Leg Extension Exercise | Technique & Common Mistakes

The Leg Extension is an exercise that will isolate the quadriceps and can be used towards the end of a workout as a ‘finisher’ or right at the very start as a ‘pre-exhaust’ method of training. This is a unique exercise due to its ability to solely isolate the quads.

Typically, all quadriceps isolation movements are the quad extension or a variation of it, such as; single-leg quad extension, cable quad extensions, partner-assisted quad extensions. This movement is a basic one meaning anyone can utilise it yet it can be so effective at the same time regardless of your training ability.  This is also a movement often used to strengthen the area when a knee injury has occurred.

Leg Extension Technique

Muscles Targeted

Unsurprisingly, the quadriceps contains 4 muscles, hence the ‘quad’;

  • The rectus femurs (The middle of the thigh and most predominant section)
  • The vastus lateralis (The outer side of the thigh muscle)
  • The vastus intermedius (The front top of the thigh)
  • The vastus medialis (The inner side of the thigh).

When combined together, the quadriceps muscle plays an extremely crucial role in knee joint flexion as well as hip flexion. Furthermore, the quadriceps contribute majorly to assist in everyday activities such as running, walking, skipping, and of course, those brutal leg sessions.

Machine Set-Up

  • Sit on the machine, with both legs positioned under the pad. To maintain stability and positioning throughout the movement, ensure that you are holding onto the bars on the side and that your feet are pointing forwards.
  • As you exhale your breath, extend your legs using only your quadriceps until they are fully extended. Throughout this part of the movement, the only muscle that should be under stress and tension is the quadriceps; keep the rest of the body as still as possible.
  • Once the quadriceps have been fully extended, hold for one second and squeeze the working muscle.
  • As you inhale your breath, lower the weight back to the starting position in a controlled movement.
  • Once the legs are back in the starting position once again, repeat for the number of repetitions required.

How to use the Leg Extension Machine

Benefits of leg extensions

Improves athletic performance

Improving the strength of your quads will improve your power output when running and jumping for example.  Stronger quads also support the glutes, back and knees.

Burns calories

As with any exercise, calories will be burned however, with this exercise targeting a group of four muscles, it will increase the rate of calories being burnt off ever so slightly.

Throughout these quadriceps sessions, it is important to combine muscle-building compound exercises along with a variety of isolation exercises. An isolation exercise is a resistance training exercise that will involve only one joint and very few muscle groups.

Whilst compound exercises such as squats, lunges, and leg presses are perhaps seen as the ‘go to’ quad exercises, the following article will depict the isolation exercise; The Quad Extension, along with its technique and some common mistakes that you can expect to see in the gym when performing it.

Common Mistakes

Creating stress at the knee joint

To prevent this, or at least minimise this, proper form is key. When positioning yourself in the starting position of a quad extension, the pad needs to be placed just on top of the lower leg and there needs to be a 90-degree angle between the upper and lower leg. Anything less than 90 degrees will result in the knee being positioned over the toes, which will result in undesired stress at the knee joint. Furthermore, anything more than 90 will cause less effective contractions at the quads.

Feet Positioning

The leg extension is an exercise solely for the quads, however, as mentioned earlier; there are four parts to the quads. The quad extension can target each individual part of the quad when the feet are positioned differently. As well as targeting each part of the quadricep separately, this can also be a great way to switch up your training and prevent it from becoming boring with the same variation of the quad extension every week. Positioning your feet inwards during the extension will target the vastus lateralis (outer thigh), whilst turning the toes out will target the vastus medialis (inner thigh) also.

Accepting Failure

Usually, when the strain sets in, that is the sign of the end of leg day. Instead of allowing this to happen, when the pain starts, that is when the session starts. If you feel like the pain is too much and you cannot do anymore repetitions on the leg extensions, add some rest-pause repetitions. This is where you work to the point of failure and physically cannot do anymore, pause and rest, then burst out a few more reps.

Not Keeping Adequate Intensity

All realms of training bear different rest periods. If looking to build maximal strength, rest between sets should be kept to 3-5 Minutes. For those looking to build power, look at a similar time frame also. However, if you are looking to build muscle/tone up then training should be kept to a minimal 30-90 Seconds. Leg sessions are commonly not intense enough; not due to lack of volume and effort but due to resting too much between sets.

Sticking to this rest time will optimise hypertrophy (muscle growth in size and strength), stimulate growth hormone, and also create a time-efficient workout! To prevent this from happening, try some of the following solutions; train with a partner who will time the rest periods, have a stopwatch, and stay focused.


Bodyweight Leg Extensions

  • Take a chair and sit with your feet planted, hip-width apart
  • Ensure your back is straight
  • Extend the knee forwards and tense the quad muscles
  • Return to the start position and repeat for required reps

Standing Leg Extensions

  • Stand with your feet hip-width apart
  • Engage the core and lift foot off the floor by 1 or 2 inches
  • Extend your lifted leg forward
  • Maintain balance by keeping your core engaged
  • Return and repeat for the desired number of reps


  • Stand with your feet shoulder-width apart. 
  • Engage your core and straighten your back. 
  • Push your hips back and bend your knees.
  • Lower your hips until your front thighs are parallel to the floor. 
  • Keep your knees above your ankles.
  • Push into your heels and stand up.

Bulgarian Split Squats

  • Stand with your back to the bench. 
  • Split your legs into a lunge stance, resting the top of your right foot on the bench. 
  • Plant your left foot on the floor.
  • Bend your left leg to lower your right knee. 
  • Lower yourself until your left thigh is parallel with the floor and your right knee almost touches the floor.
  • Push into your left foot and return to starting position.

Take Home Message

Whether it be to start your session and pre-exhaust the muscles or to finish off a big leg session, hitting the leg extension will benefit the quads in many ways and is a very useful exercise to add to your day!

Chris Appleton

Chris Appleton

Writer and expert

Chris is an editor and a level 3 qualified Personal Trainer, with a BA honours degree in Sports Coaching and Development, and a level 3 qualification in Sports Nutrition. He has experience providing fitness classes and programs for beginners and advanced levels of clients and sports athletes. Chris is also a qualified football coach, delivering high-level goalkeeping and fitness training at a semi-professional level, with nutritional advice to help maintain optimal performance. His experience in the sports and fitness industry spans 15 years and is continuously looking to improve. In his spare time, Chris likes to dedicate it to his family while training in the gym.