Elbow falling behind the guitar

As the title says, my elbow for some unknown reason now wants to fall behind the guitar and is causing mega issues with trying to get the forearm angle for the supinated wrist setup. I’ve been playing guitar for near on 10 years and this never used to be a problem. but it’s like I’ve forgotten how to hold the guitar and it’s doing my swede in so i’m wondering how you lot fixed this issue.

FYI the guitars I use are a les Paul and a ltd superstrat so don’t have any contours.

I think this might be one of those “picture is worth a thousand words” situations. Is the guitar touching your torso in the same place it always has?

Yup, that would be very beneficial.

Without seeing what’s happening, guessing entirely based on your description…

You’re holding the guitar pretty “flat” across your torso (guitar perpendicular to your legs if that’s easier to visualize… in line with your pelvis) and you’re holding your elbow in the correct place by engaging your deltoid. Now you’re relaxing your deltoid (or it’s tired), and the elbow is going “behind” the guitar. Again, this is a total guess, without any pics lol.

The fix, if this were the case, would be to hold your guitar more diagonal to your torso / pelvis, so your shoulder doesn’t have to compensate and would be relaxed.