The squat is one of the most fundamental movements a human being can perform. But I get asked constantly by patients if its OK to do squats, and I usually hear them say "someone told me it was bad for my (insert body part here)." 'Who is this someone, and how do they know so much about squats?' I always wonder. How would anyone stand up from a chair if not for performing a (fairly deep) squatting motion? How come no one ever said sitting to standing was dangerous?
The only universal truth about exercise is that everyone should do it, so I don't want to come out and say that there is a specific type of squatting workout that's best. Further, pathology or injury will certainly change the approach, and there are certain acute conditions with specific restrictions, such as surgery. But the good news is for the majority of people, squatting is a safe and essential part of an exercise and recovery program. Make sure to talk to a Physical Therapist or qualified personal trainer (with NSCA or ACSM credentials, or bachelors/masters degree) if you are beginning a program including squats - or any complex, unfamiliar movement, as the nuances can make all the difference in performing it correctly.
One size squat does not fit all. Squatting down to the floor with 300 pounds on your back is insanely different than bending your knees and pushing your hips back while holding onto something for support. Clearly we are much more likely to get hurt doing the former, and this is where a majority of the injury myths stem from. Most squats are somewhere in between these two extremes. My 80 year old patients with knee arthritis are not doing loaded (with weight) squats, but they are definitely doing mini-squats with upper body support, or some variation of sit to stand movement from a high bench or treatment table until they can progress something more difficult. If you are currently dealing with an injury or pain and are wondering if you should or could squat, start with a short depth and low total reps and assess your tolerance. If this type of simple squat bothers your knees, there is a good chance you're doing something wrong, or have underlying pathology that should be addressed. Either way, its time to make an appointment with a PT!
Myth #1 : (Deep) Squats are bad for my knees
It might be hard to believe, but there is exactly ZERO evidence that squats cause degenerative knee pain. Saying squats cause knee pain is like saying walking causes foot pain. How much walking are you doing? Are you overweight, or wearing bad footwear? There are a lot of factors that must be considered, and eliminating overtraining or training with poor mechanics often eliminates any issues with any specific movement. Bottom line here is that poor technique or inappropriate exercise prescription can lead to injury, but with good form the squat is an extremely safe exercise.
Myth #2: If I have a bad back, I shouldn't squat
Actually, training the squat appropriately will teach us to use our hip muscles and lower leg to bend down, instead of folding at the lumbar spine. Both increased lumbar flexion or extension leads to higher compressive forces, so maintaining a neutral pelvis is of utmost importance for those with any back issues or concerns. To find pelvic neutral, feel the amount of movement you can tilt your pelvis forward and backward. Choose a position that allows you to move the same amount of distance into anterior tilt as posterior tilt. This position should be the "middle" of the available ROM of the pelvis, thus 'pelvic neutral'. For those who are experienced lifters, loading with a front squat will decrease compressive forces on the spine as opposed to a back squat.
Myth #3: Your knees shouldn't go passed your toes
I saved my favorite one for last. There are a few theories as to where this myth came from, one being from a study from the University of Memphis where they either limited the forward movement of the knees with a board placed at the toes, or let the participant squat unrestricted. The research found a 22% increase in shear forces at the knee with the unrestricted squat, but also a 1000% (!) increase in torque at the hips. This minimal increase in shear force was mistakenly interpreted as dangerous, even though it has been demonstrated to be well within the capability of the knee structures to withstand this amount of force. Further, with the disproportionate amount of loading placed on the hips, it stands to reason that a more even distribution of forces as would be seen in the unrestricted squat would be more appropriate, especially when the movement is loaded.
(image from squatuniversity.com)
The other basis of the myth likely came from simplifying the verbal cuing of the movement during exercise classes or instructors who had limited time to teach the movement. A common mistake when performing the squat is to bend only at the knees, keeping the hips from moving and therefore putting maximal shear on the knee, and moving the center of mass over the toes. Moving this way is not the same as squatting, but it is a super common error and is a non-optimal pattern of movement. Using the cue "don't let the knees go passed the toes" to combat this tendency makes sense, since to get lower into the squat and remain balanced, one would need more movement from either the hips or the back. If the client performed inappropriate lumbar flexion, then likely the addition of "keep your back straight" would have corrected that compensation, and allowed for two simple cues to give a decent approximation of a good quality squat. When being taught in a more individualized setting, however, these simplifications become unnecessary, and therefore should be avoided in order to avoid confusion especially with those new to learning the movement.
Fry, AC., Smith, JC, S., & Schilling, BK. (2003, November). Effect of knee position on hip and knee torques during the barbell squat. Journal Of Strength And Conditioning Research / National Strength & Conditioning Association, 17(4), 629-633.