extensions w/ resistance band

If you have a training bench and some loop resistance bands, then you can do leg extensions without needing a dedicated machine.

Wrap one end of the band around either leg of the bench and then pull it to the other side and under the opposite end where you’ll sit during the exercise. Place a foam roller or some type of padding under your knee to elevate your leg and then insert your foot in the band. Now you have makeshift leg extensions!

That’s just one example, however, you can do this exercise several different ways and using a variety of things or setups. A chair will also work.

Here’s an example of how you can single leg extensions using a band.

3. Bodyweight extensions

No bench, no worries. If you don’t have access to a leg extension machine, you can do a few body weight variations. There are two main versions that work excellently and they each have their own advantages. Check out the below video for a detailed demonstration of both leg extensions.

4. Sissy squat

A legendary exercise used by many of the greatest bodybuilders, sissy squats are an underrated quadriceps focused exercise. They’re also very challenging and a great option for bodyweight only training.

Check out our review of the 10 Best Sissy Squat Machines for 2022.

How To Program Single Leg Extensions In Your Workouts

There are two very good ways to incorporate single leg extensions in your workout. Those are before (first exercise) or after a workout. If you place them first in your session, you’ll warmup the knees before the compound variations like squats for example.

But now flip and reverse that… if you throw in a few sets of leg extensions after a workout then your knees will already be warmed up from those bigger multi-joint movements. This is the opportune time to shoot for drop set training to really blast your quadriceps.

Sets/Reps

Note: Leg extensions should not be used as a pure strength-focused quads exercise. The potential damage to your knees is simply not worth the risk in our opinion. Select a reasonable amount of resistance and never try to do a max weight repetition.

We recommend 2-5 sets of 8-30 reps depending on your training experience and goals. Aim for lower reps to focus on strength and hypertrophy and a higher rep range for hypertrophy and muscular endurance.

Muscles Worked

Single leg extensions are a quadriceps movement, however, other muscles are still involved or they still perform an action although not to the same extent as the quads muscles.

Quadriceps – The quadriceps make up most of your thigh mass consisting of four muscles – rectus femoris, vastus lateralis, vastus medialis, and vastus intermedialis. Its job is hip flexion and knee extension such as when you perform a squat or walk up a flight of stairs.
Hamstrings – One less head than the quadriceps muscles, your hamstrings have semitendinosus, semimembranosus, and biceps femoris heads. Anatomically, hamstrings are on the other side of your quadriceps and functionally, they extend the hips and flex the knees. The short head of the biceps femoris only crosses the knee joint.
Core – The core consists of your abdominals (muscles used to crunch), obliques (muscles on the outer torso that help us twist side to side), deep core muscles (transverse abdominis and internal obliques that stabilize the spine), and back extensors (allow us to stand up straight from a bent-over position and lean backward). We naturally tense these muscles during single leg extensions.
Sartorius – If you ever wondered what is the longest muscle in the human body, it’s the sartorius muscle that crosses both the hip and knee joints of which it assists in the flexion of both. It also externally rotates the hips.

Bottom Line

If you take special care to avoid overloading your knees then single leg extensions can be one of the most desirable exercises in your leg training regime. They’re not just a beneficial muscle builder but an exercise everyone looks forward too because you’re seated in a comfortable position and an insane muscle contraction in the quads is a guarantee.