I'm a plus sized rider. 5"3" and 230 lbs
This is compounded by being VERY out of shape, not riding for a few years due to weight and fears (from past wrecks). I have two good geldings now. Chip is 14.2H and Nick is 15H.
My problem is mounting. I don't mind using a mounting block, it's just sometimes when I put my left foot into the stirrup and tell my right leg to lift over the horse, it doesn't do anything. Almost like there is no muscle there. I do eventually get on and thank goodness both my boys are patient about this. My right leg scrrrrrrappppppes over their butt, then settles in.
Once riding my previous years of training take over and I do use every leg muscle I have. Of course, they all hurt the next day
I'm hoping with time, those leg muscles will firm up.