Exercise
June 8, 2011
One of the most widely held exercise beliefs is that you should never let your knees go past your toes when squatting. You’ll hear this “rule” echoed like a mantra over and over by the majority of personal trainers: “Keep the knees behind the toes!”
Fact is, though, there’s little evidence to back up such a claim. It is true that as the knees move anteriorly (i.e. forward) during the squat, the forces acting on the knee joint increase. However, there is no “magic point” where these forces suddenly become dangerous. The plane of the toes has been misguidedly used as a line of demarcation despite a complete lack supporting research. What’s more, intentionally preventing the knees from going past the toes can create additional problems at other joints that are potentially more injuries.
An eloquent study by Andy Fry and colleagues (2003) looked at this very topic. Seven recreationally-trained males performed 3 unrestricted squat lifts and 3 restricted lifts where a wooden board was placed immediately in front of both feet so that the knees were prevented from moving forward past the toes. As expected, knee torque was greater when the knees went past the toes compared to restricted squatting (~150 vs. 117 newton-meters). Sounds like intentionally keeping the knees behind the toes is a good thing, right? Not so fast…
Restricted squats resulted in significantly greater torque at the hip joint compared to unrestricted squatting, with the differences here much greater than those seen at the knee joint (302 vs. 28 newton-meters). Perhaps even more problematic is that results were attributed to a greater forward lean when performing restricted squats. Why is this an issue? Well, in order to squat while keeping knees behind toes, lifters tend to compensate by increasing their forward lean. Studies have shown that an increased forward lean is associated with greater lumbar shear forces. And since the lower back is more susceptible to injury than other joints, this would seem to be a poor tradeoff.
So what’s the take home message? I’ll quote directly from the Fry et al. study as they sum things up very nicely: “While it is critical to protect the knees from unnecessary forces, it is also important to avoid unnecessary forces acting at the hips. These hip forces will ultimately be transferred through the lower back and therefore must be carefully applied. The net result is that proper lifting technique must create the most optimal kinetic environment for all the joints involved. Exercise technique guidelines should not be based primarily on force characteristics for only one involved joint (e.g., knees) while ignoring other anatomical areas (e.g., hips and low back).”
I would note that the same rules do not apply for lunges. Since the lunge involves stepping forward, there is no issue with maintaining an erect posture during performance. The biggest mistake I see is that people tend to push forward on their front leg, which significantly increases shear at the knee joint. Instead, your focus should be centered on dropping the rear leg. In doing so, your front leg will stay perpendicular to the ground, minimizing stresses to the knee joint without negatively impacting the hip or the spine.
Stay Fit!
Brad
Fry AC, Smith JC, Schilling BK. (2003). Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res. 17(4):629-33.
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Nice one again, Brad! You are slaying them one by one (:-
Group fitness instructors are in the same category. I think their manuals specifically tell them to keep their knees not go past their toes. What does NSCA say in their manual? I don’t have my copy with me right now.
Comment by Anoop — June 8, 2011 @ 2:58 pm
Thanks Anoop 🙂 Yes, group fitness tend to be some of the biggest proponents of the no-knees-over-toes theory. I don’t believe the Essentials text mentions this at all (rightly so). It simply describes proper performance.
Brad
Comment by Brad — June 8, 2011 @ 3:52 pm
Great article. probably, the #1 cueing mistake of the squat. ankle mobility, and optimal dorsiflexion are critical to a great squat.
Comment by Dan Daly, CSCS — June 10, 2011 @ 4:10 pm
Great Article.. Hello guys I’m from Brazil and really like to read this articles… I’d like to ask something…
Do you think it’s more important in this cases look at the knee or look first at the ankle mobility? What I think is.. if this guys had started the program with some mobility exercises probably they would squat better than that.. or I’m wrong? Thanks
Comment by André — June 10, 2011 @ 6:52 pm
Hey Dan:
Thanks for the feedback. I agree that poor dorsiflexion is often an issue with proper squat technique. Targeted flexibility training can go a long way to promoting a better squat.
Brad
Comment by Brad — June 10, 2011 @ 7:40 pm
Hey Andre:
As I mentioned in my previous comment, mobility is certainly an important consideration. However, understanding proper technique is equally as important. I wrote a review article for the Journal of Strength and Conditioning Research on the subject. You can read it here: Squatting Kinematics and Kinetics and Their Application to Exercise Performance
Comment by Brad — June 11, 2011 @ 6:45 am
This was a great post. I have struggled with this. I have been told so many times that your knees shouldn’t go over your toes…EVER! So I’ve tried hard to adjust accordingly. However after reading this, I tried a more natural squat where my knees did barely come over my toes and it felt a lot better. Thank you so much for this information!!
Comment by BJN — June 16, 2011 @ 11:53 pm
I’ve first read this study because of an article by Alwin Cosgrove on T-Nation: http://www.t-nation.com/free_online_article/sports_body_training_performance/leg_training_myths_exposed
Comment by Matt — July 17, 2011 @ 9:22 am
This is an awesome, eyeopening article. I always complained that it is physically impossible for me to squat with my knees behind my toes without losing form or hurting my lower back but the instructors at the gym just won’t budge. I then asked him to demonstrate and he too could not do it, especially since the other advice is to keep the toes at a minimum 45 degrees outward angle. Next time the instructor comes to me, I am going to take a print out of this article and show it to him
Comment by Mayuresh — December 6, 2012 @ 3:57 pm
I can’t help but notice a massive flaw in the study you mention. The study compares two squat variations both with a shoulder-width feet placement and a high barbell placement.
Taking a wider stance with more hip abduction wouldn’t cause the butt to go so far back, which would reduce the forward lean.
Using a low-bar placement of the barbell would create a shorter moment arm and reduce the torque at the hip joint.
If you want to compare squat variations, at least compare two properly executed squats to eachother rather than a good squat and a bad squat.
Am I missing something?
Comment by Tobias — September 6, 2015 @ 8:49 am
The question here was whether allowing the knees to go past the toes is detrimental to the joints. If you change kinematics so that the knees don’t go past the toes (by reducing the need for greater compensatory hip flexion), then that’s a different discussion
Comment by Brad — September 6, 2015 @ 9:46 am