He is/was a runner. Could explain the body/build. Found this article from 2014:
https://www.runnersworld.com/runners-stories/a20852230/a-running-conversation-with-john-podesta/
Excerpt:
I met the veteran politico one wet morning at the Hatch Memorial Shell on Boston's Esplanade. Podesta was in town for a board meeting. He has a slim build and was wearing a T-shirt that read "Think Progress." We settled into a comfortable nine-minute-per-mile pace for six soggy miles along the Charles River. Podesta strode with a smooth, light gait, snot-rocketed like a boss, and unspooled colorful anecdotes without gasping for breath, his words coated with a Chicago accent.
Caleb Daniloff: When did you start seriously running?
John Podesta: I remember running as a kid and coming back to running in my late 30s. By that time, I had three kids and my basic exercise was chasing them around. I went to my high school track and ran a mile. I was completely exhausted and thought, This is bad. I kept at it. But I really got serious in my late 40s. I ran my first marathon when I was 52 (4:23, San Diego Rock 'n' Roll Marathon). Now, I average a half dozen races a year, mostly 10-K, 10-mile, or half-marathon. My last marathon was in 2010 (4:34, Rome Marathon). I do 25 miles a week, five to six days a week, even while traveling.