The Real Science of Squat Depth

Ass-to-Grass vs. Parallel Squats

From One Extreme to the Other

In the past, I would have said the most common technique error in the gym was squatting too shallow and failing to reach proper depth. Fast-forward a decade and I'd still agree that improper squat depth is the most common issue. However, the problem is now on the opposite end of the spectrum – too deep. The industry standards for what's considered proper depth have gone from one extreme to the other.

This makes perfect sense. Before the surge in online instruction and YouTube videos, half squats and partial reps were quickly becoming commonplace. Rather than providing the appropriate level of instruction, the quick fix for the industry was suggesting rock bottom or "ass-to-grass" squats.

Soon, anyone performing shallow squats would be called-out by your typical half-educated lifter and told that their squats were nothing short of iron game heresy. Even worse, posting a YouTube video with anything but ass to-grass squat technique would be met with a flurry of hate comments... even if the video was taken at a powerlifting meet and the lifter hit the legal depth.

As a result, many lifters began going to any lengths necessary to increase their range of motion, flexibility, and mobility, with the end goal of reaching as deep of a squat as possible, even if it meant sacrificing proper mechanics. Although you're still likely to run into your average newbie performing half squats and quarter squats, the majority of dedicated lifters now squat with excessive depth by allowing their bodies to collapse at the bottom of the movement.

A key factor that's led to the promotion of excessive squat depth is mobility assessments that demonstrate variations in human anthropometry. These individual differences have led to the assumption that each person has his or her unique set of protocols when it comes to ideal squat depth. Unfortunately this notion is completely flawed and inaccurate.

After spending well over a decade coaching hundreds of athletes of all different shapes, heights, ages, and sizes, the one thing I can tell you is that while maximal range of motion and mobility boundaries vary greatly from person to person, proper squat depth, mechanics, and ideal range of motion are very similar from individual to individual.

In fact, with proper training and coaching, a 5-foot female gymnast and a 7-foot male basketball player will have remarkably similar squats. In essence, individual differences in anthropometrics only indicate maximal range of motion, not ideal or proper range of motion.

On a similar note, just because an individual can squat to extreme depth with no apparent aberration in technique or spinal alignment (i.e., a butt wink) does not suggest this is their ideal squatting depth. This only indicates what their maximum depth is. In fact, these same individuals typically demonstrate significant laxity in their hips and hypermobility throughout their body, both of which can be highly problematic.

It's important to confess I had many athletes squatting with ATG depth for well over five years. These were done under strict control using "textbook" technique. However, after seeing the joint issues, constant tightness, continual soreness, heightened inflammation, and altered movement mechanics (including deterioration of the gait), I began to realize that ATG wasn't optimal.

In fact, I soon understood why foam rolling and soft tissue work were quickly becoming so popular. If the lifter was going to incorporate excessive range of motion, then soft tissue work was essential. However, proper mechanics warrant no such treatment as the movements themselves provide the very benefits that others seek to gain from soft tissue modalities.

It was these very issues that made me realize that while squatting to such extreme depths was visually appealing to the eyes and ego (for ATG fanatics), the benefits didn't outweigh the physical ramifications.


Many in the industry suggest the squatting technique of babies is the gold standard for squat mechanics. In reality this assumption couldn't be more flawed. First, babies represent the counter opposite of proper motor control and ideal muscle function – their movement and physiques are crude and underdeveloped.

These miniature humans barely have the stability, motor control, or strength to balance on two legs, yet we're looking to them as the epitome of optimal muscle function and mobility. If a baby's movement represents the epitome of optimal muscle function, then perhaps having the ability to suck on your toes should be the new standard for measuring hip mobility.

Babies actually have more bones in their bodies than adults, as many of their bones simply haven't fused. This also leads to an exaggerated flexibility and excessive range of motion that adults shouldn't be attempting to replicate.

Many who assert the ideology of using a baby's squat to represent the ideal squat pattern are quick to point to the "third world squat" often performed in other countries, particularly throughout Asia. In a third world squat, the individual simply relaxes into the deepest squat position where the butt is nearly touching the floor. Because this is almost identical to what babies do, it's assumed that society and technology are responsible for ruining people's squat mechanics. Now here's where things get interesting.

The third-world squat should in fact be a position that most humans are capable of performing. And yes, various faults in our society have contributed to the elimination of this ability in many adults.

Here's the catch: The third-world squat and a strength-training squat are two entirely different movements requiring completely different recruitment patterns. In fact, the third-world squat is a passive squat where little if any muscle activation is evident as the individual simply hangs out on their joints, tendons, ligaments, and connective tissue.

In contrast, a strength-training squat is an active squat. In this case, the lifter should be firing his muscles aggressively in order to maintain stability, motor control, force, and muscle stiffness, all of which are essential for taking strain off the joints and using the muscles as shock absorbers. When a passive squat is incorporated into strength training scenarios with heavy loads, the muscles are in an overly relaxed state, particularly during the eccentric motion, thereby stressing the joints and connective tissue rather than the muscles.

Instead of using the reciprocal muscle groups to pull the lifter into the proper position via high levels of co-contraction, the individual relaxes/collapses to varying degrees and relies on both gravity and the external load to pull him into the rock-bottom position.

In such a scenario the lifter is exhibiting low levels of proprioception and muscle activation as muscle spindle recruitment is predicated on increased muscle stiffness and co-contraction, both of which are absent during the passive squat. As a result, the squat pattern resembles a very sloppy and uncontrolled movement rather than a tight and crisp motion.

Performing mobility work to become more mobile seems logical. However, this can be the very factor that limits mobility. Overdoing it on mobility exercises, stretching, and soft tissue work can desensitize muscle spindles, allowing the lifter to perform movements such as squats with excessive ROM. This leads to localized chronic inflammation, which over time is the very thing that limits mobility and range of motion.

The single biggest problem with a majority of squat patterns isn't mobility, but lack of stability, tightness, and motor control. As the lifter gains stability, his body naturally begins to perform the movement pattern with the ideal range of motion. In other words, gain stability first and optimal mobility naturally follows, not the other way around. The last thing you want to do is gain ROM that you can't stabilize.

Many lifters will claim that ATG squats are superior to parallel squats simply because they're more difficult, intense, and strenuous on the body. In reality the opposite is true. Parallel squats require markedly greater activation, muscular tension, concentration, mental fortitude, intensity, and overall strength.

Supporters of ATG squats suggest that the increased load the lifter is capable of handling on parallel squats is simply a form of cheating as they're making the exercise easier. This notion is false.

Yes, it's true that the lifter won't be capable of handling as much weight during ATG squats. However, this is a byproduct of decreased motor unit recruitment and reduced muscle activation necessary for achieving such a collapsed position. As a result, the lifter is punished with compromised contraction strength and reduced force-producing capabilities.

The appearance of the lighter load feeling heavier is simply a byproduct of faulty mechanics, giving the lifter the illusion that he or she is doing more work. In reality they're doing less work as they're reinforcing neuromuscular inefficiency and making the movement feel unnecessarily taxing and physiologically exhausting.

On the other hand, a proper parallel squat rewards the lifter with greater force-producing capabilities as every muscle fiber is firing maximally. This requires the highest levels of concentration, as well as mental and physical intensity as there can be no weak links or energy leaks. Essentially, this maximizes load, power, speed, motor unit recruitment, intramuscular tension, and hypertrophy, all of which are compromised during ATG squats.

In essence, with parallel squats the lifter is controlling the load. With ATG squats the load is controlling the lifter.

Besides being incredibly strong and explosive, Olympic weightlifters have some of the strongest tendons, ligaments, and connective tissues of any sub-population. This allows them to drop excessively deep under heavy loads with few immediate injuries, relatively speaking.

Olympic Lifter

In reality, many Olympic weightlifters have flawed squat mechanics that often display a significant valgus knee collapse with an excessive eternally rotated foot/ankle complex, both of which are common by-products of reaching excessive squat depth. Rather than seeing the squat as a therapeutic movement, these athletes often have minimal concern for squat mechanics. They recognize that the sole purpose of the squat for their sport is to reach the most extreme depth they can handle with the ultimate goal of cleaning or snatching the heaviest possible weight.

In fact, many of these extreme depths would be impossible without the assistance of weightlifting shoes as their bodies are able to use this unnatural elevation and lateral support to assist in further degradation of natural body mechanics.

It should be noted that not all Olympic weightlifters demonstrate flawed squatting mechanics. Some of the all-time greats, including Pyrros Dimas, were known for avoiding excessive depth, particularly during training, as extreme positions were often saved for the most dire circumstances such as max attempts in competition.

It's important to understand that powerlifting rules and guidelines aren't based on optimal human mechanics; they're based on specific criteria for allowing visually subjective judging to be streamlined for competitive circumstances. Although many powerlifting organizations require depth that represents excessive range of motion (usually by a few inches), some organizations hold criteria that are actually quite close to ideal squat depth in respect to optimal human mechanics.


Ironically, some of the strongest powerlifters in the world utilize squat mechanics that just so happen to represent ideal squat depth. They accomplish this by employing extremely controlled eccentric (lowering) movements, stopping approximately at parallel, maintaining maximal tightness, and avoiding any type of collapse at the bottom position. In fact, the type of records they break would be impossible to perform safely with ATG squats.

Admittedly, a majority of research studies suggest deep squats are more effective and healthier on the joints than partial squats or parallel squats. These results are to be expected when comparing deep squats to partial squats. However, the fact that deep squats have been shown to be safer and more effective than parallel squats can be attributed to one factor – faulty research and flawed application of practical training methods.

Unfortunately, most research studies involving heavy strength training are carried out by lab rats that have no clue how to properly squat or coach these basic movements. I've actually had the opportunity to witness many kinesiology investigations at university settings and to suggest there's a lack of proper coaching and cuing is an understatement.

The fact that ATG squats appear superior to parallel squats during these investigations can be traced back to improper execution of the squat, namely lack of posterior chain activation due to faulty hip hinge mechanics. Because most individuals don't hinge adequately during the squat (unless properly instructed), the glutes and hamstrings are nearly dormant until excessive depth is reached.

Excessive squat depth is necessary in these circumstances to activate the knee stabilizers and posterior chain, both of which would've been fully activated throughout the entire motion if in fact proper parallel squat mechanics were used.

Activating the posterior chain during squats is critical for protecting the knees and surrounding joints. This can be done either by properly hinging throughout the entire motion (which requires adequate coaching) or by employing excessive depth, which promotes inflammation, spasticity, dysfunction, and faulty mechanics.

When determining proper arthrokinematics and positioning for any movement, it's critical to examine the scientific principles foundational to neurophysiology, skeletal muscle physiology, motor learning, and biomechanics.

If the mechanics for a movement such as a squat are correct, then these concepts will not only be practically displayed within the muscular action itself, but these principles will be congruent with each other. Let's examine some of these principles to illustrate how they align and affirm the parallel position as the optimal squat depth.

1. The Stretch Reflex Redefined

Many lifters are quick to justify their excessive squat depth by suggesting they're taking advantage of the stretch reflex. However, this argument is inherently flawed. In fact, what many consider to be effective utilization of the stretch reflex is actually not the stretch reflex at all.

Rather it's a rebound effect that's a byproduct of using their tendons, ligaments and connective tissue as flimsy and fragile springboards to bounce off of. This has little to do with the stretch reflex and is in fact opposite to how you would ideally want to activate the stretch reflex mechanism.

To optimally employ the stretch reflex, a heightened level of structural tightness and musculoskeletal stiffness must be present as this is fundamental to how muscle spindles operate. Muscle spindles are the key players when it comes to activation of the stretch reflex mechanism. When muscles demonstrate minimal stiffness qualities such as that commonly seen with excessively deep squats, this disengages or inhibits muscle spindle activation, therefore minimizing the involvement of the stretch reflex mechanism.

In essence, the individual has regrettably achieved the ability to override his body's natural protective barriers and force-production mechanisms that would normally resist an exaggerated stretch. As a result, the body's ability to create optimal joint angles, fine-tune position, and make subtle adjustments to technique and mechanics becomes greatly compromised as the proprioceptive mechanisms aren't functioning as they should.

2. The Transfer Effect

It would be one thing if these effects were only isolated to the strength training session itself. However, based on principles of motor learning we know that movement transfers and impacts other related motions.

Therefore, performing movements, or in this case squats, with excessive ROM not only negatively impacts the body during the actual training session, but the effects are long lasting with detrimental carryover to other activities including running, jumping, kicking, lunging, hinging, and even walking. This unwanted-transfer effect is applicable to the following points as well.

3. Length-Tension Relationship

Researchers have concluded that a muscle will produce the most tension and force when sarcomeres are in the moderately stretched position. This would indicate that some stretch is good, but too much can lead to sub-maximal results in terms of muscular tension and cross-bridging. For the squat, that's somewhere around parallel.

4. Anatomical Levers

Utilizing angles and positions that maximize leverage and torque production is a key concept in biomechanics. This involves 90-degree angles, perpendicular positions, and parallel joint segments.

The ATG squat couldn't represent a more biomechanically dysfunctional position when it comes to maximizing anatomical lever arms. In contrast, the parallel squat takes full advantage of these constructs by optimizing moment arms (the length between a joint axis and the line of force acting on that joint) and leverage.

5. Elastic Energy

Collapsing and bouncing out of the bottom of a squat not only wreaks havoc on joints, but it reinforces the action of minimizing torque, power production, and movement efficiency. At best, this dangerous maneuver will bounce the lifter back to a position he would've squatted to in the first place (depth-wise). However, because of the reduced muscular activation, there will be an obvious sticking point with significantly diminished torque throughout the concentric (lifting) movement.

In contrast, the parallel squat represents the epitome for maximizing muscular stiffness, proprioceptive feedback, and elastic energy, as the muscles are stretched to their maximum range while maintaining optimal stiffness qualities.

6. Squat Like a Human

The parallel squat represents a movement pattern where key principles foundational to neurophysiology, skeletal muscle physiology, motor learning, and biomechanics are congruent with each other. So it's no coincidence that parallel squats are the ideal squat method for humans as the concepts involved are not based on man-made rules but, instead, predicated on scientific principles that remain constant from human to human. Unless you're from another planet, there's no reason to think your body functions differently.

Although some lifters can temporarily "get away" with excessive squat depth, eventually it will produce negative ramifications. I've seen this numerous times in lifters I've consulted with. They explain how they've been squatting to extreme depth for years with no pain or discomfort, but eventually it hits them like a ton of bricks.

There seems to be a tipping point where a once seemingly healthy lifter begins to have incredible pain in the hips, knees, and low back, as well as other physical symptoms. For some this may occur after months while for others it may take years. Regardless of the time frame, overall strength and performance (not to mention muscle function and joint health) would have improved to a much greater degree had proper mechanics and depth been employed in the first place.