Anatomy Of A Squat

Anatomy Of A Squat

Anatomy Of A Squat

Here we’ll explore the:

Different Phases Of A Squat Motion

Simply put, there is a starting, descent, pause, and ascent phase in a squat exercise. Technically speaking, after the starting position, the phases of the squat are:

  • Eccentric phase. This is where the body descends into the squatting position. During this phase, muscles will be eccentrically contracting. This means they lengthen to control the movement speed and squat depth.
  • Isometric phase. Some people will avoid this part of the squat altogether. However, it’s important to note. The isometric phase or isometric contraction is when there is no visible movement. Further, it occurs after the eccentric phase and just before the concentric phase.
  • Concentric phase. This part of the squat is what most people consider the actual exercise. In a concentric contraction, muscles of the hip and knee are shortening to pull on the bones and joints. Consequently, the body returns to a starting position.

The different phases of a squat are important to know so you understand which muscles are responsible for what during the movement. 

Joint Motions During A Squat

Most people just think of their quadriceps doing all the work during a squat. However, a proper squat requires range of motion at the foot and ankle complex, knee, and hip complex. 

Foot And Ankle Complex

During the eccentric motion of the squat, you will need good ankle mobility so the lower leg can migrate forward as the body descends. Without this forward motion of the lower leg (shin), you won’t be able to keep balance over your center of gravity. In this case, one of three things will happen:

  • You won’t be able to achieve ideal squat depth
  • You’ll fall backward or tip excessively forward to balance the weight
  • Your heels will lift off the ground

Technically speaking, you’ll need good dorsiflexion at the ankle. This allows the tibia and fibula to track forward.


There will be knee flexion and extension when squatting. During the squat descent, you’ll move into knee flexion. And during the ascent portion, it will move into knee extension. There shouldn’t be unwanted movement at the knee such as knee valgus (one knee or both moving inward) or knee moving outward (abduction at the hip)

Hip Complex

Also known as the lumbopelvic hip complex, the joint motion here is critical to perform a good squat. During the descent (eccentric phase) the hip will move into flexion, where the muscles in the front shorten and the muscles on the backside lengthen. Then, during the ascent (concentric phase) the joint motion is hip extensions. When trying to target the gluteus maximus, you’ll need good range of motion at the hip to get full lengthening and then shortening of this large muscle. 

Muscle Anatomy During A Squat

Knowing the muscles during a squat will help you correct bad technique and get the most out of the exercise. As a reminder, a muscle will serve one of three different functions during an exercise. It will either:

  • Be the most important muscle to produce the movement at a joint. This is called the “prime mover”. In technical terms, it is also called the agonist. Agonists will concentrically contract during the ascent of a motion. And, a prime mover is what most people think of when they are trying to target a muscle.
  • Lengthen to allow movement to occur. This is the opposing muscle and the term is the antagonist. It shortens (concentrically contracts) during the descent and lengthens (eccentrically contracts) during the ascent. It’s easy to forget about the role this type of muscle plays, but it’s important because if it needs to lengthen fully for the motion to occur.
  • Help the prime mover but not be responsible for the majority of the work. The name of this muscle function is “synergist” or assistant mover.
  • Prevent unwanted motion. This muscle function is a stabilizer and prevents the body from moving beyond the intended exercise.

Muscular Anatomy At The Foot And Ankle Complex

When descending into the squat, the calf complex (soleus and gastrocnemius) will eccentrically contract to allow the tibia to track forward. At the same time, the anterior tibialis, or the muscle right in front of the shin, will concentrically contract and pull the lower leg forward. 

Likewise, during the squat ascent, the gastrocnemius and soleus will concentrically contract to return the lower leg to a starting position. In a wide squat stance or if you’re standing with the feet externally rotated, this type of ankle mobility won’t be needed. This is because, in these instances, the body can maintain its center of gravity with a wider base of support.

Muscular Anatomy At The Knee Joint

Remember, during a squat, there will be knee flexion and extension. Therefore, as the body lowers into the squat, the hamstrings (attaching the femur and lower leg) will shorten and the quadriceps complex will lengthen during knee flexion. 

During the descent of the squat, hamstring muscles will eccentrically contract and lengthen. These muscles include:

  • Biceps femoris
  • Semimembranosus
  • Semitendinosus

These muscles cross the knee and the hip. Therefore they also assist the prime mover at the hip as synergists. 

During the ascent of the squat, the quadriceps will shorten, concentrically contracting, to return to a standing position. The muscles of the quads include:

  • Vastus lateralis
  • Vastus intermedius
  • Vastus mediails
  • Rectus femoris

The rectus femoris is the only muscle in the quadriceps group that crosses both the knee and hip joint. This is important because, as a hip flexor muscle too, it can become tight and shortened over time. This will impact the ability of the upper leg portion of the lower body to perform even a bodyweight squat correctly.

Muscular Anatomy At The Hip Complex

The hip extensors will serve as the prime movers during the ascension of the squat exercise. Whereas the hip flexors will oppose the movement and lengthen during the ascension.

Hip muscles that are a hip extensor include:

  • Gluteus maximus
  • Gluteus medius
  • Piriformis

The glute max will be the prime mover, or agonist, during the motion. It is a large muscle and lies most superficial relative to the other muscles of the hip. The gluteus medius is somewhat smaller. It’s more responsible for hip abduction and hip external rotation. However, the posterior fibers also produce hip extension. Therefore this muscle is also a synergist.

The piriformis is a small and deep assisting muscle of the hip complex. Given it is a synergist, it should not be doing as much work as it sometimes does. However, sometimes the glute max is unable to produce the movement fully. When this happens, the synergists step in and help out. Over time this can be problematic because the muscles will become excessively shortened.

Ways To Perform A Squat Exercise

There are different ways to perform a squat, depending on what you’re trying to do. However, when looking for ideal squatting mechanics it should be basic. To test squatting mechanics, you should perform a bodyweight squat, starting with the feet only hip to shoulder-width apart. The feet should point straight ahead and the person should squat roughly to the height of a chair. If they can squat deeper without compensation this is good. Performing this movement, or with the arms up as an overhead squat, will give a fitness professional an idea of how well the body can perform the exercise.

However, most people who exercise will look for a squat variation. Variations are practically limitless since most lower body movement requires squatting. Therefore these are some squat variations:

  • Split squat, also known as a stationary lunge
  • Wide stance squat, sometimes called a sumo squat
  • Single-leg squat 
  • Leg press

The list goes on and will vary with speed, resistance, and lower body positioning.

Errors In Squat Form

Whether known or unknown, most people have errors in squat form and need correction. The most common reason for these errors is due to hip mobility. Most people spend the majority of their day sitting. This means the hip flexors will be shortened for most of the day. Over time, they’ll stay in a shortened state. When this happens, the opposing muscle group will be in a lengthened state. So when the hip flexors are consistently shortened, the glutes will be consistently lengthened. This will impact squat form, making it more challenging for the glutes to do their primary job. Instead, they’ll recruit other muscles such as the piriformis and hamstring groups to do more work. This ultimately alters the way someone squats and can decrease their ability to lift more weight or increase their chance of injury.

Common errors in squat form include:

  • Feet excessively turned out
  • Lack of ankle dorsiflexion
  • Lower back arching (weakness in core stability)
  • Lower back rounding (weakness in spinal extensors)
  • Heels lifting off the ground

Jump Squat

Use a jump squat as part of a power, HIIT, or functional fitness workout

Anatomy Of A Squat: EMAC Certifications

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