I’m sure cognizant of the differences in my own fitness make to my enjoyment afield. To the point that some years I specifically train for it. We condition dogs preseason. Why wouldn’t we condition ourselves?
But having said that, like Ted, I pick the gun weight/ gauge/ load suitable for what I’m hunting.
If I’m hunting pheasant or sharptails on the Great Plains I find that a 6 3/4 pound gun, usually 12 or 16 ga, is about perfect. If it’s ruffies or woodcock that I’m walking through the forest for and hunting behind a setter then 5 3/4 to 6 1/4 seems about right.