Leg extensions are the perfect quad-targeting exercise for leg day. If you want to learn how to do a leg extension, you’re in the right place. We’re about to show you exactly how with our step-by-step guide and how-to video.

There are tons of articles criticising this exercise which has most people asking ‘are leg extensions bad for your knees?’. We’re here to answer that question and help you see some of the leg extension benefits.

If you’re not convinced that the benefits outweigh the potential risks, we’ve also included tutorial videos for every leg extension alternative that will work your quads just as well.

But first, do you think that you have what it takes to take your passion for fitness further and become a qualified Personal Trainer? See our range of personal trainer courses and certifications here.

What Is A Leg Extension?

how to do a leg extension image

So, this part is pretty self-explanatory, but we’re going to start by ironing out the details. As the name suggests, leg extensions are a leg exercise, and yes you guessed it, you do them on a leg extension machine

A leg extension is a strength training exercise that isolates the quadriceps – the group of muscles at the front of your thighs. For this reason, you might have heard someone refer to this exercise as a quad extension. 

Leg extensions use weight resistance to build the strength and size of the quadricep muscles. So yes technically, they aren’t a total leg exercise, as they only target your quads. Regardless, this exercise is deserving of a place in your leg workout.

If you’re looking for an exercise that will work all of the main muscles in your legs, stick to squats as they target your quads, hamstrings, glutes and your calves. If you want quads that look like they’ve been sculpted by gods, leg extensions are the exercise for you!

How to Do A Leg Extension

If you’re already familiar with the leg extension and you’re here looking for alternatives to this exercise or how to do leg extensions at home, without a machine, bear with us for now! Our list of common mistakes has some key pointers for minimising injury and making sure you’re getting the most out of this exercise. 

If you’ve avoided the leg extensions up to now, we’re about to break down exactly how to do a leg extension on the machine, just for you!

Step-By-Step Guide:

How to do a leg extension image 1

  • Sit on the chair with your back straight and against the back of the seat and hold the side handles.
  • Put your shins behind the padded bar (or roller) and position your feet so that they’re facing forward. The padded bar should be sat on top of your shins, just above your feet (you may need to adjust the machine).

How to do leg extensions image 2

  • Raise the padded bar by extending your quads to straighten your legs.
  • Once your legs are extended, hold this position for one second whilst squeezing your quads.
  • Slowly lower the padded bar back down towards the starting position without letting the weight stop.
  • Repeat!

Reps, Sets & Weight

We can’t say exactly how many reps and sets of leg extensions are best for you, or what weight you should use, that all depends on a number of personal factors like your strength and fitness in general. 

To start, try between 8 and 12 reps for 3 sets. 

A good tip for choosing the right weight on this machine is to not use a weight that’s too heavy. Even if you cando the move with a higher weight, that doesn’t mean that you should in this case. Keep the weight light enough that you’ll be able to stick with it for every set. This will minimise the stress of the move on your knee joints.

If you get stuck, there’s no need to be shy – speak to a Personal Trainer at your gym!

Common Mistakes

Keeping Proper Form 

Proper form is vital in order to minimise your risk of injury. When you’re sat in the starting position, there must be a 90°angle between your upper and lower leg.

If this angle is less than 90°, the knee will be positioned over your toes which will cause excessive stress on the knee joint.

Don’t Overextend 

are leg extensions bad for knees image

Another common mistake that can increase the risk of injury from this exercise machine is overextending the knee. When your legs are fully extended, it’s important that you don’t lock your knees as this will also strain your knee joints.


As with all exercise, it’s important to watch your breathing. It seems silly to even mention, but so many people hold their breath during exercise.

During leg extensions, exhale your breath as you extend your legs and then inhale as you lower them back down.

Leg Extension Benefits


New to resistance training? We all were once, and we get it, free weights can be a bit intimidating if you’re a complete rookie at the gym. 

Because there is an exercise machine exclusively for leg extensions, they’re a really accessible exercise for beginners. Using an exercise machine makes it easier to get your form, posture, and movement right, and so this machine is a great place to start.

Train the Quads in Isolation

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As we touched on before, the leg extensions are great for working on your quads. This is because they are an open-chain kinetic exercise. Open-chain exercises are really effective for isolating a targeted muscle – in the case of the leg extension, this is the quads.

Training your quads in isolation is great if you’re looking to add more definition to your upper leg muscles or if you want to work around a hamstring injury. This is a key benefit as there are not many – if any – other exercises that isolate the quads quite as well as this one.

Build the Size of Your Quads

If you want to increase the size (and strength) of your quad muscles, do leg extensions! Because the leg extension benefits the quads in isolation, they’re great if you want to build the pure size of these muscles in particular.

Alternatively, building the size of your quads is also a benefit for anyone who’s current training emphasises the hamstrings or the glutes and wants to balance out the muscles in their legs.

Benefits of The Movement Itself 

leg extension benefits kicking movement image 

A more indirect, but equally relevant, benefit is that the movement itself is natural and therefore has benefits that can be applied to other sports and activities.

By working your quads with this movement, you can mirror and therefore increase the force of a kicking movement. This is a bonus for those who play sports like football where you use this movement regularly.

Assist the Rest of Your Workout

For obvious reasons, leg extensions are a great way to reap the rewards of strong quads.

The purpose of the quad muscles is to extend your knees, so strong quads have benefits for other exercises which also involve knee extension, like squatting.

Basically, it’s a good idea to train this movement to strengthen your quads and improve your performance in the rest of your leg workout = stronger squats!

Are Leg Extensions Bad for Your Knees?

eg extensions bad for knees image

Leg extensions are infamous for being bad for your knees. This is because the movement places a lot of shear force on to the back of the patella (your knee cap), which forces the tibia (the bone in your lower leg) towards the femur (your thighbone). This can be painful, as well as damaging to the ligaments and the connective tissue in the knee joint.

Whilst the isolation of the quads is a benefit of the move, it is also related to how it damages your knees. Because the exercise only trains the quads, it fails to engage the hamstrings which usually support the knee by reducing the stretch of the anterior cruciate ligament in your knee.

That’s not to say that they definitely cause knee damage, like all exercises, the move will affect everyone differently – they can be bad for some people but fine for others.

Provided you have the right form, don’t overload the weight, and execute the movement correctly, leg extensions are fine and can even play a role in preventing injury by strengthening the joints in your knees.

The potential for damage to your knee can be kept to a minimum by sticking to low weights and higher reps.

You don’t need to avoid leg extensions altogether, just approach them with some common sense. If you experience pain, or if you have an existing ligament injury, steer clear of this exercise. Otherwise, give it a try! 

If you’re still apprehensive, keep reading for our leg extension alternatives that will work your quads with less knee strain. But first, check out these different leg extension exercises and variations.

Leg Extension Variations With A Machine

Try A Single Leg Extension

single leg extension image

To do a single leg extension, it’s pretty much the same as the regular movement but you only use one leg to move the weight. For all single-leg exercises, we recommend that you use your less dominant leg for your first set.

Just using one leg makes this variation of the exercise a form of unilateral training. The key benefit of unilateral training is that it makes it easier to work the muscles on both sides of your body equally.

Often, when you train both legs at the same time, the dominant side of your body will take on more of the stress and therefore work harder than the less dominate side.

By only training one leg at a time, you force the muscles on both sides of your body to work equally as hard, preventing muscle imbalance. Aside from appearance and strength, correcting muscle imbalance has further benefits for improving your balance and preventing injury.

Change Your Foot Position 

leg extension alternatives - different foot position image

The quads are made up of four muscles: The rectus femoris, the vastus lateralis, the vastus intermedius and the vastus medalis. Together, the quads make up the biggest muscle in your body.

As mentioned, leg extensions train the quads in isolation. With your feet facing forward, the machine works all your quad muscles pretty evenly. 

Thanks to this leg extension variation, you can target specific muscles in the quads. Whether there’s a specific area of your front thigh that you want to target, or you just like some variation in your workout, give this a try!

If you position your feet so that your toes face inwards, the vastus lateralis will be forced to work harder than the rest of the muscles in your thigh. Use this position if you want to target your outer thigh.

To target your muscles thigh in the rectus femoris and the vastus medialis, you’ll see better results if you position your feet so that your toes face outwards.

Leg Extension Without Machine

Below are our favourite solutions for you to do leg extensions without a machine.

Seated Bodyweight Leg Extensions

This variation is really accessible – all you need is a chair! And because this move uses bodyweight, it’s less stressful on your knees.

Sit on a chair with your back straight and put your feet on the floor hip-width apart. Extend one knee until your leg is extended and hold it for a second and then return to the start position. Repeat with the same leg for your first set, and then swap.

Chair Leg Extensions with Dumbbells 

Mastered the seated bodyweight leg extension?  Grab a dumbbell. 

To execute this move, grab a chair – one where your legs don’t touch the ground is best (we recommend stacking steps like in the video below).

Sit on the steps, making sure there is a 90°angle between your upper and lower leg. Place a dumbbell between your feet and hold it. Extend your knees until your legs are extended in front of you. Hold this position for one second and then move your legs back to the start position. Repeat.

Standing Leg Extension 

Try this variation for a move that will work more than just your quads. This move targets your core as well as your quads, and so has benefits for your balance and coordination, too. 

Start stood upright with your feet hip-width apart and your arms by your sides. Bend your knee and flex your hip to raise your thigh until it’s parallel with the floor. Straighten your knee to extend your leg out in front of you. Hold the position for a second and then slowly return to your starting position. Repeat the move with the same leg for one set and then do a set using your opposite leg. 

If you want to make this move a little harder, you can use resistance bands. Anchor a resistance band behind you and attach it to an ankle strap. Bend your knee and put the ankle strap on the ankle of your bent leg. Here’s how to execute the move:

If you want to try these resistance band variations at home, you can find our resistance band buying guide here.

Cable Leg Extension

If you’re a member of a gym, you can try a cable leg extension. 

Head over to the cable machine attach an ankle strap to a low pulley and then attach it to your ankle. Stand facing away from the pulley and hold on to the cable machine. The movement is the same as the standing leg extension, check out the video above to see exactly how to do this variation.


Kneeling Leg Extension

Sometimes called a natural leg extension, this move is another variation that only uses bodyweight.

To do a kneeling leg extension, start knelt on an exercise mat with your knees hip-distance apart. Your knees and your feet should be parallel. Put your arms reached out in front of you and start to lean backwards as far as you can. Make sure that you engage your core, glutes, and quads – this will help you keep your posture and reduce the risk of injury. Use your quads to move your torso back to the start position and then repeat the movement.

Lying Leg Extension

The lying leg extension is another great variation which. All you need is a bench and a resistance band.

Wrap a resistance band around the bottom of the bench and then attach the band to your ankle. Lie with your back on the bench and position one of your legs pointing up, so that it’s at a 90°angle to your torso. Bend that leg at the knee, so your lower leg is parallel to the floor. Hold this position for a second before straightening your leg back up. Repeat this move with the same leg for the first set, and then swap.

Leg Extension Alternatives

If you’re not quite convinced that the leg extensions benefits outweigh the risks, we get it, but that doesn’t mean your quads have to miss out. Check out these alternatives instead!


Lunges are a great leg extension alternative because they are an equally easy and accessible movement. Basically, the lunge is suitable for complete rookies and seasoned gym-goers alike.

For beginners, lunges are a great single-leg bodyweight exercise. As you get used to the move, there are plenty of variations that can keep this exercise challenging.

Forward Lunges

Lunges are a great way to exercise the knee extension and strengthen your quads. Lunges have a reduced strain on the joints in your knee because they exercise the flexion and extension of multiple joints, including those in your hips, ankle, and knee.

Regular lunges are really accessible because they’re a bodyweight exercise. With lunges, you can strengthen your quads literally anywhere without the need for any equipment or machinery.

How to do a lunge:

  • Stand upright, engage your core, and hold your hands at your hips.
  • Take a big step forward with one foot, this foot should be flat.
  • Shift your weight forward and lower your body so that your front thigh is parallel to the ground and directly above your ankle (this is what prevents knee strain!).
  • Both of your knees should be at a 90°angle, your back knee should be pointing towards the floor, with the heel of your back foot lifted away from the ground.
  • Push into your front foot to return to your original standing position.
  • Repeat this movement with the opposite leg.

Unlike the leg extensions, lunges don’t isolate your quad muscles. Nevertheless, they are still are a great exercise to strengthen your quads, with the added bonus of emphasising your glutes, too.

If you want to kick your lunges up a level, hold dumbbells (kettlebells work too) by your side as you do the movement.

Better yet, the barbell lunge and reverse lunge are slightly more intense leg extension alternatives. Keep reading for more detail on these!

Barbell Lunges

Adding resistance to your lunges with a barbell will help the move to build your quad muscles even more.

A barbell lunge is pretty similar to the regular lunge, but it’s best to start this move in a squat rack. Here’s what to do:

  • Set the bar on a rack just below your should level and load the bar with your chosen weight.
  • Step under the bar so that the barbell is in place across your upper back muscles.
  • Grab the bar with both arms and lift it off the rack by pushing through your legs.
  • Brace your core and keep your upper body straight.
  • Lunge!

Reverse Lunge

Compared with leg extensions (and basic lunges, too!) reverse lunges are easier on your knees without compromising the benefits for strengthening and toning your quads.

Check out this article from Stack for more benefits of reverse lunges compared to forward lunges.

Reverse lunges are great for developing your overall strength, as well as your balance, as they also activate the muscles in your core, your glutes, and your hamstrings. Here’s how to do this leg extension alternative:

  • Stand upright, engage your core, and hold your hands at your hips.
  • Take a big step back with one foot and then lower your front knee to a 90°angle, so that your front thigh is parallel to the ground.
  • Your front knee should be directly above your ankle.
  • Your back knee should be pointing towards the floor, also at a 90°angle, and the heel of your back foot should be lifted away from the ground.
  • Push into your back foot to return to your original standing position.
  • Repeat this movement with the opposite leg.

That’s one rep done!

If you’re a beginner, try 2 sets of 12 reps to start. If you think of yourself as more of a fitness fanatic, you can add dumbbells to this variation of the lunge too, or you can do the move from a deficit.

To do a deficit reverse lunge, start on a raised surface (a step platform is perfect) and then as you lunge, step off the platform with your back leg. This variation is slightly harder but safer for your knee joints.

If you want to push this move to the max, you can add bicep curls! Instead of just holding dumbbells by your side, curl the weight up as you’re pushing yourself back to the starting position.


Squats are another great exercise to replace leg extensions. Squats allow you to train your quads without as much risk of injury.

Squats are the ultimate lower body workout for strengthening your hamstrings, glutes, calves and core muscles. With the variations below, you’ll be able to make your squat target and tone your thighs.

Start with a standard bodyweight squat to perfect your form and then give some of these quad-targeting variations a try!

Cyclist Squat

Cyclist squats are also known as quad squats so it’s pretty self-explanatory that this move does wonders for increasing the strength and size of the quads.

Cyclists use this variation because strong quads are the secret to cycling success. That’s not to say this move is limited to bike lovers, it’s great for anyone who wants well-defined thighs (so, pretty much everyone).

How to do it:

  • Stand with your feet side by side, about 6 inches apart.
  • Place your heels on an elevated surface (a wedge board is best, but you can use a barbell plate to improvise).
  • Keep your upper body straight and squat down slowly, pushing your knees as far forward as possible.
  • Push yourself back up, but don’t lockout. This will make the move a little harder, but you’ll be grateful when you start to see the results.

Elevating the heels during this exercise allows the move to isolate your quads – the higher you elevate your heels, the harder the move will work your quads. Exercises that isolate the quads aren’t all too common, making this one of the most relevant leg extension alternatives!

Bulgarian Split Squat

The Bulgarian split squat is another squat variation which gives an intense quad workout. Bulgarian split squats are a single-leg exercise which works all of the muscles in your lower body. They’re not a quad isolation exercise like the cyclist squat, but they’re still a pretty good alternative to the leg extension for sculpting your thighs.

How to do a Bulgarian split squat:

  • First, you’ll need a bench or a step. Any platform that comes up to your knee in height will work.
  • Stand in front of the bench and get into the forward lunge position, resting the top of your back foot on the bench.
  • Lower your body until your thigh is almost parallel with the floor and your back leg is close to the ground (make sure your knee stays above your foot!).
  • Push yourself back up using the heel of your front foot.
  • Repeat the move on this leg around 8 times, and then switch legs.

To maximise the quad benefits of this exercise, try it with a barbell on your back or at a deficit like we explained for the reverse lunge.


Step-ups are a great leg extension alternative to train your joint extension, at home or the gym, with a lower risk of injury.

Step-ups are also a single-leg exercise, so they have similar benefits to single leg extensions for training both sides of your body equally. You can find these benefits of unilateral training above where we discussed single-leg leg extensions.

Try this basic step-up workout first:

  • Grab a step (or something similar).
  • Face the step and stand with your feet hip-width apart.
  • Put your left foot (or whichever is your less dominant leg) on top of the step.
  • Pushing your body up, pressing your foot into the top of the step and bring your right leg onto the step.
  • Step back with your right foot on to the floor, keeping your left foot on the step.
  • Repeat and then switch legs for the next set.

Isometric Leg Tuck

An isometric leg truck is another movement that is effective at exercising your thighs making it a suitable leg extension alternative. All you’ll need is a medicine ball and an exercise mat. Here’s how to do it:

  • Sit on an exercise mat with your legs stretched out in front of you.
  • Place a medicine ball on your lower legs.
  • Lie back on to the exercise mat.
  • To start the move, bend your legs until your thighs are perpendicular to the ground.
  • Hold your legs so that there is a 90°angle between your thighs and your lower legs.
  • Keep your lower legs in this position holding the medicine ball for as long as you can.
  • Return to the start position.

Leg Press

Ok, so you need a machine for this one too, but it’s still worth mentioning. I’m pretty certain that every gym has some kind of leg press machine, if yours doesn’t, switch gyms.

The leg press machine makes the move easier and safer for beginners compared to exercises that require free weights. Just like we said about leg extensions, using an exercise machine makes it easier to keep your form.

Leg press start position:

  • Sit on the machine with your head and your back resting against the back of the seat and your bum flat on the seat – keep this position throughout!
  • Place your feet flat on the plate, shoulder-width apart.
  • Your toes should be facing slightly outwards, and if you want to emphasise the quads (which of course you do, you’re here looking for leg extension alternatives), position your feet slightly lower down on the plate – but not so low that your knees are passed your toes.
  • You may need to adjust the seat position to make sure that your knees make a 90°.


  • Use your feet to push the plate away.
  • Slowly extend your legs.
  • Pause at the top of the move.
  • Slowly return the footplate without letting go of the weight.

Before you go!

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About the Author: Abbie Watkins

Abbie Watkins OriGym
Holding an MA Marketing Communications and Branding as well as a BSc Psychology from the University of Liverpool, Abbie’s experience encompasses the retail, hospitality and fitness industries. Since joining OriGym, she has become a qualified Personal Trainer and gone on to complete a specialist qualification in advanced Sports Nutrition. Abbie’s main focuses cover staying up to speed with YouTube fitness influencers, identifying successful and innovative content formats. She has contributed to various publications, including the Daily Express. Beyond OriGym, she enjoys going on scenic runs and upbeat exercise classes, and often found on the front row of a Saturday morning spin class. 

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