Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (2023)

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (1)

While leg extensions and hamstring curls can both be used to strengthen and build your leg muscles, I would recommend emphasizing one over the other depending on your weaknesses.

So what is the difference between leg extensions and hamstrings?The leg extension isolates the muscles in the front of the leg (quadriceps), while the leg curl targets the muscles in the back of the leg (hamstrings). Leg extensions can improve your squats, while hamstrings can be used to improve your deadlifts.

In this article, I'll explain when it's appropriate to implement leg extensions or hamstrings. I'll also go over the basics of each exercise, the muscles used, and their pros and cons.

Leg extensions vs. hamstrings: an overview

Lower body movements such as squats, deadlifts, and leg presses generally involve, but do not isolate, the hamstrings and quadriceps. Incorporating isolation work for these specific muscles, such as leg extensions and curls, for example, can improve strength, increase muscle mass, and "bring out" lagging body parts.

leg extensions

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (2)

The leg extension is an isolation exercise that focuses on the quadriceps muscles.

This exercise involves a knee extension, which is a key movement involved in the squat, lunge, and sprint exercises.

However, the quads are often targeted along with the glutes, calves, and core stabilizers in compound exercises. Therefore, if you want to focus on your quadriceps, leg extensions become a key component of a successful program.


Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (3)

LosThe leg curl is an isolation exercise.focusing on the hamstrings.

This exercise involves a squat, which is the key to stabilizing the squat.Create Tension When Deadliftingand brake while driving.

The hamstrings can be dominated by the glutes, calves and core stabilizers in compound exercises, while the hamstrings are a great addition to your program if you want to focus on the hamstrings.

Leg extensions vs. hamstrings: pros and cons

Leg stretching benefits:

  • The leg extension isolates the quadriceps.Compound movements like the squat target the glutes, hamstrings, and erectors, which can take attention away from activating the quads. By isolating the knee extension action, the quadriceps can receive more attention and work, which has many strength and size benefits.
  • The leg extension can help strengthen the squat.The quadriceps is a big engine in the squat, by strengthening the quadriceps we can improve the squat exercise.
  • The leg extension can improve knee and quadriceps health.Healthy joints and muscles can stretch and contract as they move through a full range of motion. Leg extension runs through the full range of squat/extension motion, which is critical to knee health.
  • The leg extension does not put pressure on the back or hips.When we have a hip or knee injury, we often cannot do compound exercises like squats or deadlifts. However, we still need some kind of strengthening exercise, so the knee extension can be a useful exercise.
  • The leg extension can be performed for many repetitions without fatigue.Unlike compound exercises, leg extensions aren't very strenuous as an isolation exercise and are of little consequence if you incorporate them into your routine. Also, this exercise allows you to do high reps, exhaustion and high sets.

Disadvantages of leg stretching:

  • Leg extension usually requires a machine.You may not have access to a machine to load this exercise. Banded variations can provide similar, if not greater, benefits for improving knee extension and quadriceps strength.
  • The leg extension cannot be loaded with enough weight.By only focusing on a single joint, the knee extension exercise cannot be as taxing as a squat exercise, which is multi-joint and involves larger muscles like the glutes and erectors.
  • Leg extension can put more strain on the knee.Isolation exercises can place more stress on a single joint. In contrast, compound exercises allow you to support other joints and muscles, putting less stress on a single joint and muscle.

Leg curl benefits:

  • The tendon insulates the hamstrings.Although the hamstrings provide the main movement in exercises such as deadlifts and morning exercises, they are often dominated by other muscles such as the glutes and quadriceps. Leg curls focus on the knee flexion action, which pays more attention to the hamstring muscles, isolating them.
  • The hamstrings can help strengthen the deadlift.The hamstrings are the driving force behind the deadlift. By focusing on the hamstrings, we can improve the deadlift.
  • Hamstrings can improve hamstring flexibility.Hamstring flexibility is critical in exercises like squats and deadlifts. Hamstrings strengthen the hamstrings in different ranges of motion, which can directly improve our positioning in squats and deadlifts.
  • The hamstrings don't put pressure on your back or hips.While compound exercises like Good Morning and Deadlifts can put stress on the back and hips, we still need to strengthen the muscles involved. A hamstring curl can be used to strengthen the hamstrings while staying in an uncompromising position.
  • The hamstrings don't get tired because they are uniarticular.Similar to the leg extension, the hamstrings isolate a single joint movement from the squat, which has many benefits and low costs when added to a program. Because of this, we can implement pullouts, high reps, and drop sets for maximum hamstring fatigue.

Disadvantages of leg curls:

  • The tendon usually requires a machine.It often takes a leg curl machine to fully utilize this exercise. If you don't have access to a leg curl machine, leg curl variations can equally stress your hamstrings.
  • The hamstrings cannot be loaded too hard.Sometimes higher intensities are the key to achieving plateau breakthroughs. While this may be the case, the hamstrings are somewhat limited in their resilience. Time reps can compensate for this by creating a different kind of stress on the hamstrings.
  • Leg bending can put more stress on the knee.Like leg extension, hamstring flexion isolates the small, single-joint knee flexion action that can put a lot of strain on the knee.

Sometimes bending the legs can also cause calf cramps. If this happens to you, check out my article:4 reasons for calf cramps when doing leg curls.

(Video) The Most Unique Leg Extension & Leg Curl in the World!

Leg extensions vs. hamstrings: muscles worked

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (4)

The leg extension isolates the knee extension movement, which targets the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. While the leg curl isolates the squat movement targeting the gastrocnemius, soleus, biceps femoris, semitendinosus and semimembranosus muscles.

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (5)

Knee extension and leg flexion exercises involve a different movement of the knee, so they target a different set of muscles.

Leg Extension Exercises vs. Compounds: Activating the Quadriceps

If we are trying to target the front leg muscles most effectively, i.e. rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius, we need to compare muscle activation between different exercises.

a role ofFeldmann et al. (2008)compared rectus femoris (quadruple) activation between squats, deadlifts, lunges, step ups, and leg extensions.

So what did they find?

They found that the leg extension was more effective at targeting the quadriceps than other exercises. While the squat, lunge, and raise target the quads in a similar way.

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (6)

Conclusion: Compared to other resistance training activities, leg extension was more effective in isolating the rectus femoris (quadriceps).

Hamstrings vs. Compound Exercises: Activating the Hamstrings

During the leg curl exercise, the semitendinosus, semimembranosus and biceps femoris muscles are mainly trained.

So how well do hamstrings work with your other exercises to work your hamstrings?

a role ofMcAllister et al. (2014), compared the hamstrings to RDL, Good Morning and Glute Ham Rise.

Surprisingly, they found that several hamstrings were more focused during the glute and RDL raises.

(Video) Are Leg Extensions Bad For Your Knees? | Do They Build BIGGER QUADS?

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (7)

So if your goal is to isolate and target your hamstrings, it's probably best to prioritize RDL and glute raises in your exercise selection.

However, hamstring curls remain a valuable exercise as they place minimal stress on key areas as it is a non-fatiguing single joint exercise. It is also less complicated to learn compared to the RDL and the butt lift.

Related article:The 12 best buttock augmentation alternatives.

Conclusions: Compared to the RDL and the glute and hamstring raises, the leg curl was less effective in targeting the hamstrings, but it remains a valuable non-fatigue single-joint exercise in targeting the hamstrings.

is that youHamstrings hurt more after deadlifts, you will wonder whether it is good or bad. Check out my article that explains more!

I go into more detail about butt lifts in my articleGlute Ham Raise vs Nordic Curl: Differences, Pros and Cons

Hamstring Leg Extensions: How to Do Them

How do you do the leg extension?

  • Position the back pad so your knees are bent over the front of the seat.
  • Position the leg pad so that it is just above your foot throughout the exercise.
  • Sit upright on the leg extension machine, keeping your spine neutral.
  • Grab the handles on the side of the machine for stability at all times.
  • Place your feet firmly under the pad with your toes pointing upwards.
  • From here, just straighten your legs until your knees are closed.
  • To complete the repetition, bend your knees back to the starting position.

How do you make leg curls?

  • Adjust the back pad a little further forward so that there is room between your knees and the seat.
  • Adjust the leg pad so it is just behind the ankle.
  • Sit upright on the leg curl machine, keeping your spine neutral.
  • Hold the sling just above the bottom of your legs so that it locks into the machine.
  • Grasp the handles on top of the machine for stability at all times.
  • From here, just step your heels back until your knees are fully bent.
  • To complete the repetition,Bring load back to knee extension.

Which exercise is best for you?

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (8)

While leg extensions and leg curls are great additions to an exercise routine, you can layer them depending on key variables.

When should the leg extension be used?

  • If you are in oneout of seasonfor Olympic training or weightlifting and want additional quad accessories.
  • You cannot crouch orThe Hack Squat Variationbecause of injury
  • You want to maximize the growth of your quadriceps.
  • You want to isolate the quadriceps as much as possible, as they are a lagging body part.

When to use hamstrings

  • Due to an injury, he is unable to perform Romanian Deadlifts or Good Morning Variations.
  • You want to improve your hamstring flexibility.
  • You want to improve knee joint mobility.
  • You want to maximize the growth of your hamstrings.
  • You want to isolate the hamstrings as much as possible, as they are a lagging body part.

When to use both

  • You want to improve overall knee mobility.
  • You want to strengthen your hamstrings and quadriceps, especially if you're a beginner.
  • You have extra time to train in the gym.

Recovering from an Injury: Leg Extension vs Leg Curl

Leg extension: the rehabilitation process

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (9)

After a back, hip or knee injury, we are often no longer able to do the exercises we could before. A simple question I am often asked is "What can I do?"

The knee extension is the simplest action that directly targets the quadriceps muscles. For this reason, several goals must be scored in recovery from injury:

  • Restore freedom of movement in the knee.
  • Strengthen and maintain the quadriceps muscles.
  • Improve flexibility in the quadriceps muscles.

To further disrupt this movement, you should be able to do seated leg extensions without weights. If you can pull it off, you can move on to banded knee extensions.

Leg extensions with bandsYou can do this by sitting on a box with your back facing an anchor point. From this point, wrap the band around your ankle and straighten your knee.

(Video) Leg Extensions: Good Or Bad? (Safe For Your Knees?)

To put more stress on the knee extensions, continue with a leg extension machine.

If you can't do a full-range knee extension, you can do a part-range leg extension to slowly work up to greater ranges of motion.

Hamstrings: the rehabilitation process

The hamstrings are responsible for knee flexion or knee stabilization, assisting the rest of the muscles during the bottom of a squat, or braking forces when cutting in speed drills.

Therefore, strong hamstrings are necessary but often overlooked when it comes to isolation work. For this reason, injury recovery should have several objectives:

  • Restore freedom of movement in the knee.
  • Strengthens the stability of the thigh muscles.
  • Improve flexibility in the hamstring muscles.

To further break this move down, you need to do slanted leg curls with just your body weight. Press this activity to improve range of motion when bending your knees.

That said, it's okay to experience discomfort with this exercise as long as there's no sharp pain. Focus on developing range of motion and flexibility in the hamstring muscles.

To progress, you can anchor a band to a shelf or rail and loop it around your ankle. This can be done lying down or standing with your back to the anchor point.

Finally, to put more stress on your hamstrings, you can use a leg curl machine.

Do you experience knee pain when squatting?see this article!

common questions

Here are some frequently asked questions about leg extensions and hamstrings:

Are Leg Extensions Bad for Your Knees?

While leg extensions are generally completely safe and effective exercises, they can put a strain on your knees. If you are experiencing discomfort, you would benefit most from a lunge, squat or glute bridge.

(Video) The TRUTH About Leg Extensions (BASED ON BIOMECHANICS!)

Are leg extensions better than squats?

While there's no substitute for adding a squat exercise to a program, the leg extension can hit the quadriceps more. For this reason, the leg extension is a valuable adjunct exercise to the squat movement.

Are hamstrings a waste of time?

The leg curl can be a valuable isolation exercise for your hamstrings. However, the hamstring is not a replacement for deadlifts or RDL exercises, but it can complement these compound exercises very well.

Lower body training guides

Check out our other lower body training guides:

  • How do weightlifters train their legs? (3 weight lifting exercises for legs)
  • Do powerlifters do isolation exercises? (It is yes)
  • 18 exercises to improve deadlift strength (with scientific backing)
  • Do hamstrings help with deadlifts? It is yes
  • The 7 Best Leg Exercises That Don't Use Your Ankles

Other exercise comparisons

  • Kettlebell Swing vs Deadlift: Differences, Pros, Cons
  • Bulgarian split squat vs lunge: differences, pros and cons
  • Back extension x glute lift: differences, pros and cons

final thoughts

Whether you're recovering from an injury or looking to isolate your leg muscles, leg flexion and extension exercises are great additions to a program.

While the leg extension was shown to be more effective at isolating the quadriceps, the leg curl seemed less effective at targeting the hamstrings than the RDL and glute hamstring raises.

For this reason, you can prioritize leg extensions to target the quads while prioritizing the glutes and hamstrings and RDL raises to target the hamstrings. However, the leg curl remains valuable for its non-fatiguing properties and single-joint nature.


Ebben WP, Feldmann CR, Dayne A, Mitsche D, Alexander P, Knetzger KJ. Muscle activation during resistance training of lower limbs. Int J Sports Med. 2009 Jan;30(1):1-8. doi: 10.1055/s-2008-1038785. Epub October 30, 2008. PMID: 18975260.

McAllister MJ, Hammond KG, Schilling BK, Ferreria LC, Reed JP, Weiss LW. Muscle activation during various hamstring exercises. J Resistance Cond Res. June 2014; 28(6):1573-80. doi: 10.1519/JSC.00000000000000302. PMID: 24149748.

About the author

Leg Extensions vs Leg Curls: Differences, Pros & Cons | powerliftingtechnique.com (10)

Javad Bakhshinejad was born and raised in the Washington area. He is currently a student at the University of Seattle, where he is pursuing a master's degree in kinesiology and was a former strength coach in the athletic department. He was a competitive bodybuilder for 8 years where he later switched to competitive powerlifting for 4 years. He currently has his own personal training business, working with powerlifters and bodybuilders.


Is leg curl or leg extension better? ›

Leg extensions and leg curls, also called hamstring curls, both work muscle groups in your lower body, but they focus on completely different ligaments and muscles in your legs. While leg extensions activate the quadriceps muscles on the fronts of your legs, hamstring curls target the muscles on the backs of your legs.

Is there any benefit to leg extensions? ›

The leg extension, or knee extension, is a type of strength training exercise. It's an excellent move for strengthening your quadriceps, which are in the front of your upper legs.

What are the benefits of leg curls? ›

What Are the Benefits of Leg Curl?
  • It activates the butt, thigh, and front shin muscles effectively.
  • Leg curls target both hamstrings and calf muscles, thereby making you strong and flexible.
  • It improves your overall strength, stamina, and balance.
Jul 1, 2022

Do leg extensions make your legs bigger? ›

Leg extensions were found to provide superior muscle growth in the rectus femoris compared to squat training. Vastus lateralis tended to grow more in the distal parts (25% and 50% of femur length) from squat training but grew more proximally (75% of femur length) from leg extensions.

Do leg extensions make your knees stronger? ›

Leg extensions are a key exercise in strengthening the patellar ligament and quadriceps attachment for the knee. This exercise focuses on strengthening the quad alone and, therefore, strengthens key attachments for the knee joint at the same time.

Do leg extensions hurt your knees? ›

Leg extensions are infamous for causing knee injuries. Because weight is placed on the ankles, the knee experiences a great deal of added force as it extends, which increases the likelihood of a patella or quadriceps tendon injury.

Should I do leg extensions or squats? ›

The bottom line is that squats don't work your rectus femoris. They will work your vastus lateralis (the sweep) at the middle and towards your knee, but not up towards your hip. For optimal rectus femoris development, and vastus lateralis growth towards the hip, opt for leg extensions.

What can I do instead of leg extensions? ›

  • Reverse Lunges.
  • Step Ups.
  • Lateral Step Ups.
  • Front Foot Elevated Split Squat.
  • Bulgarian Split Squat.
  • Elevated Heel Goblet Squat (Narrow Stance)
  • Narrow Stance Leg Press.
Feb 3, 2022

Do leg curls strengthen knees? ›

One of the most important muscle groups that need to get stronger to keep your knees fit and healthy are your Hamstring Muscles. This double-legged Leg Curl Exercise is great exercise to strengthen your knees and Hamstrings.

Do leg curls make your legs bigger? ›

But there is another muscle that assists the leg-bending motion, and it's known as the gastrocnemius -- the largest muscle of your calves. If you do seated leg curls on a regular basis, then you can get bigger calves.

Do leg curls increase testosterone? ›

Leg workouts can stimulate the release of large amounts of hormones. Working your legs helps to produce hormones such as cortisol, testosterone, and human growth hormone (HGH).

Are leg extensions a waste of time? ›

The Leg Extension Machine

Why it's a waste: “The stated goal of this machine is to strengthen your quads, but you actually end up just putting a lot of stress on your knees as you straighten your legs from the seated position,” explains Justice. What to do instead: A basic squat or lunge.

Are leg extensions harmful? ›

Based on this information, we can confidently debunk the myth that leg extensions are bad because they place too much stress on your knees. In fact, they may even place less stress on your patellofemoral joint at comparable loads or efforts than leg presses and squats.

How many times a week should I do leg extensions? ›

Your body needs the time to rest, meaning five days of leg training would actually be a counterproductive exercise, so stick to three days with recovery in between sessions.

How to do leg extensions without hurting knees? ›

When doing leg extensions to strengthen your quadriceps, your therapist may tell you to start in the seated position and only straighten your leg halfway (90°–45°). Restricting motion in these exercises can help minimize the pain while doing them.

Are leg extensions good for arthritic knees? ›

Strengthening the muscles around the knee is important for overall knee joint health. Leg extension and leg curl exercises are generally effective exercises for strengthening the quadriceps and hamstring muscles.

Are leg curls worth doing? ›

What Are the Benefits of Doing Leg Curls? Leg curls primarily isolate your hamstrings, working to strengthen the muscles and improve flexibility. Strong, flexible hamstrings will positively affect your body's overall: Strength.

Should I skip leg extension? ›

Leg extensions aren't for everyone. If you've healthy knees and a well-balanced training plan they can be a useful addition to your workouts if you're looking to build maximum quadriceps size. They're a good supplement to your multi-joint lifts and relatively easy to recover from.

Does leg curl make glutes bigger? ›

The muscles that make up your butt -- gluteus maximus, gluteus minimus and gluteus medius -- are involved in controlling stability and movement at the hip joint. Therefore, during most types of leg curls, the butt muscles are not recruited and therefore won't increase in size.

Are leg extensions safe? ›

Based on this information, we can confidently debunk the myth that leg extensions are bad because they place too much stress on your knees. In fact, they may even place less stress on your patellofemoral joint at comparable loads or efforts than leg presses and squats.

Is seated leg curl better than lying? ›

Conclusion: Hamstrings muscle size can be more effectively increased by seated than prone leg curl training, suggesting that training at long muscle lengths promotes muscle hypertrophy, but both are similarly effective in reducing susceptibility to muscle damage.

Are leg curls safe for knees? ›

Remember, the best way to strengthen your joints and be more resistant to injury is to strengthen the muscles surrounding the joints. Increased strength leads to improved function and a decrease in pain. The Leg Curl exercise is a vital one for overall knee health.

Should I do leg curls and extensions? ›

As such, supersetting or even simply programming the leg extension and the leg curl together in a workout is far more advisable than simply choosing one exercise over the other; thereby providing a more well-rounded and effective leg workout than what only a single one of the two exercises can achieve.

Do leg extensions make your thighs smaller? ›

The leg extension is a must for toning your thighs and it's an easy exercise for beginners. But adding weight makes it plenty challenging even for body builders, ACE says. This exercise tones your quadriceps (“quads”), the muscles at the front of your thighs.

Do leg curls build your calves? ›

Leg curls target the hamstrings (biceps femoris, semitendinosus, and semimembranosus) and calf muscles (gastrocnemius and soleus muscles). When lowering your feet back down, your buttocks (gluteus muscles), thighs (quadriceps), and front of the shins (tibialis anterior) are activated too.

Are leg extensions as good as squats? ›

The bottom line is that squats don't work your rectus femoris. They will work your vastus lateralis (the sweep) at the middle and towards your knee, but not up towards your hip. For optimal rectus femoris development, and vastus lateralis growth towards the hip, opt for leg extensions.

How many sets of leg extensions should I do? ›

Leg extensions tend to work best here. It's up to you how many sets you do/need; however, 5 is usually a good amount. Start the first set off lightly, maybe 60% of your working weight for 10-12 reps. Increase this to 70% for the second set, 80% for the third, 90% for the fourth and 100% for the 5th.

How many times should I train legs to grow glutes? ›

How often should you train the glutes for maximum results? The short answer is 2-6 times per week.

What do leg extensions target? ›

The primary muscle worked by the leg extension are the quadriceps. The quads or quadriceps femoris muscle is divided into four parts or muscle groups named the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.


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