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Leg Extension vs Squats: The Difference

Zachary Keith, BSc CSCS CISSN

When it comes to training your quadriceps, there are two basic types of movements you can use.

  1. Exercises involving movement around the knee AND the hip (squats, leg press, lunge, etc.)

  2. Exercises involving movement around the knee alone (leg extension, reverse nordic, sissy squat, etc.)

The truth is, there is a key difference between these types of exercises you need to know about if you want to completely train your quadriceps.


So, in this article I’ll explain why that is and how you can take action on it.

Example videos are provided at the end of the article.

If you have any questions left unanswered, feel free to email me at info@fitnesssimplified.org or comment below.


Super-Quick Quadriceps Anatomy

To start, let’s go over some basic anatomy of the quads. As you may know, there are four different muscles that make up this muscle group:

1)    Vastus lateralis

2)    Vastus indermedius

3)    Vastus medialis

4)    Rectus Femoris


There’s one only one key thing you need to know about these muscles.

The vasti muscles only cross the knee.

The rectus femoris crosses the hip AND the knee joint.

 

Why is this important?

For a muscle to exert any force, it must shorten (contract).

Because the rectus femoris crosses the knee AND the hip joint, it is unable to sufficiently contract during squat-like movements.

Think of it this way:

As you are standing up from the bottom of a squat, the recuts femoris shortens near the knee but lengthens near the hip.

As a result, there is little net change in muscle length; and therefore little contribution from the rectus femoris.

 

This has been shown in the research: the rectus femoris is much less active in squat patterns (squats/lunges/leg press) than the three vasti muscles [3,4,5].

The rectus femoris seems to be majorly involved in movements where only leg extension is involved. Also, because the rectus femoris crosses the hip joint, it will contribute to hip flexion to some degree.

  • hip flexion = your knee gets closer to your chest (opposite of what your glutes do)

 

Practical Applications

Based on what we just discussed, in order to completely train your quadriceps:

You need some squat-like movement (squat, leg press, hack squat, lunge),

and a knee-only movement (leg extension, reverse nordic, sissy squat).

 

As a general rule of thumb, there are three different quadricep exercises I’d recommend you include in a program or training block:

  1. Squat pattern

    • Squat, leg press, hack squat, etc.

  2. Knee only movement

    • Leg extension, reverse nordic, sissy squat, etc.

  3. Single leg movement

    • Lunge, Bulgarian split squat, etc.

Example videos

To conclude, I wanted to provide some example videos of my favorite knee-only quadricep movements.

You will find three exercises in the following order:

  1. Leg extension

  2. Reverse Nordics

  3. Sissy Squats

These exercises are also listed in order of their relative difficulty:

References

  1. Muscle Activation Patterns During Different Squat Techniques

  2. Effects of squat training with different depths on lower limb muscle volumes

  3. Changes in exercises are more effective than in loading schemes to improve muscle strength

  4. Effects of squat training with different depths on lower limb muscle volumes

  5. Inhomogeneous architectural changes of the quadriceps femoris induced by resistance training

  6. Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths

  7. Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position