Time to read: 4 min
“Don’t let your knees go over your toes”, “keep your knees behind your toes” are cues you may have heard before.
When asked why, the person giving the cue, may say it is safer for your knees; they’re not wrong, when the knees move forward during the squat the force placed on your knees does increase.
So, do we allow our knees to go over our toes or not?
Fry et al, 2003 performed a study on this exact question “Effect of Knee Position on Hip and Knee Torques During the Barbell Squat”.
7 trained males performed 3 restricted barbell back squats (a wooden board placed in front of their feet, image B below) and 3 unrestricted barbell back squats (image A) and forces (torque) were measured (newton meters (N.m)) at the knee and hip joint.
|Results||Unrestricted (A)||Restricted (B)|
|Knee||150 ± 50.8 (N.m)||117.3 ± 34.2 (N.m)|
|Hip||28.2 ± 65.0 (N.m)||302.7 ± 71.2 (N.m)|
As you can see, there is less force on the knee when kept behind the toes however at the expense of significant forces at the hip/back. As such it’s a poor trade-off to slightly reduce knee forces while significantly increasing hip/back forces.
When restricted (B) knee-at-toe, there is much more forward lean to compensate for the restriction at the knee/ankles. This places a significant amount of shearing force at the hip joint and lumbar spine.
The squat is a multi-joint movement and exercise technique should consider all joints in the movement, not a single joint in isolation.
To quote the study:
“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”
Take home: Knees over toes is expected during descent and can optimise forces at all joints involved.
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.