It would take me hours to count the number of times I've heard it said that you shouldn't do squats for different reasons. In general, they say that it damages or negatively affects the spine and/or knees, but it really is one of the most fundamental movements of human beings. It's no joke that in many countries, there are people who rest in a squatting position, instead of sitting on a chair.
However, it never hurts to be aware of studies and information that attempt to arrive at the best hypothesis. It's true that knee injuries are among the most common, so it's important to understand how squat positions affect the knee. A study published in the Journal of Strength and Conditioning addressed this issue.
What pressure is exerted on the patellofemoral joint?
Although it might seem like an unusual term for a joint, anatomically we're referring to the structure that rests on your knee. Injuries to this joint account for approximately 30% of all knee injuries , and the pressure exerted on it appears to play a significant role.
The researchers analyzed different weights and joint angles during squats, and studied how they affected the forces on the knee. They observed that maximum force decreases as squat depth increases. So they tested the maximums of the volunteers in the three different depths of squats.
The scientists hypothesized that the forces on the knee would grow as the squat deepened; but reducing the maximum weight in the lowest position would reduce the force evenly.
Knee strength increased with heavier weights and deeper squats. And, even though the maximum repetitions were lower in the deepest position, the force at the knee was still the highest. Even so, we must take into account that the shape and leverage of each person are different, so it is not possible to generalize with these results.
Athletes without injuries vs. with injuries
Athletes who have never suffered a knee injury should keep a few important points in mind. Many people perform heavy squats to great depths for years without any problems. In fact, researchers have noted that experienced weightlifters have reduced knee laxity , resulting in healthier soft tissues in their joints compared to sedentary individuals.
However, for people with knee injuries or pain , it's best to start with unloaded squats above parallel. Over time, you can slowly increase the depth before adding weight.