Squats, Quadriceps, & Inadequacies

Number of Scientific Sources: 12

Comprehension Level: Intermediate

Table of Contents

• “The Squat is King”: Giving Credit Where it is Due
• Anatomical Overview of the Quadriceps
• Biomechanical Analysis of the Squat: The Hip, Knee, & Quadriceps
• When Hypertrophy Research Confirms Kinesiology Concepts

“The Squat is King”: Giving Credit Where it is Due

The squat is often regarded to be the king of all exercises. Although this belief is up for debate, this debate is only limited to a handful of other exercises (i.e. the deadlift and the Olympic lifts) and not the point of this article. It is also only one of a few of exercises that allows a single soul to move 1,000+ lbs, if they can muster the strength (not many people have this ability).

The squat is one of the “best bang for your buck” exercises out there, since it can impose a high mechanical stimulus over a large mass of musculature. It will challenge much of your back, your core, and the majority of your leg muscles, making it an efficient exercise choice to get bigger and stronger. It is very difficult for me to think of a context where an able-bodied specimen would not benefit from some form of squatting in their training program.

Nevertheless, the squat surely has some deficits, some more known than others. Despite popular belief, the squat does not sufficiently train all four of the primary quadricep muscles. Hence the birth of this article.

Anatomical Overview of the Quadriceps

Important notes:

• The vastus intermedius is located behind the rectus femoris (RF), making it virtually invisible for aesthetic purposes.
• The RF is a biarticular muscle, meaning it crosses two joints (the hip and the knee). This has implications for movements where hip flexion and knee flexion (or knee extension and hip extension) occur at the same time (i.e. the squat).

Biomechanical Analysis of the Squat: The Hip, Knee, & Quadriceps

Alright, this paragraph may be a review for many of you, so bear with me. There are two primary joints that move during the squat: the hips and the knees (the ankles move too, but we don’t care about the ankles for the purpose of this article). The squat starts with the lifter standing upright. As the lifter descends, the hips go through flexion, in addition to the knees. The descent is followed by the ascent back to the starting position, which is characterized by hip and knee extension.

Recall that the three vastus muscles (v. lateralis, v. medialis, v. intermedius) originate on the upper parts of the femur and insert on the patella (AKA the knee cap) and the upper part of the tibia (AKA the upper shin). Since these muscles are monoarticular (AKA they cross one joint), they are unaffected by what is happening at a different joint, such as the hip. In other words, regardless of if the hips are going through flexion or extension, the three vastus muscles can produce force or experience tension while they shorten or lengthen during the squat. The three vastus muscles experience eccentric contraction during the descent and concentric contraction during the ascent.

The same cannot be said about the RF during the squat. When the hips are flexed to a certain degree, the RF cannot contribute to knee extension (11). Remember that this muscle crosses two joints, the hip and the knee. As a lifter descends during the squat, the RF does not experience a meaningful change of length or tension. This is because as the knee goes through flexion, the RF is pulled downward (because it inserts on the tibia), but the length remains relatively constant due to the fact that the hip is also going through flexion, so the angle is decreasing at this joint, too. On the flip side, as the knee and hip go through extension during the ascent (the force at the hip being produced by the gluteus maximus), the RF is pulled upward (because it originates on the pelvis). Lastly, recall that the RF produces hip flexion. Producing hip flexion would counter the ascent of the squat because the hip must go through extension to complete the movement. For good reason, the RF experiences little-to-no activation during the squat.

This is particularly why exercises where the hip is not actively going through flexion (i.e. leg extensions or reverse Nordic curls) are better for engaging the RF than the squat. Then, the muscle is anchored to a non-moving structure and not opposing hip extension, allowing it to contract. Fun fact: if you want to increase RF activation during the leg extension, adjust the pad so it is all the way back, which will allow you to lean backward and increase the angle at the hip even more. This is also why I think the Freemotion quad machine is an underrated exercise for overall quad development (and unfortunately is not very popular in gyms anymore).

When Hypertrophy Research Confirms Kinesiology Concepts

To hell with what we know about biomechanics, why do I squat all the time and feel as if my RF is observably larger? If you only squat, there are some likelihoods that may co-exist. One of them is, as your training progressed, the fat around your legs may have decreased. Fat loss can create the optical illusion that something has gotten bigger because it is more defined. Further, we know that squats are great for the three vastus muscles. The vastus intermedius is located right behind the RF. If this muscle is getting larger from training, it will push against the RF from behind, potentially creating a false sense that the RF is growing from squats, especially since overall quad girth has increased in diameter. Without opening up a can of worms here, another plausible explanation is that you use PEDs, like testosterone. Testosterone injections can increase muscle mass without any training stimulus at small-to-moderate doses (1).

But this part of the article does not care about speculations from our firsthand perception. It cares about the published evidence that fortifies what we know about human movement.

There are numerous studies that have shown squats do not result in much, if any, growth of the RF (2, 6, 8-10, 12). A more recent study found the RF cross-sectional area (CSA) was not correlated with squat 1 rep max, indicating that the RF does not contribute to force production during this exercise (7).

Aside from what we know about biomechanics, there is some research that suggests the nervous system preferentially recruits monoarticular muscles (i.e. the three vastus muscles) over biarticular muscles (i.e. the RF)(3, 4). This makes sense, since contraction of the RF during the squat would actually be counterproductive to the exercise.

Do you want big quads? Squats can surely help with that. But your quads would be much bigger if squats weren’t the only exercise that you did for your quads.

About the Author

Alex Tran is a personal trainer, nutrition coach, and virtual coach that is based in Chicago, IL. He has a Master’s degree in Applied Exercise Science with a Sports Nutrition emphasis. Additionally, he is a Certified Strength & Conditioning Specialist through the National Strength & Conditioning Association. To see more of his content, follow him here: instagram.com/atperformance_. To contact him, follow this link.

References

(1) Bhasin et al. (1996). The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men.

(2) Earp et al. (2015). Inhomogeneous Quadriceps Femoris Hypertrophy in Response to Strength and Power Training.

(3) Ema et al. (2016). Unique activation of the quadriceps femoris during single- and multi-joint exercises.

(4) Ema et al. (2017). Effect of prolonged vibration to synergistic and antagonistic muscles on the rectus femoris activation during multi-joint exercises.

(5) Floyd, R. (2012). Manual of Structural Kinesiology.

(6) Fonseca et al. (2014). Changes in exercises are more effective than in loading schemes to improve muscle strength.

(7) Kojic et al. (2021). Quadriceps femoris cross-sectional area and specific leg strength: relationship between different muscles and squat variations.

(8) Kubo et al. (2019). Effects of squat training with different depths on lower limb muscle volumes.

(9) Pareja-Blanco et al. (2017). Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations.

(10) Ploutz-Snyder et al. (1995). Resistance exercise-induced fluid shifts: change in active muscle size and plasma volume.

(11) Ribeiro et al. (2022). A Brief Review on the Effects of the Squat Exercise on Lower-Limb Muscle Hypertrophy.

(12) Zabaleta-Korta et al. (2021). The role of exercise selection in regional Muscle Hypertrophy: A randomized controlled trial.