I can help (multiple spine issues).

I was big, now im just a little big, but can do the same weight for the longest. Now that it's been a few years of compression I am noticing fatigue doing 'common' things like holding arms and shoulders up too long - yet can still do the heavy weight. So - it's complicated! My first spine doc visit schedule this week. But more or less the size goes real fast, and the strength far slower.