Hibiya Club

Found an article in the evening Nikkei about "horizontal bar oyajis".
These oyajis, or senior men are nearby office workers and bureaucrats, all members of the "Hibiya Club".
A Japanese page with pictures
These horizontal bar maniacs gather in one corner of Hibiya Park and practice their techniques, many of them naked from the waist up even in winter. The Hibiya Club is said to have began during World War II. One of the oldest members Mr. Ebihara, 62, says he has been coming here for over 36 years (the macho man in this page).
Some members do the giant swing like in the American Express commercial.

Anyone can join in for free. Many don't even know each other's names.
Members usually come around 7:30~9:00 a.m. & 12:00~13:00p.m.