I got nothing on fitness, but lots of others...
Adam Buxton, Richard Herring, Scroobius Pip are probably the premier UK interview based podcasts, imo. Marc Maron's WTF, and Dad Shepard's Armchair Expert are great USA ones.
Films to be Buried With, by Brett Goldstein is a sort of Desert Island Discs for movies, and is really good.
The Parapod, now ended after 3 seasons but with a film on the way, is a hilarious look at the paranormal. I've listened to most of it 2 or 3 times.
Guys We ****** is a fun sex discussion podcast. They've gone behind a paywall now, and the show had dropped off in the last year or so before that (the openness and honesty of the two hosts being constricted by the increasing fame of the show), but it's worth tuning in from the beginning.
Reply All, Love + Radio, and Radiolab are all fantastic journalistic looks at aspects of science, culture and humanity. All worth a look.
Others I listen to a bit include id10t, Holly Randall (she's a porn photographer), David Tennant, Alec Baldwin, Chris D'elia, Hardcore Listing, Dan le Sac.....
Oh, and both of Jon Ronson's series are well worth a listen.