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February 11, 2022 8 min read

Squats are a compound exercise, so it works several muscle groups versus focusing on one particular area. This can be beneficial if building strength is your goal, but if you want to maximize your muscle growth, you’ll want to implement isolation exercises such as the leg extension.

Machines Versus Free Weights

With everyone fighting over the squat rack, it can be easy to forget about the machines in the gym. 

Although dumbbells and barbells may be seen as more superior than machines, using either consistently can offer similar results to strength and size

Machines can be beneficial for beginners because they can offer more of a fixed path, making form easier to maintain. They also allow for a proper range of motion, helping reduce the risk of an injury or an inefficient workout. Advanced lifters can also benefit from machines because they can provide more stability, which can help isolate the muscles being worked more. 


Isolation exercises can help induce muscle hypertrophy more than compound exercises, so using machines may be a better choice for bodybuilders or anyone looking to increase muscle size.

Leg extension in the simulator on quadriceps. 3D illustration

Muscles Worked by the Leg Extension 

The leg extension machine is designed to isolate the quadriceps by performing knee extension. This exercise can elicit higher quadricep activation, specifically during eccentric phase, compared to the leg press or traditional barbell exercises.

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. This muscle group helps in movements that involve straightening the knees like running, walking, standing, or movements of the legs across its various planes. They bear the weight of the body and need to be strengthened in order to have better agility and mobility for both functional and sporting activities.

These muscles originate from the attachment of the femur to the hip. Due to this connection, the rectus femoris also assists in the hip's flexion. 

Together, the quads make up one of the most significant muscles in the body. 

Leg extensions also help activate and strengthen the patellar ligament and quadriceps knee attachment. The leg extension exercise works based on torque force. Using a weight that rests close to your ankle joint, you push through your quads to straighten your knee.

Benefits of the Leg Extension

The primary benefit of leg extensions is their ability to isolate, target, and strengthen the quad muscles. Unlike other exercises like the square, leg extensions focus on the quad muscles and are a great way to bulk up on your thighs.

Strong quads are a great way to improve power output and athleticism. It strengthens the thighs, acting as a direct improvement in sports that require leg power like football, running, and cycling. 

  • Lower body strength: Stronger quads can provide better stability to the upper body and improved coordination. Although your quads can help improve lifts and overall gym performance, they also play an important role in function. Strengthening the quads with an exercise like the leg extension can help build lower body strength and improve daily function, which is especially important as we age.
  • Prevent injuries:The strengthening of the thigh muscles and their ligaments goes a long way in preventing and reducing the risks of injuries. Quadricep injuries are common especially in athletes and can often reoccur. Isolating a muscle to strengthen it can help further prevent the chance of injuries in athletic activities as well as daily life. 
  • Foundational exercise: In order to squat properly, you first need a solid foundation to perform the exercise and to continue progressive overload. The quadriceps play an important role in the squat, so being able to isolate them with the leg extension can be beneficial for building a better squat foundation. 
  • Beginner-friendly: Beginner lifters often tend to gravitate towards machines over free weights since there is a fixed pattern and range of motion to follow. Leg extensions are one of these machines and can be used by just about anyone at any fitness level. The machine itself provides more stability that may be needed for beginners, and it can be easily adjusted. 
  • Isolation exercise: Unlike compound exercises, isolation exercises target only one muscle group compared to multiple. This can help maximize hypertrophy and directly strengthen the muscles that may be overlooked during compound exercises. ADABOLIC recovery aid can help push you through the most strenuous of isolated and compound leg day exercises and can allow your muscles to recover quicker.  
  • Rehabilitation:Exercising after an injury requires patience and proper knowledge to help avoid reinjuring the area. The leg extension can be a great way to retrain your quads, knees, and the involved ligaments after an injury or surgery. Movement patterns of the knee extension can help rehab muscles and ligaments after surgery and can be a great way to get back on your feet along with the advice of a physician.  

Tips to Help You Through the Leg Extension

Despite being a simple exercise, common mistakes can ruin a good leg extension workout. This can limit the contraction of your muscles and the equivalent muscle response needed for excellent output. 

Here are some tips to help you avoid these common mistakes:

  1. Avoid lifting too heavy:While you might be tempted to lift more heavily than you can handle, you should remember that this could put a strain on your knee joint. Before you load up the machine to the max weight, begin with a weight you are comfortable with and work your way up. This can help ensure that you don’t strain your knee joint and end up with an injury.
  2. Don’t forget your calves and hamstrings:Although strengthening your quads is important, only focusing on a certain muscle group can lead to muscle imbalances. If your quads are stronger than your hamstrings, it can put you at a higher risk for injury. Pairing the leg extension with exercises like the leg curl and calf raises can be a great way to help avoid these imbalances. 
  3. Avoid slouching:A machine can help provide stability and proper form to individuals that may need it, but it doesn’t totally eliminate your need to maintain proper alignment. Especially when pushing heavy weight, your back may slouch as you try to lift your legs. It’s important to be conscious of your posture to help avoid back pain. 
  4. Match the machine rotation and your knees: Knee position is crucial during leg extension. Ensure that the rotation axis of your knees and that of the machine are in sync. This will help you get the most out of your extensions without risking an overexpression on your knees. Do not put your knees too far behind or in front of the axis rotation to avoid putting stress on your knees.
  5. Take time off to recover:As much as your body needs exercise, it also needs time to rebuild and heal the broken down muscle fibers. This is vital for proper muscle growth and function. Take time off between each workout and ensure that you get adequate sleep. RESTED-AF can help you get better sleep and improve muscle recovery. Better sleep helps achieve better muscle fiber recovery and cognitive function for better focus. 

How To Do The Leg Extensions

To get the most out of your leg extensions, you must perfect your form during this exercise. What form? You might ask, given that you need to locate the nearest leg extension machine and settle right in.

Like any other exercise, there are particular set rules you need to play by. These rules and tips would ensure that your form is perfect for the engagement of the necessary muscles.

To do the Leg Extension:

  • Sit in the chair of the leg extension machine.
  • Keep your back straight and against the backseat.
  • Grip the side handles on each side of the chair
  • Place your feet behind the padded roller so that your shins come in contact with it.
  • If the padded roller does not lie just above your shin, you might need to adjust the chair to the correct height.
  • Engage your core.
  • Inhale and lift the padded roller away from you by moving your legs forward and extending them.
  • Stretch your feet forward until they are straight.
  • Once your legs are fully extended, hold this position for about three seconds. 
  • Squeeze your quads for the best effect
  • Gently lower your legs, bringing the bar back to the starting position.
  • This is one repetition. Repeat for as many reps as you can fit in a set.

    Leg Extension variations: 

    1. Bodyweight Leg Extensions

    Bodyweight leg extensions can be great for firing up your quads and require no equipment other than your own body and gravity. It can be beneficial for muscle strength and for knee health. 

    To do Bodyweight Leg Extensions: 

    • Kneel on the floor.
    • Keep your back straight and your neck neutral.
    • Your knees should be at a 90-degree angle with the floor.
    • Pre-tension your knees and squeeze your quads.
    • Tighten your core. Your body should form one straight line from your head to your knees.
    • Keep your back straight, lean back until you reach your limit.
    • Hold this position for a second.
    • Without slouching or using your hands for support, return to the standing position by keeping all the tension in your thighs.
    • Complete as many repetitions as possible.

    2. Standing Leg Extensions


      Another beginner friendly exercise are standing leg extensions, and they can offer similar benefits as a machine, but you focus on one side at a time. This can help ensure each quad is worked equally and can improve bilateral exercises. 

      To do Standing Leg Extension: 

      • Attach a cable or a resistance band to a sturdy object.
      • Fix the other end around your right ankle.
      • Stand close to the sturdy object, leaving little to no tension in the band.
      • Stand with your feet hip-width apart.
      • Keep your back straight and arms straight beside you.
      • Contract your core and pull your shoulders back. Put your hands on your hip for better balance.
      • Exhale and lift your right foot off the floor without moving any other part of your body.
      • Extend your knee fully out until you reach my limit.
      • Inhale and slowly return your right leg to the starting position.
      • This is one rep. Complete as many reps as you can fit in a set.

      3. Banded Leg Extension

        Although resistance bands are commonly used as warm-up devices, they can also be substituted for machines or free weights. The banded leg extension may be able provide similar gains as the machine leg extension, which can make it a great variation that can be done anywhere. 

        To do Banded Leg Extensions: 

        • Wrap one end of the resistance band around a sturdy object behind a bench.
        • Sit on the bench and wrap the other end around your ankles.
        • In the absence of a sturdy anchor, wrap one end of the ban around the leg of a short bench and sit on the extreme end of the bench.
        • Keep your back straight and your knees at a 90-degree angle.
        • Grip the bench for support if necessary.
        • Slowly lift your feet off the floor, extending your knees.
        • Pause at the peak of the movement.
        • Slowly return your feet to the starting position.
        • This is one repetition. Complete as many reps as you can fit in a set.

        Stronger Quads for Stronger Legs

        Understanding the importance of the quads is crucial for building a stronger lower body. The leg extension eliminates the need for stabilizing or surrounding muscles to take over, so you can fully focus on one muscle group.

        We love big, compound lifts like the back squat, but implementing isolation exercises can help make those lifts even bigger and better. Whether you’re a beginner or advanced lifter, you can find a place for the leg extension in your workout.