I did an offseason fitness program with my swing coach. He's TPI certified so I went through a series of those exercises and monthly screenings.
Here are my results:
Lost 15 pounds! New golf attire!
Added 5mph on my swing speed. More distance!
Added half a club to a club to my iron distances!
No longer sore after playing a full round.
Had to get my irons adjusted back to standard lie now that my posture is better.
My scores haven't improved much as I need to get used to the new distance and get my feeling back with my putter.
TL;DR - Did offseason training, lost weight and added distance. Get fit in more ways than just your clubs.