If you've spent time in any gym, you've likely heard the well-intentioned advice: "don't let your knees go over your toes" when squatting or lunging. This coaching cue has been ingrained in fitness culture for decades, often repeated without question or clear understanding of its origins. But where does this advice actually come from, and is forward knee travel truly detrimental to your knee health?
This article examines the science behind this specific area of squat mechanics and challenges this persistent myth while providing clarity on when this restriction might actually be warranted. Whether you're a trainer, coach, or someone who simply loves to squat, understanding the biomechanical principles discussed here will revolutionize how you approach this fundamental movement. We also have an interactive simulation for you to experiment with, helping you visualize exactly how different limb proportions impact your individual mechanics, including whether you are more likely to have your knees naturally translate forward during your squat.
"Knees Over Toes": More Complex Of An Issue Than It Sounds
Before diving into the research, we need to clarify what "knees over toes" actually means, as this phenomenon exists on a spectrum and can occur for several different reasons. Some instances of forward knee travel are completely natural to a person's movement patterns based on their anatomical proportions, while others may result from technical errors or compensations from mobility limitations. The conventional coaching cue against forward knee travel has surprisingly vague reasoning in most circles and remains poorly understood by many coaches who use it regularly.
At one end of the spectrum, you have natural, proportionally-driven knee movement that occurs as part of optimal squat mechanics. At the other end, you have excessive forward knee displacement that may indicate mobility restrictions, stability issues, or technical flaws in the exercise. The blanket prohibition against any forward knee travel fails to distinguish between these vastly different scenarios, often creating an oversimplified approach to teaching the movement and in some cases it causes more problems than it solves.
Contrary to popular belief, allowing the knees to travel forward isn't inherently "bad" for knee health. In fact, the idea that knees traveling past the toes in healthy individuals is harmful lacks solid foundation in scientific literature, despite decades of this coaching cue being perpetuated in gyms worldwide. The human knee is remarkably well-designed to handle forces in multiple directions, including those that occur during natural forward knee movement when the movement is controlled and stable.
What the Research Actually Shows
Scientific inquiry has consistently challenged the notion that anterior knee displacement is inherently dangerous. A study by Fry et al. (2003) investigated the biomechanical implications of restricting knee travel during squats. When participants were instructed to squat without their knees going over their toes, the researchers found that knee torque decreased while hip torque increased significantly. At first glance, this reduction in knee torque might seem to support the traditional coaching cue, suggesting significant protection for the knee joint.
However, the researchers identified a critical concern that is over looked if we take the numbers at face value: Where do the forces go when forward knee movement is artificially restricted? The forces don't simply disappear—they shift elsewhere in the kinetic chain. Their discussion revealed that excessive forward lean and posteriorly displaced hips, both potential consequences of the "knees behind toes" restriction, may inappropriately load the lower back and create significantly higher shear forces on the lumbar spine. This would be particularly problematic in individuals who squat with otherwise good form but whose body proportions naturally lead to more forward movement of the knee over the toes like those with shorter femurs.
The study's findings suggest that while total knee torque may decrease by instructing people to prevent their knees from coming forward, forcing this position unnaturally may create more problematic loading patterns elsewhere in the kinetic chain. The normal torque experienced by a healthy knee during natural squatting movement does not appear to be problematic or harmful, as the knee joint is robustly designed to manage significant forces when movement is controlled and stable.
More recent research by Illmeier and Rechberger (2023) echoed these findings while making an even stronger case for natural movement patterns. Their comprehensive review provides this summary statement:
"For a large number of athletes, it may be favorable or even necessary to allow a certain degree of anterior knee displacement in order to achieve optimal training outcomes and minimize the biomechanical stress imparted on the lumbar spine and hip."
Both studies converge on a crucial principle that challenges decades of conventional wisdom: individuals should squat in a way that naturally balances forces between the knees and hips, respecting their unique body proportions rather than conforming to largely arbitrary restrictions. This approach not only optimizes performance but also reduces the risk of compensatory movement patterns that can lead to injury in other areas of the body. While our goal here with this article is more to describe the findings in plain language, both studies are cited in our references and you may read them yourself if you’d like to see the statistics.
Bar Position: Another Important Piece of the Puzzle
One critical factor often overlooked in coaching this movement is how bar placement dramatically affects the mechanics of the squat. This oversight can lead to a significant mismatch between cueing and the desired movement outcome, potentially forcing athletes into biomechanically disadvantageous positions. The fundamental principle guiding barbell squats is to keep the bar positioned over your mid-foot throughout the entire range of motion, ensuring the load remains over your body's center of mass.
High Bar and Front Squats
When the bar sits across the upper traps (high bar position) for a back squat or in the front rack position for a front squat, the load's proximity to your center of mass naturally promotes a more upright torso and a more strictly vertical bar path. In these variations, the knees typically need to travel further forward to allow the hips to drop straight down while keeping the bar over the mid-foot. The closer the weight is to your center of gravity, the less your body needs to compensate with extreme positioning to maintain balance and stability.
Restricting knee travel when the bar is in either of these positions forces the hips unnaturally backward relative to the load placement, moving the bar away from your center of mass and dramatically increasing stress on the torso and lower back. This creates a biomechanical disadvantage that can lead to technique breakdown and potential strain on the low back. This error is fairly common with new coaches and trainers as well as individuals new to the barbell squat who apply universal cues without considering load placement.
If you are learning or coaching a high bar or front squat, be aware that the typical movement path is more strictly vertical, meaning that while the hips do move backward, it's not as pronounced of a hip hinge as you would see with a low bar squat. The knees naturally travel forward to maintain the center of mass under the bar, and this should be embraced rather than restricted so long as there are no orthopedic reasons to avoid this positioning.
Low Bar Squats
On the other hand, low bar placement (where the bar rests slightly lower on the back, across the rear deltoids) naturally accommodates a more pronounced hip hinge and a steeper trunk angle, which is more conducive to keeping the knees behind the toes or closer to the line of the toes. This isn't because it's the "only right way" to squat, but because the lower bar position shifts the center of gravity backward, necessitating greater hip hinge to maintain balance and prevent the weight from pulling you forward.
The low bar position requires this pattern of movement to maintain the load over your center of mass. In this variation, restricting forward knee travel aligns with the natural mechanics required by the bar position, making it a more appropriate application of the traditional cue.
Bar position is extremely important to consider when you are assessing either your own squat mechanics or those of a client or athlete. We need to ensure that we aren't accidentally forcing an unnatural position that could adversely load the low back and spine by applying inappropriate cues for the chosen squat variation.
Individual Anatomy: Why One Size Doesn't Fit All
Beyond bar position, individual anatomical variations play a role in determining optimal squat mechanics. Just as no two people have identical fingerprints, no two people will squat exactly alike, even with perfect form.
Limb Length Ratios Matter
While most people's squat mechanics will share fundamental similarities, individual factors like your femur-to-tibia ratio significantly influence optimal squat mechanics and should guide technical coaching decisions.
Individuals with longer femurs relative to their tibias and torso naturally require more hip hinge and a steeper torso angle to keep the bar over their mid-foot or just to be balanced during a body weight squat. These individuals may find low bar positioning more comfortable and mechanically efficient to accommodate their anatomy. Their proportions necessitate greater backward hip displacement to maintain balance, making excessive forward knee travel less natural.
Individuals with relatively shorter femurs and longer tibias naturally accommodate a more upright positioning with more potential for forward knee travel. Their proportions allow for a more vertical squat pattern without compromising balance or creating excessive stress on any single joint.
When "Knees Over Toes" IS Actually Problematic
While forward knee travel is generally acceptable and necessary in some body types, there are specific scenarios where the traditional cue becomes relevant and should be applied, even in individuals with normal, healthy knees. The key is understanding that the problematic aspect isn't the anterior knee displacement itself, but rather the underlying dysfunction or instability it may reveal.
Compromised Stability and Base of Support
The primary concern arises when stability is compromised. If your heels lift during the squat and your weight shifts toward your toes, then your knees are pushed forward well beyond your base of support as a result which creates an unstable position that's genuinely problematic. This pattern typically indicates significant ankle dorsiflexion mobility limitations but it does place significantly more stress on even healthy knees while creating an unstable base of support.
When the knees travel excessively forward due to compensatory patterns, several issues can arise. First, the base of support becomes compromised, leading to balance issues and potential safety concerns especially when squatting with some kind of resistance. Second, the forces acting on the knee joint become less favorable, potentially increasing stress on the patellar tendon and other knee structures. Third, this pattern often indicates underlying mobility restrictions that need to be addressed for optimal long-term joint health.
That said, many people struggle to maintain completely flat heels while squatting, and this is something to work on progressively rather than something that should prevent you from squatting entirely. While working with your trainer or actively working on your ankle mobility, try squatting with a small weight plate or heel wedge under your heels. This extra bit of elevation allows you to squat deeper in a similar way as you would with unrestricted ankle mobility.
However, don't fall into the comfortable trap of always squatting with elevated heels just to mask the underlying mobility problem. Address your ankle mobility limitations through targeted stretching, soft tissue work, and mobility exercises. That said, elevated heels are also a legitimate technique for achieving greater range of motion and can be used strategically even by those with good ankle mobility, but the effect will be further amplified if you have unrestricted ankle movement.
Uncontrolled Lateral Movement
Another genuinely problematic scenario occurs when the knees travel excessively forward and simultaneously collapse inward (knee valgus) or outward (knee varus). While some degree of knee valgus under heavy loads may be normal in elite lifters, significant and uncontrolled collapse indicates instability, often due to weakness in the hip abductors or glutes, or poor motor control. This uncontrolled movement pattern, especially when combined with significant forward knee travel, can place undue stress on the knee ligaments and menisci, increasing the risk of injury. The issue here isn't just the forward movement, but the lack of stability and control in the frontal plane. We can address this in a future article because unstable hips cause all kinds of upstream (back pain) and downstream (knee and ankle pain) issues.
Pain as an Indicator
Ultimately, if allowing your knees to travel forward, even in a seemingly biomechanically sound way, consistently causes pain in your knees or surrounding joints, then for your individual body, it is problematic. Pain is a clear signal that something is amiss and should prompt an assessment by a qualified professional to identify the root cause, whether it's a mobility issue, strength imbalance, or a pre-existing condition that requires modification of your movement patterns.
How Should My Squat Look for My Proportions?
After reading through this article, are you wondering what your squat mechanics should look like based on your individual proportions? Test out the simulation embedded below and adjust the fields to try and match something similar to your own measurements. Are you squatting correctly for your unique anatomy?
Press 'Play' first, and then you can adjust the limbs in real-time to see how factors like femur length, tibia length, and torso length affect your optimal mechanics. Here are a few things to experiment with:
Practical Applications for Coaches and Gym Goers
Understanding the science behind knee travel should fundamentally change how we approach squat coaching and training.
For Coaches:
Begin by assessing individual proportions before applying any universal cues to your athletes. Take time to observe their natural movement patterns and identify whether forward knee travel is occurring due to anatomical necessity or compensatory patterns. Match bar position recommendations to natural movement patterns rather than forcing all athletes into the same squat variation. An athlete with longer femurs may thrive with a low bar squat, while someone with relatively shorter femurs might perform better with a high bar or front squat variation.
Address mobility limitations systematically rather than simply restricting movement. If an athlete's knees travel forward excessively due to ankle mobility restrictions, work on improving ankle dorsiflexion rather than just telling them to keep their knees back. Focus on teaching stability and control throughout the entire range of motion, ensuring that any forward knee travel is part of a stable, coordinated movement pattern, not an uncontrolled collapse.
Educate your athletes about the reasoning behind your coaching decisions. When they understand why certain positions are recommended for their individual anatomy, they're more likely to embrace the coaching and make lasting improvements.
For Gym Goers:
Experiment with different bar positions and stances to find what feels most natural and allows for the best expression of strength and mobility. Don't force yourself into unnatural positions simply to match what you see others doing in the gym. If a certain squat style feels consistently awkward or painful, it might not be the right fit for you.
Prioritize consistent technique that respects your individual anatomy over adherence to universal cues that may not apply to your body type. Focus on maintaining a stable base of support, controlling the descent, and driving through your mid-foot and heels while allowing your knees to move naturally. Develop a repeatable, controlled squat pattern that feels strong and stable, regardless of how far your knees travel so long as you are able to keep your feet flat on the floor while doing it.
Perform regular self-assessment to evaluate your ankle mobility and address any restrictions that might be forcing compensatory movement patterns. Simple tests like the wall ankle mobility test can help you identify whether mobility limitations are affecting your squat mechanics (articles about this coming soon).
The Bottom Line
The scientific evidence consistently demonstrates that the traditional "knees behind toes" coaching cue is not only largely unsupported by research but may lead to inappropriate loading of the hip and lumbar spine in certain individuals. Allowing natural anterior knee displacement during squatting is biomechanically sound and functionally necessary for many people based on their individual anatomy.
The persistence of this myth in coaching and fitness communities represents a significant disconnect between scientific evidence and practical application. This gap has led to countless individuals being coached into suboptimal movement patterns that may limit their performance and potentially increase their risk of injury in other areas of the body as mentioned with the low back.
As the strength and conditioning field continues to evolve toward evidence-based practice, it is crucial that individuals—both professional and recreational—embrace current understanding of squat biomechanics and abandon outdated restrictions that may limit performance and lead to unnecessary strain. The future of effective coaching lies in individualized assessment and programming that respects anatomical variations rather than forcing conformity to arbitrary standards.
The "knees-over-toes" restriction creates an unnecessary limitation in most cases with healthy knees and should be considered antiquated. Instead, it should be replaced by individualized, evidence-based coaching that prioritizes thorough movement assessment, optimal movement quality, and deep respect for individual anthropometric variations. This approach not only optimizes performance but also promotes long-term joint health and movement sustainability.
By understanding and applying these principles, we can move beyond outdated myths and embrace a more scientific, individualized approach to learning and coaching one of the most fundamental human movements. The result will be better performance, reduced injury risk, and a deeper appreciation for the remarkable adaptability of human movement patterns.
References:
Fry, A.C., Smith, J.C., & Schilling, B.K. (2003). Effect of knee position on hip and knee torques during the barbell squat. Journal of Strength and Conditioning Research, 17(4), 629-633.
Illmeier, G., & Rechberger, J.S. (2023). The limitations of anterior knee displacement during different barbell squat techniques: a comprehensive review. Journal of Clinical Medicine, 12(9), 3264.
