We all have heard once or a million times that squats are bad for your knees or that your knees should never go over your toes while squatting. First, squatting is not bad for your knees when done correctly and second, let’s take a closer look. The NSCA (National Strength and Conditioning Association) cites that when squatting the athlete should keep the knees from moving forward over the toes and keep the torso as vertical as possible. Squatters with less skill tend to lean forward and do a “good morning squat”, it is not pretty. Powerlifter tends to use the low bar technique while squatting. This is when you lower the bar on your bar, rather than being on top of the traps it will rest on the high-middle traps and posterior deltoids. Doing this the squatter tends to lean forward more and put more torque on the trunk. No matter how you squat, low or high bar, the maximal torques for the knees is at the bottom position (parallel) of the squat and the maximal torques of the hips is during the second half of the concentric phase (going up).
All that is cool and all, but have you ever thought about how having the knees go over the toes affects the biomechanics of the squat? How would restrict the knees while squatting do to your form? The study “Effect of Knee Position on Hip and Knee Torques During the Barbell Squat” goes over just that. During this study, a group of men, who all high bar squat at least 1.5 times their own body weight to parallel, performed a squat restricting and unrestricting the knees. A board was placed in front of the toes when the restricted squats were performed. To measure joint positions, reflective markers were placed on the base of the 5th metatarsal, the left lateral malleolus, 1 cm superior to the fibular head, the greater trochanter, and the end of the barbell. Each male did 3 restricted and 3 unrestricted squats while being recorded.
The results were significant difference between the two squat conditions (restricted and unrestricted) for torques at both the hips and the knees. “For the unrestricted squat, knee torque was greater than hip torque, while for the restricted squat, knee torque was less than hip torque. The restricted squat resulted in a more vertical shank and a more inclined torso when compared with an unrestricted squat. The restricted squat also exhibited less knee and ankle flexion” (p. 631). The study found that a greater amount of torque was put on the hips and less on the knees while doing restricted squats. This comes from leaning forward more while the knees are restricted. Just like when someone has an ankle mobility if the knees cannot go over the toes, or the ankle properly dorsiflex, the biomechanics of the squat change. Increasing ankle mobility can add a massive amount mobility in your hips (read more).
We all know that it is externally important to protect the knees for unnecessary forces, however, it is also just as important to keep your hips and low back safe. Any force that is put on the hips will ultimately be transferred to the lower back. The goal is to create a squat that is optimal for all the joints involved. No one joint should determine how the exercise technique should be performed and ignore the other joints involved in the lift. The force on the knees become greater as the depth is increased. As the knees move forward over the toes, the shear forces increase. “These shear forces, however, are well below the capacity of a healthy posterior or anterior cruciate ligament” (p. 632). This shows that the velocity of the squat motion is related to the knee shear force. It has also been shown that the low-bar squat can decrease the anterior cruciate ligament strain, patellar compressive force, and shear forces. But do not forget that the forces will happen with either bar position and increase the forward tilt of the torso could increase the forces in the lumbar muscles and ligaments.
In order to have all the joints (ankles, knees, and hips) at optimal force during the squat, it may be beneficial to let the knees move forward over the toes. Remember that at the lowest point of the squat, parallel or below, the knees are able to give the maximal torque. As the hips maximal torques is half way up. Depending on your squat style, having the knee come forward can be beneficial. Just remember to not let the knees go in, stay safe, and get strong!
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Fry, Andrew C., J. Chadwick Smith, and Brian K. Schilling. “Effect of Knee Position on Hip and Knee Torques During the Barbell Squat.” J Strength Cond Res The Journal of Strength and Conditioning Research 17.4 (2003): 629-33. Web. 25 Feb. 2016. <Link>.