So! You already know the problem. Quit shooting BEFORE you get tired out. Shooting when you're tired does nothing but cause you to form bad habits and reinforce the bad habits you've already got. Not to mention the likelihood of injuring already inflamed joints.

Physical limitations suck! But those of us that have 'em need to work within what abilities we DO have. I've had to cut way back on the amount of shooting I do because of arthritis. I hate it, but there it is.