Forearms going weak above the head

[mrwatchins]

When doing pulling exercises with hands above my head (cable pulldowns, pull-ups etc), I get burning sensation in my forearms, like I was dead hanging for on hour, even when I'm doing only second set. I tried different handles (wide, narrow, neutral), I also use wrist grips, no difference - when I start working out I feel like the blood is not flowing into my hands. I don't have that issue when doing back exercises with hands below head level, like cable rows. I've been to physiotherapist, he told me it's "elevated first rib", he worked on my chest near the collarbone but it changed nothing.

Does anyone have any idea what can I do?

 

[Thrawn]

No idea but I'll throw you some questions people may ask you.
What's your current list of medications
BP
Labs
Any current medical issues.
Do you supplement with grapefruit juice or St John's Wort?
How long has this issue been happening?
You age, weight, height

 

[mrwatchins]

I don't use currently any meds or supplements. I haven't been to any specialist other than the physiotherapist.
I had this issue for at least past 3 years (but I didn't really realize that, I just thought that I had weak lats)
30 years old, 82kg, 175cm