In Showdown Town, Boggy own's a gym he bought from Mr. Fit. His wife, Mrs. Boggy is mentioned to have forced him to do this to make money and refuses to feed him until he raises enough.
At Boggy's gym, you can upgrade your Speed, in order to make Banjo run faster on foot, Strength, allowing Banjo to deal more damage to Enemies on foot, and Stamina, allowing Banjo to take more damage without getting knocked out. You can only upgrade each three times, and Boggy refuses to upgrade it any further because "you'll look freakish".