How to Build Your Quads with Seated Leg Extensions — CPT Approved

The last few years, everyone's been cuckoo bananas for building their glutes. And no shame to the game, I too am chasing the backside gains. However, don't leave your quadriceps in the dust as you chase posterior chain glory. These anterior muscles help stabilize your kneecap and support running, squatting, and even jumping higher.

The leg extension machine is a classic in most commercial gyms, and this seemingly simple exercise — a seated position where you extend your legs out to lift weight — provides some serious muscle isolation for the quads. There's also the Leg Curl/Leg Extension Bench Attachment, which allows you to tackle this exercise from your own home gym.

How to Do Leg Extensions with Proper Form

Here's how to set up your typical seated leg extension machine to tackle leg extensions with perfect form:

• Select your weight either on the weight stack, by loading plates, or however resistance is adjusted on your machine — additional options utilize a cable machine or bands for resistance.
• Adjust the back rest forward or back so that when you're seated, your knees are aligned with the pivot point of the leg extension machine.
• Take a seat and adjust the shin pad so it's in contact with your lower shin, just above the ankle.
• Inhale and extend your legs to lift the weight.
• Exhale as you lower the weight back to start.

Pro Tip: When setting up, your hips (upper legs and torso) and knees (upper and lower legs) should form 90-degree angles.

Leg Extension Muscles Worked and Benefits

The leg extension on machine is an isolation exercise, solely targeting the quadriceps. However, the quadriceps are made up of four muscles that work together to extend the leg. The quad muscles are:

• Rectus Femoris: Located in the middle front of the thigh, it assists in straightening the leg at the knee. Also, this is the only quadricep muscle that helps to lift the thigh towards the body for hip flexion.
• Vastus Lateralis: Found on the outer side of the thigh, this is the largest muscle in the quadriceps. It assists with straightening the leg at the knee and works with the vastus medialis to keep your kneecap aligned and stable.
• Vastus Medialis: Located on the inner side of the thigh, this muscle helps straighten the leg at the knee and works with the vastus lateralis to keep your kneecap aligned and stable.
• Vastus Intermedius: This muscle sits between the vastus lateralis and vastus medialis, and underneath the rectus femoris making it the deepest quad muscle. It assists with straightening the leg at the knee and also supports knee stability.

Benefits of Bulletproof Quads

So, what are leg extensions good for? Strengthing your quadriceps via leg extension on machine or with a substitute (we'll detail some alternatives below) can build strength, size, and power — supporting stronger compound lifts like squats and deadlifts as well as assisting athletics that require explosive cuts, sprints, or jumps.

"The quadriceps ability to decelerate against forces created in sport movements is what keeps athletes on the court playing," says strength coach Dan Berman, NSCA, CSCS. "Having strong quads is incredibly crucial for athletes and knee health."

While knee pain can be tricky to understand — and it's always best to consult with a doctor or PT to help figure out how to treat it — building strong and more risilient quadriceps can help reduce (and prevent) knee pain and injuries since they're the muscles leading the charge in supporting the stability of your knee joint.

Leg Extension at Home Alternatives

While you may have the room for a dedicated leg extension machine in your home gym, those of us with limited floorplans may opt for more multi-functional equipment like a power rack, barbells, or even a GHD when space is limited. Here are some options to tackle leg extensions without machine.

Leg Extension with Kettlebell

Equipment Needed: A bench (box, or chair) and a kettlebell.

How To Leg Extension with Kettlebell: Sit on the edge of a box or chair, with your knee aligned with the lip's edge. Maintain a tall posture with your core engaged as you hook a kettlebell with a flexed foot. For this single leg extension, extend your knee and engage your quad to lift the kettlebell until your leg straightens out in front of you while the other leg remains planted on the floor. Then, lower with control. Finish your reps on one side then switch to the other.

Pro Tip:To increase the range of motion, take an adjustable bench and set the incline slightly above parallel — around 15- to 30-degrees. Sit on the end of the highest edge of the bench with your knee aligned with the very end. Then, tackle this one legged move while gripping the side of the bench to keep you locked in.

Dumbbell Leg Extension

Equipment Needed: A bench (box, or chair) and a dumbbell.

How To Dumbbell Leg Extensions: Similar to the leg extension with kettlebell, however this variation works both legs at the same time. Sit on a bench or box with your knee aligned with the edge. Hold onto the back or side of your seat for stability and grip a  dumbbell between both feet. Breath in as you extend your knees and lift the weight away from the ground, then exhale as you lower back to start.

Banded Leg Extensions         

Equipment Needed: A bench (box or chair), fixed object, and resistance band.

How To Banded Leg Extensions: Wrap a resistance band around a fixed object — a squat rack, fence post, something immovable. Take a seat in a chair and slip both feet into the resistance band loop, allowing the band to rest on your shins. Maintain a tall posture and grip the chair as you extend your knees, then flex your knees to return to start.

Pro Tip: If you want to increase the tension in the bottom range of this movement, try scooting your chair further away from where the band is wrapped to the fixed object.

Standing Leg Extension

Equipment Needed: An ankle cuff and cable machine.

How To Standing Leg Extension: Adjust the cable machine to about hip height and attach an ankle cuff to one ankle. Clip your ankle cuff to the cable machine and take 2 big steps away. If possible, place a hand on a doorframe, pole, or chair for stability as you flex your knee, sending your heel back and up. Then engage your quad as you extend your knee back to start.

Leg Extension Workout

This workout starts with a multi-joint compound lift that primarily targets the quads and glutes — best tackled when you're fresh. Followed by an RDL to bring your hamstrings in on the fun. And then finish everything off with a superset of leg extension leg curl exercises, isolating your quads and hamstrings while elevating your heart rate.

Rest for 60 seconds between sets.

• Back Squat 3 sets, 8-12 reps
• RDL 3 sets, 8-12 reps

Superset - Complete both moves back to back then rest for 60 seconds.

• Leg Extensions 3 sets 8-12 reps
• Leg Curls 3 sets 8-12 reps

Pro Tip: If you experience knee pain when performing leg extensions, you may want to opt out of this specific exercise or try a 30-45 second isometric leg extension hold instead. This replacement, which can strengthen tendons, helps to manage jumper's knee by reducing joint stress and irritation.

[Read More: 18 Alternatives When You Don't Want To Back Squat]

Takeaway

Toss on some seated leg extension reps to finish off your leg day, giving your quads some dedicated isolation work to help with deceleration in sport and added stability for your knees. Even if you don't have a dedicated leg extension machine, this quad focused work can be tackled in your home gym with a weight bench or box and a little creativity.

FAQs

Are leg extensions bad for knees?

When leg extensions are done with correct technique and the utiized resistance is within your ability — meaning, you're not having to break form to force the weight up — this move can be safe and effective for building leg strength. 

Is there a way to alleviate stress on knees?

Yes! Instead of using a rep range which can stress your knees with the repetitive movement, try an isometric hold where your quads remain engaged the entire time. Beginners can start out holding their legs extended for 10 to 30 seconds, and more experienced lifters can aim for 30 to 60 seconds. This can help build endurance and strength while limiting discomfort. Similarly, w

What do leg extensions work?

An ext. leg machine isolates your quadriceps, the muscle that makes up your thigh, right above you knees and below your hips on the anterior (front) side of your body.

What's the difference between leg extension vs leg curl?

While these moves look similar, and they're both isolation exercises, they target opposite sides of the body. The leg extension targets your quadriceps on the anterior side, while a leg curl targets the hamstrings on the posterior side. 

Rosie Borchert is a NASM-CPT, former Nike Volleyball coach, and fitness writer whose work has appeared on BarBend and Tonal. If anyone would like to hire her to play beach volleyball, snowboard, binge watch TV, or go climbing, please get in touch.

This article was reviewed by Ashley Boyer, ACE-CPT, for accuracy.