We’ve all probably heard an uninformed personal trainer say, “don’t let your knees go past your toes in the squat!” This is bad advice. It’s also one of the most pervasive misconceptions in the world of fitness and it has significant negative effects on the body.
When you restrict the forward motion of the knee and don’t let it pass over the toe in the squat two things happen:
First, is you can’t go as deep. Studies show people can only get down to about parallel when they restrict their knees from passing the toes. Even that depth is only reached if you are very flexible in the hips.
It just so happens that the part of the squat that places the highest compressive force on the knee is at a 90-degree flexion angle where the thigh is parallel to the ground. As you squat lower, the contact between the back of the thigh and the calf reduces the knee-joint forces.
Second, restricted squats in which you keep the knees behind the toes lead to greater flexion at the hip joint (you bend forward more), which puts greater stress on the lower back. This increases risk of injury or pain in the lower back. Keeping the knees from passing the toes in the squat is a key reason more and more people are developing back pain.
Another factor to consider when choosing which kind of squat to do is how the motion affects strength and tissue function in the muscles of the lower body. Allowing the knees to pass forward over the toes in a deep squat motion places the center of pressure closer to the front of the foot compared to when the motion is restricted.
This leads to greater training effect on the plantar flexor muscles of the calf, front of the leg, and ankle, which is key if you want to be able to jump high, run fast, or even walk with ease. For older people, increased strength and function of these muscles will help prevent falls and improve balance.
Full squats also increase the contribution of the quadriceps muscles involved in knee extension, which is necessary for a powerful vertical jump. The quads also play a primary role in sprinting, going up stairs, and other everyday motions. Researchers think this is the reason that full squat training leads to greater improvements in vertical jump height in athletes.
It’s also important to recognize that there are numerous natural motions in everyday life when the knee must pass over the toes:
Every time you walk up or down the stairs, the knees pass over the toes. Try restricting this motion and you’ll notice that it feels incredibly weird, puts a lot of pressure on the hip, and is completely inefficient. Training full squats can help prevent knee pain associated with stairs so that you can navigate them with grace.
Many motions in athletics from pivoting to sprinting to bicycling require the knees to pass the toes, while you are applying force into the ground. Strong and healthy knee and ankle joints are necessary to avoid injury and optimize performance. Training heavy full-range squats can get you where you need to be.
Finally, consider that the athletes with the healthiest knees are those who regularly perform full-range, unrestricted squats in their training:
Weight lifters who perform the clean and snatch and go into a deep squat at the finish of these exercises have a very low rate of knee injury.
Why does allowing the knees to pass the toes during squats lead to healthier knees?
Deep squat training strengthens connective tissue, and something that is known as the “wrapping effect,” which protects the knee. The wrapping effect allows for enhanced distribution of the load over the knee joint.
Deep squats train the brain—muscle connection, building healthy movement patterns that protect you in sports and daily life.
It’s possible that deep squats can reduce inflammation in the knee joint. Inflammatory markers lead to a reduction in synovial fluid, which protects the knee joint. There is evidence that regularly loading the knee with full-range motions can reduce inflammation and improve synovial fluid, which has a therapeutic effect on the knees.
The Bottom Line:
There is no advantage safety-wise to restricting the knee motion of the squat. Doing so may place increased stress on the knee and hip, while putting the lower back at risk. Further, keeping the knees from passing over the toes during squats is less effective for training strength in the muscles surrounding the knee and ankle joints. To optimize lower body strength and power, especially athletic performance, full-range, unrestricted squats are the way to go.
Bloomquist, K., et al. Effect of Range-of-Motion in Heavy Load Squatting on Muscle and Tendon Adaptations. European Journal of Applied Physiology. 2013. Published Ahead of Print.
Campos, M., et al. The geometric curvature of the lumbar spine during restricted and unrestricted squats. Journal of Sports Medicine and Physical Fitness. 2014. Published Ahead of Print.
Chiu, L, et al. Net joint moments and muscle activation in barbell squats without and with restricted anterior leg rotation. Journal of Sports Science. 2017. 35(1), 35-43.
Hartmann, H., et al. Influence of Squatting Depth on Jumping Performance. The Journal of Strength and Conditioning Research. 2012. 26 (12), 3243-61.
Hartmann, H., et al. Analysis of the Load on the Knee Joint and Vertebral Column with Changes in Squatting Depth and weight Load. Sports Medicine. 2013. 43(10), 993-1008.
Lorenzetti, S., Bulay, T., et al. Comparison of the Angles and Corresponding Moment in the Knee and Hip during Restricted and Unrestricted Squats. Journal of Strength and Conditioning Research. 2012. Published Ahead of Print.