Do i lack straight arm strength or is it a mobility/flexibility issue?

Good day Gymnasts!
So recently i have been training a lot of exercises like skin the cat, tuck front lever, and human flag progressions all with arms locked and straight of course. The problem is that i experience kinda 'knacks' in my elbows en shoulders. It feels like it's not flexible enough but i have to give some additional information though. I have never trained straight arm strength properly, so maybe that's the problem. However i do not feel limitation in my muscles, but really in the shoulder and elbow joints. 
I do not continue to train like this if i feel that my elbow/shoulder joints can't handle the load (it doesnt hurt but feels like a 'knack'). I really hope someone can tell me more about the cause of this problem. I always stretch my entire body in a few minutes before my workout.

Thanks alot!

6 minutes ago, Aran Van Dinteren said:

 i do not feel limitation in my muscles, but really in the shoulder and elbow joints. 

Sounds like an injury waiting to happen. Pre-stretching before your workouts won't do a thing, if your joints cannot handle the loads from your training.
Connective tissues at the attachment sites: ligaments, tendons.... is where clicks > "knacks" > boom > slap > torn.

Be careful. Train smart. Even when you do, sh*t happens. 

Straight arm strength must be developed progressively. There are lower level straight arm exercises that should be developed first before front lever and human flag progressions. Like was already mentioned, Foundation will be your best guide for this. 

6 hours ago, Eva Pelegrin said:

Sounds like an injury waiting to happen. Pre-stretching before your workouts won't do a thing, if your joints cannot handle the loads from your training.
Connective tissues at the attachment sites: ligaments, tendons.... is where clicks > "knacks" > boom > slap > torn.

Be careful. Train smart. Even when you do, sh*t happens. 

Well summarised. 

Foundation one will address these issues.

Thanks for the information all, i know what to do next (-;