@golvmopp you know anatomy and all that.. you ever deal with issues with the back of your knee? After lifting heavy then running and walking right after, I developed pain in the two tendons right at the back of the knee. Walking is somewhat uncomfortable but not a problem and I was skiing fine. But today I tried leg curls and it really aggravated those two tendons so I stopped. You know what that may be? It is now about 1.5 weeks since it first came along.
Wall of text, but here goes. Cant tell what the issue is, but I'll give you a self-assessment starter kit.
First off, map the location of the pain. Go full autismo on an image search engine, start with general search terms and progress to more specialized queries as you go on - i.e. start with "back of knee anatomy", plot the origins and insertions of all relevant muscles you see in multiple results from the first search. Start using separate image searches, like "soleus insertion origin", "semitendinosus insertion origin" etc. Refer to multiple images so you may gain a complete 3D understanding of each individual muscle, how they overlap, how they function and across which range of motion of the joint they are the most active. Dont neglect the importance of lesser known muscles, so spend the time to acquaint yourself with as many muscles as you can in the area you're plotting.
Good! Now you're getting an understanding of the muscular make-up of your body. The question you need to ask yourself when self-assessing however, is whether your issue is muscular, joint- or nerve-related. Some locations have a higher chance of the latter two options, and many issues are caused by remote dysfuntions from other areas of the body.
One example would be an underactive right glute causing left lumbar pain due to the left lumbar compensating for the right glute.
Another would be a tight piriformis muscle impinging on the sciatic nerve, which could be felt as lower back pain, or pain shooting down the leg when doing anything that involves activating the piriformis.
The more you learn about joint kinematics ("... the study of the relative motion between two consecutive segments of the human body" according to some site), the easier you'll be able to diagnose what's wrong with you, because you'll both learn how the function of certain muscles change as a joint moves across its range of motion. More importantly, you'll start self-assessing on the go by recalling all the info you just crammed into your head from the previous steps - "oh shit, x muscle feels tight when doing this which probably means that my posture is crap or that I'm not bracing with y muscle properly" etc.
If you're lucky, it's a local muscular issue. Otherwise you'll have to run the gamut, but you'll learn A LOT over time on how to self-sustain a healthy physique.
If it turns out to be joint- or nerve-related, you're gonna have to apply the same amount of autism on skeletal and/or neural anatomy. Keep in mind that issues can occur across these structures, i.e. tight muscles can lead to faulty joint kinematics, which can lead to nerve impingement across a given range of motion
For example, a chronically tight levator scapulae can pull your scapula into an elevated position with an anterior (forward) tilt that leads to nerve or bursa impingement between the head of the humerus and your acromion processes when trying to perform overhead motions, because the rest of the kinematic chain has to compensate for the locked-in levator scapulae. Over time, you can also start to develop chronically faulty motor patterns because your body is used to activating muscles in a certain manner despite the initial injury subsiding. Hence why some dudes - like me - can go for years kicking their can of asymptomatic imbalances down the road til something snaps for real and the house of cards collapses, because the strong points you used to rely on have been undermined by a litany of issues you turned a blind eye towards. The reason why I'm being exhaustive with this post is partially because I wanna stress the importance of keeping an inquiring mindset on prehab issues, as well as inventoring the knowledge I've accumulated thus far to see whether I can transfer it to someone else.
Finally, an additional, VERY useful layer of perspective can be found in Thomas Myers' "Anatomy Trains" and the concept of myofascial networks. In a nutshell, the neatly separated muscles you see on an anatomical chart are in reality interconnected by a web of myofascial sheaths that influence eachother a lot more than previously thought. A few images of the concept will show how muscular imblances can result in symptoms in remote areas of the body.
Having the concept running like a background process as you're assessing yourself is immensely useful in forming a complete understanding of how your body works and why injuries and dysfunctional movement patterns occur. The book named above is pricey but IMO well worth it.
That was quite a brick of a read I just gave you, but given that it's basically a summary of a decade of anatomical interest condensed into a couple of dense pages, it should be. If there's anything you're wondering about the process, just ask.
