I am currently going through PT for a pulled quad tendon.
The PT said to only squat down to where my thigh is at a right angle with my calf (4-5 inches above parallel) and not to lock out at the top. This is fine and I’m doing what my PT says to take care of the injury.
However, he also says I should NEVER go lower than this and that I should never lockout even with a 100% healthy knee. His reasoning on depth is that there are some benefits to going parallel, but the risk of knee injury is so much greater that it’s not worth it. On the lock out, it’s that the legs aren’t activated at lockout, so it’s pointless anyway, as well as adding undo stress on the back. Of course, he suggested isolation exercises such as extension, glute, or even squat machines instead.
I should preface this with my experience w/ the PT so far. I find that he actually listens and understands that people are going to do what they are going to do regardless of what he says. He does a decent job at trying to educate me on biomechanics and listening to my body. He comes from a military background (if you count coast guard).
He could be a bit more aggressive on the soft tissue work as well as keeping track of what’s been done. The office as a whole kind of sucks… I’ve had other people’s blood on my table, had techs begin treating the wrong knee, and have seen poor records by other PT’s that filled in for my main PT while on vacation.
From the research I’ve done on this… locking out doesn’t matter so much if you’re not competing, but I’ve never seen anyone say not to hit parallel.