Seems to be from around Berlin around 1900. So probably coming from FKK http://en.wikipedia.org/wiki... and the fashion of Walden inspired back-to-nature communes at the time. I'm also reminded of Rudolf Steiner and Blavatsky.
What we call Yoga nowadays was also heavily formed by 19th century health and fitness practices http://uddari.wordpress.com/2011... (blog text of TLS article that's behind a paywall)
You may be interested in the book that that article is a review of Mark Singleton - Yoga body
You shouldn't let people bully you like that.