"There is simply no other exercise, and certainly no machine, that produces the level of central nervous system activity, improved balance and coordination, skeletal loading and bone density enhancement, muscular stimulation and growth, connective tissue stress and strength, psychological demand and toughness, and overall systemic conditioning than the correctly performed full squat." - Mark Rippetoe
In my eyes the squat is one of the most important exercise - however he is still surrounded by many myths and rumors. The most common ones shall be lied to rest in todays compact article.
1) Knees over toes is bad for the knees, isn't it?
Unfortunately this myth still gets spread by poorly educated trainers, doctors and physiotherapists who don't understand the body's biomechanics (especially of the knee) in context of strength training properly. You simply can't walk a stair up or down without pushing the knees over the toes. Similar to that you cannot squat deep without the toes reaching over the knees. The knee joints only job is to flex and extend over a certain range of motion and if the body allows a particular range of motion, why should you willingly limit it? The result of limiting the range of motion in the knees will always be increased stress on the spines and the hips, which is even worse because the lower back is not designed for excessive forward leans under load.
2) Deep squats harm the knees, don't they?
Healthy knees will never be harmed by a correctly performed deep squat in which the hamstrings cover the calfs completely. Think of the knee gristle as a sponge -> if you compress it in water it will soak itself after the compression is over. Something similar happens to the knee gristle, as it is supplied with nutrients after compressive stress. So in fact, if the joint is not exposed to compressive stress in specific range of motions it is more prone to injuries and degeneration. A phenomena that can be observed in the sedentary population where joint and bone degeneration is a common aging problem. [Deep squats don't harm the joints, but not squatting at all does!]
3) But heavy weights must harm the knees?
If you expose yourself to heavy weights within an intelligently designed and progressively overloaded strength program, there will be absolutely no harmful stress on the knees. There is a reason why olympic weightlifting is actually one of the sports with the lowest! rate of knee injuries and injuries overall unlike sports such as soccer (most soccers don't squat unfortunately...).
To be continued [...]