I was giving a two-day seminar to a group of 15 personal trainers on powerlifting technique. When we started the squat module, I asked “how many people think squatting with your knees passed your toes is dangerous”? Everyone by one person raised their hand.
So can the knees pass the toes safely and effectively when squatting? The knees bending in front of the toes can be performed safely and effectively if a person doesn’t have any injuries, and can keep their knees stable/balanced. To keep the knees stable/balanced you must, first, keep them in line with your foot (not caving inward), and second, ensure the bar is directly over the mid-line of the foot at the bottom of the squat.
Let’s dive deeper into the mechanics of the squat to see how much stress gets put on the knees when they travel forward. We’ll also discuss how you should set-up and initiate the squat to ensure a safe and effective position with your knees.
But First, Where Did This “Myth” Come From?
The “don’t let your knees pass your toes” myth started from a 1978 study that showed maintaining a more vertical shin position, when the knees don’t pass the toes, reduce shear forces on the knee when squatting.
I want to explain what shear force is. I promise I’ll bridge this nerdy physics stuff into practical application in the next section.
Shear forces are unaligned forces pushing one part of the body in one direction, and another part of the body in the opposite direction. When contracting the quads, the kneecap gets pulled on due to the femur (leg bone) shifting backward, and the tibia (shin bone) shifting forward. This causes the kneecap to move away from the tibia.
This is shear force at its finest.
But there’s one more thing to know: shear forces increase when the joint moves further away from the load.
As an example, when you’re standing with the barbell on your back, the load is directly over your hips and knees. It’s in alignment and there’s not much shear force happening here. As you squat though, your knees move in front of the load (the barbell), creating a horizontal distance between the load and knees, which is where the shear force described above occurs.
The further the knee travels forward, the greater the horizontal distance between the knees and load, and the more shear force. Keep your knees back, more in line with the barbell, less shear force.
So with the result of the 1978 study showing that shear forces can decrease if you can keep your knees behind your toes, fitness professionals started to advise their clients to squat in this way. This makes sense because fitness instructors work with everyday people (not athletes) and they err on the side of caution — as they should.
But the study failed to account for one thing…
Squatting is a Multi-Joint Movement
The 1978 study failed to address other forces acting on the body, especially through the hips.
A study in 2001 confirmed that shear force increased by 28% when the knees were allowed to move in front of the toes while squatting. However, the shear force increased at the hip by nearly 1000% when subjects were restricted in moving the knee forward in the squat.
The same principles above apply with the hips but in reverse.
Instead of the knees traveling forward, the hips are now traveling backward. If you want to prevent the knees from going over the toes, the hips need to travel quite far behind the load. You can think of this type of squatting as really trying to push your hips back as you descend into the squat, putting the majority of the load onto your heels.
So what should we take away from this?
Squatting is a multi-joint movement and we’re going to experience some level of shear force at the knee and hip as we descend into the bottom range of motion. There is a give and take relationship between the hip and the knee. As the knee limits its range of motion forward, the hips increase its range of motion backward, and vice versa.
So the cue to limit the knees from moving forward only works to a point. If you want to do a full range squat, you will need to push the knees forward in front of the toes eventually. The deeper the squat, the more your knees will need to move forward to remain balanced, and prevent excessive shear force at the hip.
Let’s talk about the right balance between pushing the knees forward and pushing the hips back in the squat.
The knees are going to be further far forward in the back squat compared with the box squat. Learn more differences between the back squat vs box squat.
It All Starts With How You Initiate The Squat
What To Do & What Not To Do
The best way to start the squat is by hinging at the hips before bending at the knee.
You don’t want to over-exaggerate the hinging, but you do want to feel like there’s some forward lean and bending at the hip before cracking the knees. This will load up your posterior chain (glutes, hamstrings, erector spinae) and keep the bar over your base of support (the mid-line of the foot).
Let’s consider the opposite — bending at the knees first.
Eventually, you will come to a point halfway down where your ankles will restrict you from going any further. At that point, you will need to push your hips back rapidly to compensate for this restriction. This is not the point in the squat where you want to make any rapid changes to your hip position, especially under load (a big squat mistake).
In addition, your balance and efficiency are judged by how well you can keep the load over your base of support. When you bend the knees first the load automatically goes forward onto the ball of the foot, which is less stable and harder to control.
Related Article: 5 Best Squat Shoes For Knee Pain
Cue Hips, Then Knees
So the squat should be initiated by the hips first. A good cue is to think about ‘cracking the hips’, and ‘loading the feet’. This allows you to load the posterior chain, and feel your base of support through your feet.
Regardless of your individual mechanics, everyone will need to have some forward knee bend.
So at about halfway down, you’ll want to start pushing forward into the knees to move the hips underneath the torso.
Remember, the deeper you squat, the more forward knee bend is required. This is normal.
What To Look For In Terms Of Safety
At the bottom of the squat you’re looking for a few key positions in order for the movement to be considered safe on the knees:
- Are the heels flat on the floor?
- Are the knees caving inward?
- Is the bar over the mid-part of the foot at the bottom?
So rather than being concerned about whether your knees are going in front of the toes. Look for each of these positions. If they aren’t achieved, then you’ll experience more sheer force at the level of the knee joint above and beyond what’s considered ”normal”, and you’ll feel less stable while squatting.
Individual Mechanics: How Much Forward Knee Bend Should You Have?
How much forward knee bend is going to vary drastically from person to person based on the length of their tibia (shin bone), femur (thigh bone), and torso.
Someone who has longer femurs (and shorter tibias), will need to push their knees forward more if they want to squat full range of motion. Conversely, someone who has shorter femurs (and longer tibias), will be able to sink their hips into a deep squat without having to push their knees forward as much.
The best explanation of how to treat your individual mechanics while squatting is by Tom Purvis. What you should take away is that there’s going to be biological strengths and limitations with how you’re built. It’s not whether the knees will travel in front of the toes, it’s when they do travel in front of the toes, the distance traveled is a result of how you’re built.
If you play a sport, there will be several moments where the knee is required to travel forward past the toes. Therefore your strength training program needs to take your performance goals into consideration and prepare the muscles and joints to handle the applicable forces.
This is true whether you’re a powerlifter, football player, speed skater, or otherwise. However, if you’re someone who works out to lose weight and has general health goals, then your training requirements may not require you to squat as deep, and as a result, not have excessive forward knee bend. You need to decide which category you fit into, and assess whether doing deep squats will be beneficial for your goals.
For example, you can read my article on the Olympic squat vs powerlifting squat, where I describe that it’s more beneficial for Olympic weightlifters to have their knees bent further forward in the squat.
Rather than focusing on how much the knees push in front of the toes, think about keeping the bar over the midline of the foot, the heels on the ground, and prevent the knees from caving inward. To help achieve this, start the squat by ‘cracking at the hips’ to load the posterior chain, and then bend the knee forward as you get deeper into the bottom.
What to Read Next?
- McLaughlin, T., Lardner, T., & Dillman, C. (1978, May). Kinetics of the parallel squat. Research Quarterly, 49(2), 175-189.
- Fry, AC., Smith, JC, S., & Schilling, BK. (2003, November). Effect of knee position on hip and knee torques during the barbell squat. Journal Of Strength And Conditioning Research / National Strength & Conditioning Association, 17(4), 629-633.