Here's what you need to know...

There are people who squat shallow because they're ignorant or delusional. But there are others who do so for good reasons, and they get good results. The parallel squat is an arbitrary standard developed by powerlifters for powerlifters. It's not necessarily best for you. For many, deep squats are useless for quad activation. ATG squats allow the quads to take a vacation and they never develop. Olympic weightlifters - known for being the deepest squatters - often use very shallow, overloaded squats in their training. ATG squats are only specific to one sport - Olympic weightlifting. Many sports would benefit more from partial ROM. Whether or not you can squat deep without "buttwink" is mostly a factor of bony hip structure. There's no rule saying you have to choose between ATG and partial squats. You can do both.

A Quarter Squatter! Get Him!

You've seen this guy at the gym. Just by looking at him you know exactly what's going to happen when he steps into the squat rack.

Sure enough, it happens: he gets under the bar, drops one-fourth of the way down, and stands back up.

Yep, he's a dirty partial squatter. Probably brags to his friends about his new 1RM even though his knobby knees barely bend when he squats. Everyone knows that the only real squat is "ass to grass, bro!" Right?

Well, not so fast.

It depends on the rationale. It's one thing if you squat shallow because you're a self-delusional punk just trying to impress your bro's by putting more plates on the bar.

It's quite another thing if you do partial squats for one of the legitimate reasons. And yes, there are legitimate reasons.

Is it really necessary to "leave a stain on the floor" to get the most from your squats? Or do various types of partial ROM squats have their place in a legitimate training program?

4 Questions to Ask

There are at least four different criteria for assessing proper squat depth for you and your objectives:

What's the best depth for optimum strength gains? What's the best depth for optimum muscular gains? What's the best depth for optimum sport specificity? What's the best depth for maximal safety?

Let's break it down.

Squat Depth and Strength Development

When it comes to using squats to get stronger, the first thing to recognize is that squatting to various depths will change the magnitude of stress experienced by the different muscles in your legs.

For example, in most people, squatting ATG puts especially high tensions on the vastus medialis (part of the quadriceps complex). So if you're a bodybuilder looking to develop that "teardrop" appearance just above the knee, ATG squats are a useful tool.

And looking at this question more generally, all else being equal (which is rarely the case), the deeper you squat, the greater the stress to all the muscles involved: glutes, quads, hams, adductors, and so on.

Now here's a counter-intuitive but common exception to that general rule. During a recent conversation with T Nation contributor Christian Thibaudeau, I mentioned how I feel my quads much more during partial squats as opposed to deeper squats.

He told me that from his experience, tighter people, as a rule, are able to exploit the stretch-shortening cycle much more effectively than people who aren't so tight.

Think of it this way: If you've got fairly tight hamstrings and glutes, when you squat deeply enough to stretch those muscles taut, you'll be able to use the elastic rebound to propel yourself out of the hole without needing much contribution from the quads.

If, one the other hand, you squatted to a higher bottom position, your glutes and hams wouldn't be placed in a significant stretch and the quads would be pretty much the only muscle remaining to tackle the job.

In other words, there are in fact cases where partial squats are more effective than ATG for specific strength-development purposes.

Squat Depth and Muscular Hypertrophy

If relatively shallow squats are sometimes superior in terms of strengthening specific leg muscles, then those same squats would also have potential for better size development of those same muscles.

Now, of course, the idea of using full range of motion is pretty much the first commandment in the bodybuilder's playbook. Got it. But muscular growth isn't only a function of ROM. In truth, it's a function of doing gradually more and more work.

Technically, work is defined as displacing a mass for a specific distance. This being the case, you could actually end up performing the same amount of work (or even more total work) by moving a heavier weight for a shorter distance than you could moving a lighter weight for a longer distance.

In other words, it's possible to overcome the disadvantages of shorter squat ROM by using heavier weights.

Note: An athlete with short femurs who squats to parallel with 500 pounds is doing less work than a lifter with long femurs squatting 500 to parallel. He's moving the weight over a shorter distance. No two lifters are the same, so why should they all use the same squat position?

So, less ROM can be compensated for by using more load. In most cases, the guys with the best quads are those with the shortest femurs.

Similarly, the lifters with the best pecs are often the most "barrel-chested." The guys who have the most developed musculature usually have short levers, which means - you guessed it - they always use shorter ROMs on everything they do, simply because of their unique anthropometry!

Now, this isn't to say that partial squats are superior to ATG, but rather, they aren't necessarily inferior. It simply depends on the individual and the context.

Squat Depth and Sport Specificity

It's interesting to note that the two depth standards that most people use for assessing the correctness of a squat - parallel and ATG - come from powerlifting and weightlifting, respectively.

Powerlifters need an easy, objective way to ascertain whether or not a lifter squats to the same depth as his or her fellow competitors for the sake of fairness. No surprise, squatting to a thighs-parallel position makes a lot of sense for that purpose.

Olympic weightlifters, on the other hand, benefit from catching snatches and cleans in the deepest possible squat position. The deeper you can catch the bar, the less high you need to pull it.

But what if you're not a powerlifter or a weightlifter? What if you're a 6'4" tennis player with long femurs? Or what if you're a sprinter or a baseball catcher?

When assessing ideal squat depths for athletes, there are a few things to think about:

What hip, knee, and ankle angles are typical for the sport skills in question? Is the athlete commonly required to create high levels of force from deep squat positions? Is a high level of lower body strength required for the sport? Is the athlete often subjected to lower-body injury risks that could be at least partially mitigated through the use of a specific squat depth as part of a strength and conditioning program? Does the athlete have orthopedic issues that would predicate the use of a specific squat depth for safety reasons?

As you can see, a "one size fits all" approach to squat depth for strength development is myopic and sometimes dangerous.

Sure, ATG squats are an effective tool when used appropriately in the right contexts, but they're not the only tool in your toolbox. Don't fall prey to dogmatic conventions such as the idea that squats "must" be performed ATG.

Squat Depth and Safety

Assuming good orthopedic health, the primary limitation to safe squat depth is the ability to maintain a neutral lumbar spine throughout the entire movement.

Flexing or rounding the low back under load is pretty much universally considered to significantly increase the risk of lumbar spine injury.

It's often assumed that cases of "buttwink" in some squatters is due to short hamstrings, but something called Codman's paradox places that assumption in question.

While it's true that the hamstrings undergo shortening at the hip during deep squats, they also undergo lengthening at the knee at the same time.

In essence, hamstring lengthening at the hip tends to be cancelled out by hamstring lengthening at the knee, so net hamstring length tends to remain unchanged during squats for most people.

A much more likely cause of lumbar flexion is bony hip structure.

Put simply, at a certain point in the squat (different for all people), the femur jams up against the hip socket, making further movement at the hip an impossibility. The only way to achieve a deeper squat from that point is to flex from the lumbar spine.

Now if you're a highly competitive athlete, such as an Olympic-style weightlifter, that might be a risk you'd be willing to take. It's really a highly-individualized risk-reward equation.

If you're going to risk a debilitating lumbar injury because you're deep-squatting with a flexed lumbar spine, are you sure you're enjoying a commensurate reward to offset that risk?

It's worth mentioning that Mark Rippetoe has made the point that deep squats can in fact be safer than partial ROM squats, since when you squat ATG the resulting hamstring tension (only experienced at the bottom of a deep squat) tends to offset the high patella-femoral ligament tensions.

While this is an important and normally overlooked point, it's doesn't automatically follow that partial ROM squats are categorically dangerous. It's really about matching the best tool for the best job.

Morality Disguised as Biomechanics?

Interestingly, people rarely question the use of various ROMs for other exercises such as presses or pulls. For some reason, this debate only seems to raise its ugly head when it comes to squatting.

And usually the critique of partial ROM squats doesn't come from a rational standpoint. Instead, at its core, it's a form of morality disguised as biomechanics.

Much like the raw vegan who justifies her moral indignation about meat by listing the health reasons for her choices, often hardcore lifters who criticize partial ROM squatters on biomechanical grounds are really just trying to reinforce their own sense of superiority.

Few of us criticize the use of varying grip widths on bench presses or starting bar positions on deadlifts. We simply view these choices as tools to be intelligently applied in the training process.

Why then should squat ROM be viewed any differently? Answer: It shouldn't.

There's no rule saying that you have to choose between ATG and partial squats. You can, and probably should, do both types in your training.

Related: Squat Right for Your Type

Related: Mark Rippetoe on the squat