Okay haha. From my experience, I have heard absolutely horrific advice from martial artists over the years when asked exercise or injury advice. There are so many old school practices that are just practiced because it was the way their instructor taught them. Excessive bunny hops prior to students being physically conditioned to do them, being told to "stretch" if they're injured (if a tendon is partially torn, stretching is one of the worst things you can do and will tear it further)... etc etc. So I rarely ask for exercise or injury advice from martial artists unless I know they are knowledgeable on the subject.
But anyway. My right knee started playing up and getting more painful a couple of years ago. I actually feel it was due to excessive repetitions of all our kihon/kicks, so a combination of overuse, imbalance, excess tension and possibly wear and tear but unsure.
Being the avid psycho researcher haha, I looked into a few avenues, and three main things which I feel helped immensely:
1) Correcting imbalances by strengthening and prioritising other important muscle groups: glutes, hamstrings both at hip extension and knee flexion function, calves, and tibialis anterior which is often neglected. Often knee pain is a result of things occurring at the hips or the feet or both. Strengthening things through the chain and aiming for more balance gives the knee more support. We are often way too quad dominant, especially in martial arts, so strengthening other muscle groups allows the quads/knees to not overcompensate and take on too much of the load.
2) strengthening the musculature around the kneecap (particularly the VMO muscle) which was still necessary. Here I will differ from a previous post hehe
, exercises like the ones from kneesovertoesguy were incredibly helpful (and insane amounts of people have gotten crazy results), BUT you have to build up progressively to the deep deep knee bend stuff. Take a very long term approach and don't skip steps. Becoming stronger in those end range positions (which we are weakest in the end ROM) really helps develop resilience when we happen to go into those positions naturally. Starting small like peterson stepdowns (which is the motion we do walking down stairs anyway) and building from there. I can now do full range reverse nordic curls (no band assistance) which would have been impossible years ago.
3) other advice I was given was to introduce movement variability, as in try something new, a different exercise that challenges things differently. I took up running and what I call "free play" haha, a mix of trail running and parkour where I'm exploring the terrain in a fun, playful way. Often jumping, going side to side, balancing on things, it's a lot of fun. And also when running striking mid-foot/ball of foot, NOT heel striking has really made a difference.
Other things like stretching and massage are important, but moreso mobility which develops strength through the range of motion rather than just passive flexibility.
My knee is the best it's ever been. Still gets a little sore every now and then, but not often. So being very mindful how I practice martial arts and getting my stances and kicks correct is always a focus.
But it's important to figure out what would be causing your knee pain. Often it can be not due to the knee itself but something else down the chain that needs addressing. Hope this made sense haha.