For me, the best way to get in shape for dinghy sailing in higher winds is to sail in as much wind as you can during the summer and early fall months. By this time in August I am usually getting to my low body weight for the year.
Along with trimming down, I find as I age I am losing some weight each year and some of my muscle mass is going with it (despite some gym work). My last physical checked out fine; low blood pressure and no issues found but I am losing body ballast for sailing in wind! Here is my latest rig to balance this out some when I don't have crew up front! Cheers