Howdy,
Patellofemoral pain syndrome (PFPS) is a dull, aching pain around or under the kneecap that worsens when you use stairs, squat, run, or sit with bent knees for a long time…
Squats had lower patellofemoral joint (PFJ) stress than knee extensions at 0°-30°, but higher PFJ stress than knee extensions at 60°-90° (Powers et al 2014).
Shallow squats are safer in the beginning of rehab, as well as deeper knee extensions. But, it always depends on many factors (where the cartilage is damaged if that’s the case; pain tolerance, individual knee-complex anatomy…).
PFJ loading ranged from 0.6 x body weight in walking up to 8.2 x body weight in a single-leg decline squat, and the highest tier was made up of challenging squat variations, not some evil knee extension machine (Song et al 2023).
So, be careful about squatting variations! And, don’t be afraid of walking and running (being active in a safe manner is very useful). Train/rehab smart!!!
Last but not least, whatever you’re doing, it’s important not to awake pain that much, which you can do by finding “non-painful” angle/range, and build up your strength within that range – till the capacity increases so you can also change that range little by little. Nice and smart progression is key!
Yours in progression,
Luka