>>648219Descending is a bitch on the knees, expecially if you're overweight and/or tall and/or not physically fit.
If your pain is localized under the rotula, in the front part of the knee it might be due to a weak quadricep muscle, during the descent the muscle isn't strong enough to hold the leg and you'll put more strain on the knee and the patellar tendon suffers (
https://en.wikipedia.org/wiki/Patellar_tendinitis).
Visit a doctor, if you have an inflammatory process going on stop hiking, no weight training, exercise only in a swimming pool (you can do proper leg training without having to deal with gravity), do not under any circumstances force the pain since you might end up damaging permanently your tendons, or even rupturing them and you'll be fucked.
Also use trekking poles with the proper techniques, expecially if you're carrying a backpack.
Source: I've had patellar tendinitis, achilles tendinitis, various shit.
Take care, hiking is not an activity which should be taken lightly.
