Many people don’t know the differences between the two main lower body exercises—leg extension and leg curl.
Both of these can be done on either a machine or free weights and work your hamstrings, quadriceps, and glutes (your butt), so which one do you choose?
This article provides information on both the leg extension and leg curl to help you choose which one is right for you, depending on your goals, level of fitness, equipment availability.
You probably already know that you can use both leg extension and leg curl machines to build the muscles in your lower legs, but did you know there are differences between the two?
If you want to know all the details of how to do these exercises correctly, you have come to the right place!
Keep reading to learn more about what makes each exercise unique, plus pros and cons for using them in your workout routine.
What Are Leg Extensions?
A leg extension machine is used to work your quadriceps, otherwise known as your thigh muscles.
Using a leg extension machine is a great way to isolate one group of muscles and it allows you to target any imbalances in strength or size that might exist in your legs.
These exercises can be performed using free weights or with an exercise machine.
If done properly, they can help develop strong thighs and even reduce knee pain caused by weak quads or inflexible hamstrings.
How To Do Leg Extensions?
There are two primary variations of leg extensions: sitting and standing. Both have their pros, but we’ll focus on sitting leg extensions.
To do a seated leg extension, follow these steps: Place your lower back against the bench with both feet secured under one end of the cable stack.
Lift with your quads to straighten your legs until they’re fully extended (knees unlocked).
Return to starting position by lowering your legs back down toward ankle height at a moderate pace (around five seconds).
A full set should be done in 10-12 repetitions. Variations include adding more weight or moving into single-leg extensions for greater range of motion; in that case, work each leg individually after completing one repetition of regular doubles with both legs together.
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Leg Extension Pros
The benefits of the leg extension are twofold.
First, it will help you strengthen your quads more than almost any other exercise.
The leg extension is primarily a quad-dominant movement that can work the quads with greater intensity than even the squat.
Second, because the leg extension is a weight-loaded movement (the same as the squat), it can be used to condition your body for heavier compound lifts like the squat or deadlift.
This is important for powerlifters, Olympic lifters, or anyone who wants to increase their general strength without overloading on a single movement (i.e., if you’re an athlete).
If that’s your goal, choose sets of 8 to 12 reps performed once per week at 80% of your 1RM.
Leg Extension Cons
The cons of leg extensions are, though it will isolate the quads to a certain extent, the exercise is not functional.
That is because the quadriceps never work in isolation during a squat or run, or when walking up stairs.
There’s always a certain amount of muscle activity by other muscles (glutes, hamstrings).
For that reason there’s no need to do a specific exercise for your quads (leg extensions) but rather it would be better to lift heavy weights in combination with compound movements.
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What Are Leg Curls?
The leg curl is a hamstrings exercise that focuses on three different hamstring muscles: semimembranosus, semitendinosus, and biceps femoris.
By isolating each muscle individually and then doing reps in succession, you’ll have a better chance of making your hamstrings grow.
How To Do Leg Curls?
Lay face down on a leg curl machine with your lower legs under the padding. Position your upper body so it is perpendicular to your lower body, looking down at your feet.
Reach back with both hands to grasp one of each bar of the machine.
Contract your hamstrings to extend your legs out straight, then return them to their starting position.
Repeat for reps or time as you wish.
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Leg Curl Pros
The Hamstring curl is a very effective exercise for targeting your hamstrings, particularly your biceps femoris.
This particular variation of leg curl targets both the long head of your biceps femoris as well as the short head of your semitendinosus in a way that few other exercises can achieve.
Even if you feel like you’ve been neglecting one or both parts of your hamstrings, it’s hard to go wrong with a hamstring curl.
It’s a less common exercise than its sister movement, leg extension but that means most people don’t do it and therefore it may feel relatively fresh in your routine compared to all those legs extensions you’ve probably done before!
Leg Curl Cons
While strengthening your hamstrings with a leg curl machine, you can end up overworking your lower back.
The nature of a hamstring curl is to have weight bearing down on you as you try to contract your hamstrings.
This exercise may not be effective for some people, but others will find it extremely beneficial.
Since it’s an isolation exercise, make sure that your core is engaged at all times so that you don’t overload other muscle groups that aren’t working.
If you do experience lower back pain from doing leg curls, stop immediately and stretch before starting again.
It’s possible to do too much of any exercise without proper form!
Did you know both exercises can be done with only tour body weight as resistance?
You can do with with a piece of equipment like the one below.
Are Leg Extensions And Leg Curls Necessary?
While some people think that exercises like leg extension machines or even leg curls are unnecessary, they actually have some value.
And it’s not just because those exercises feel good or make you feel strong in your legs; they’re actually important to help your lower body gain strength.
If you don’t regularly exercise your lower body muscles, they can become really weak – particularly if you aren’t using them every day.
This can leave you with bad posture, an increased risk of injury, and more problems in daily life (like walking upstairs without falling over!).
That being said, squats, lunges, and deadlifts are the 3 most important exercises you should be doing for your legs every week.
Everything should be seen as an accessory to those exercises.
Did you know you can do both of these exercises with resistance bands?
To find out more on the differences between weight training and resistance bands check out this post next!
Can Leg Extensions And Leg Curls Replace Squats?
Squats are a staple in most people’s exercise routines because they work more than just your legs.
Research shows that squatting engages more muscles—including your glutes, core, hamstrings, and quads—which means you’re burning more calories than you would with other lower-body exercises like leg extensions or leg curls.
Plus, performing squats properly can prevent back pain by strengthening your core and improving your posture.
The only thing to keep in mind is that squats aren’t an isolation exercise; you shouldn’t be using a weight so heavy that it prevents you from engaging your abdominal muscles and supporting your spine as you lift it up.
In addition to doing multiple sets of 10 to 12 reps, try doing one set of eight quick reps for maximum muscle engagement.
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Can Leg Extensions Build Mass?
In a word, no. Sure, they can make your quadriceps bigger (for all intents and purposes, that’s what’s going on), but you won’t be adding much to your total leg mass.
If you want larger legs, it’s best to focus on exercises that involve more than one muscle group—squats for quads and hamstrings, Romanian dead lifts for hamstrings (which will also work your glutes), lunges for quads and glutes, etc.
All of these moves involve multiple muscles working together to help you get stronger.
That doesn’t mean you should forget about doing single-joint exercises like leg extensions—if nothing else, single-joint movements are an excellent way to isolate individual body parts for increased time under tension and thus build better technique.
But as far as adding size goes, other options are better bets if it’s size above strength you’re after.
Do Leg Curls Build Mass?
Of course, both exercises can help you strengthen your quads, hamstrings, and glutes. But they don’t do it in exactly the same way.
The main difference is that leg curls focus more on your hamstrings (the muscles behind your thighs), while leg extensions put more of an emphasis on your quadriceps (muscles in front of your thighs).
So if toning up those hamstrings is what you’re after, then give leg curls a try.
If, however, you want to build muscle mass around your thighs—something that will improve their shape by increasing their size—then go with leg extensions instead.
Your goal here should be about 3 sets of 8-15 reps for each exercise at least twice a week.
As for when to use them, either one works just fine for strengthening any day at any time during your workout; it really depends on what else you have planned for that particular session.
What Is The Best Hamstring Exercise?
The hamstrings are found on the back of your upper leg.
This muscle group includes three separate muscles called semitendinosus, semimembranosus, and biceps femoris.
The hamstring group is responsible for extending your knees and flexing your hips.
There are many great hamstring exercises you can perform to strengthen these muscles including hamstring curl, seated leg curl, deadlifts, good mornings and lunges.
However, not all exercises target all three muscles in different ways.
For example, a seated leg curl targets your biceps femoris (back portion of your hamstring) but not much else while a lying leg curl targets both semitendinosus (the middle portion of your hamstring) as well as biceps femoris.
To decide which exercise is best for you, let’s take a look at each one individually.
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Hamstring Curls
This exercise primarily focuses on your biceps femoris and less so on your semitendinosus or semimembranosus.
You can do hamstring curls with an EZ-curl bar or dumbbells.
Lie face down, place your lower legs under a platform where there is some resistance then extend your ankles to move upward toward straightening out your legs completely.
While lifting up, keep your butt from rising off of the ground since that would cause your thighs to assist rather than just going up and down. Do 8 – 10 reps for 2 sets per day for 4 – 6 weeks.
Lying Leg Curls
This exercise mainly focuses on isolating your semitendinosus and very little assistance comes from your other hamstring muscles.
It’s difficult to isolate just one of these muscle groups due to them working together however it’s possible depending upon how you position yourself during execution.
A simple modification is to bend one knee while holding onto a weight plate with your arms outstretched, doing nothing more than using gravity as your resistance.
Doing just 1 set of 15 reps done slowly will help build lean and strong hamstrings without bulkiness.
Romanian Deadlifts
Also known as stiff-legged deadlifts, these use your glutes and hamstrings predominantly along with minor involvement by your lower back.
Be careful when performing them since they put a lot of stress on your knees over time due to bending forward.
If done correctly though like leaning against a wall slightly bent forward with back flat (don’t round spine) where its perpendicular to floor pulling towards wall without bending knees too much.
A slight stretch is felt in the hamstrings then returning upright helping maintain flat spine throughout entire movement, no additional weight beyond own bodyweight should be used unless desired for greater challenge later after initial training period. When training, aim for 3 sets of 10 to 15 reps performed once a week.
The Final Mop Up
So there we have it, both exercises are worth adding into your training.
But I stand by what I said earlier, as good as there exercises are, they should not come at the expense of compound exercises like squats, lunges and deadlifts.