By Letty Krueger, PT, DPT, CSCS
One of the most basic functional assessments is to watch someone squat. There are many of reasons one may not be able to maintain a parallel tibia:torso ratio, break parallel with the crease of the hip, or lose sagittal plane alignment. However, the cause of dysfunction may not be what it seems.
The gold standard (and only true standard) of the squat movement is that the crease of the hips pass below the vertical height of the knee. This position is relatively difficult for some to achieve, while others seem to sit their hamstrings down on their calves rather naturally.
In the former group, where one has trouble squatting to parallel, it’s easy to diagnose “tight hips.” But, rolling, mashing, smashing, stretching, and mobilizing the hips will only get you so far. We must also consider anthropometric differences between individuals. There are obvious anatomical variances between individuals including shape, alignment, and relative angles of attachment of specific joints. Due to these skeletal variations, the ability to move through the functional movement of a squat will be entirely different from one to another. Bone to bone contact of a joint is the ultimate limiting factor in the amount of mobility a joint has, which is directly dictated by the shape and position of that joint.
Let’s focus specifically on the hip joint. The hip joint is a ball-and-socket type joint where the femoral head fits into the cup-shaped acetabulum. Squat variations begin most simply with the length of the femur. The femur averages 26% of the body’s total height (Bogin, 2010). Two individuals, of the same height, with a different torso:femur ratio, will have a markedly different squat. Someone who is taller, with a femur length that comprises >26% total height will not only have to descend through a greater range of motion, but will also have more difficulty maintaining balance over their base of support. In order to keep weight over the midfoot, these individuals may have a greater forward leaning squat posture, adopt a wider stance, or increase hip abduction/external rotation angle.
More specifically, we’ll take a look at the proximal femur. The neck of the femur extends infrolaterally from the head of the femur to meet the shaft of the femur. This angle averages about 125 degrees, but can vary with age, stature, gender, and pelvic width. When this angle is >139 degrees, it is known as coxa valga. Conversely, coxa vara, refers to femoral neck angle <120 degrees (Peele, 2005). The coxa valga neck angle will increase the chance of bone-on-bone contact between the pelvis and the femur at the bottom of a squat. The coxa vara neck angle would likely be more comfortable at the bottom of the squat due to less bony contact.
To make matters more complicated, a similar femoral neck angle can cause squat variations due to differing femoral neck length. Increased length of the neck, means the head extends further off of the femur, and is able to protrude deeper into the acetabulum.
Lastly, the neck of the femur can be in an anteverted, or retroverted position. Anteverted refers to the forward angle of the neck, where the femoral head is positioned anterior to the shaft. Retroverted refers to the opposite, where the neck is angled backwards, and the femoral head it positioned posterior to the shaft. Variances between these angles have been shown to be at much as 24 degrees (Zalawadia, 2010). Anteversion at the femoral neck will result in internal hip rotation that appears to be excessive, and an external rotation range that appears to be limited. This is because, in order for a femoral head, that is positioned excessively anteriorly to the femur, to fit into the acetabulum, the rest of the femur must be rotated inwards. These individuals will prefer a narrower stance, and lower extremity kinematics will predispose them towards a pronation pattern (sub-talar pronation, tibial/femoral internal rotation, and anterior pelvic tilt). They might need a little more work increasing external rotator strength and core control rather than performing sumo deadlifts, that force the femur into an abducted and externally rotated position (which will likely be uncomfortable, and potentially create issues down the line).
Conversely, someone who has femoral retroversion will likely have bone-to-bone contact sooner in the hip flexion range of motion compared to those with a more anteverted angle of alignment. With the difference in alignment as much as 24 degrees, that is the difference between squatting “ass to grass,” and not being able to go below parallel. These individuals, with femoral retroversion, will feel a boney block when they attempt to squat narrow and therefore adopt a wider squat stance, while the more anteverted femoral neck will squat narrow without a problem, but experience pain with wide squatting.
To make matters even more interesting, variations in the angle, shape, and depth of the acetabulum can have a profound effect on how the femur will move within that socket.
Likewise to the femur, the acetabulum can be angled anteriorly (anteverted), neutral, or be angled posteriorly (retroverted). Anteverted hip sockets will be less likely to have bone-to-bone contact at the bottom of a squat, whereas a retroverted hip may be more restricted at the bottom of the movement. This difference has been shown to be upwards of 30 degrees (D’Lima, 2010). This means that the most anteverted acetabulum will have up to 30 extra degrees of flexion, but may find it harder to lock the hips out in extension. On the other hand, the most retroverted acetabulum will have up to 30 extra degrees of hip extension making it easier to extend at the top of a squat, but more difficult to hit depth.
Hip socket depth, or “center-edge angle,” is also a critical variance that can range immensely. A deep socket will cause a feeling of restriction earlier in the depth of the squat due to bone-to-bone contact between the acetabulum and the femoral head. This will likely cause pain, or compensation from the lumbar spine. A shallow socket will likely be comfortable at the bottom of a deep squat because there is no bone-to-bone contact preventing end range depth, but is innately more unstable due to the increased range, and will have a weaker lock out at the top.
If you happen to be born with relatively short femurs, have a shallow anteverted acetabulum and a coxa vara femoral neck, you’ll likely have no problem sitting your glutes onto your heels and duck walking a 5K. On the other hand, if you have relatively long femurs, with a deep retroverted acetabulum and a coxa valga femoral head it will be more challenge to drop deep into a squat, and you’ll likely adopt a wider stance with a shallow bottom position. These individuals may also posteriorly tilt the pelvis and flex the lumbar spine in order to squat more deeply once the available range of motion at the hip joint is exhausted, and therefore train outside their anatomical limits.
To complicate matters even more, it’s also been shown that the same individuals’ left and right hip can be significantly different. The angle or anteversion/retroversion of the femoral head can be up to 20 degrees different from side to side (Zalawadia, 2010). In these instances, training in a symmetric set up could be inherently wrong.
Essentially, people won’t squat the same, and people shouldn’t squat the same. The ability to achieve a specific range of motion in a squat is determined moreover by anatomy than by strength and mobility. Imagine making two tight fists and pressing them together as hard as possible; you’re only going to be able to press so hard before you physically can’t anymore, pain ensues, or damage is caused elsewhere. Attempting to achieve a predetermined depth outside ones’ unique articular geometry can cause boney contact and irritation, or compensatory movement in the surrounding joints of the SIJ and lumbar spine. This potentially leads to FAI (femoral acetabular impingement), CAM/pincer lesions (callous formation on the femoral neck/acetabulum due to repeated bone-on-bone compression), or labral pathology. You can’t change your anatomy, and unfortunately, no amount of mobility work will achieve a range of motion outside your joints ability. That being said, few are at the end range of their available hip motion, and hip mobility drills are still advantageous to the majority.
Shakira said it best: “Hip’s don't lie.” It’s important to find an individual set up, based on individual anatomy, which will allow for the most comfortable and unrestricted squatting movement. The most favorable squat stance is the one that allows the best depth while preserving movement integrity. Using multiple approaches, including both active and passive assessments will give good insight into available range of motion and movement capability. Passive range of motion is the available range of motion that can theoretically be used actively.
Consider this test as a screen for optimal squat stance. In a quadruped position, starting with the knees at hip width, rock the hips back towards the heels assessing for a posterior pelvic tilt at the end of the range. Walk the knees out about an inch and reassess, looking for the width that allows the most depth without impingement in the anterior hip and the ability to maintain a neutral spine. Performing this test in an unloaded position eliminates movement insufficiencies that might be found when standing.
Beginning in the previously found stance, use external support to squat down as deep as possible while maintaining neutral lumbopelvic alignment. While at depth, open the feet to a slightly wider position, and alternate turning one foot out at a time to determine the position that provides to most depth without flexing the lumbar spine or creating pain in the front of the hip.
If passive and supported assessments allow squatting without pain or significant limitation, but that range is unable to be attained actively, strength or motor control impairment may be the limiting factor.
There are obviously numerous other factors at play that can restrict squatting range: scar tissue, guarding, soft tissue restrictions in the hip, as well as dysfunctions up and down the chain.
All in all, if you’re built like the Tin Man from The Wizard of Oz, doing some mobility work can help improve overall range, but in some cases, you may be limited to minimal gains. It's important to recognize that prolonged attempts to increase range without improvement may be your anatomic reality. Finding the optimal squat stance and depth is important to avoid boney contact and irritation. If getting your hips below parallel continues to be painful, or unattainable without low back involvement, doing higher squats to a box may be your reality, and that’s okay. Chances are, you outperform that person next to you, that can move like a Cirque De Soleil cast member, in many other movements. Some people’s physiques are designed to perform certain movements, and it takes more dedication, experimentation and modification for others.
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