Lena Dunham isn't exactly the epitome of physical fitness. Yet the writer and star of HBO's Girls shared her enthusiasm for AcroYoga in a March 12 interview with David Letterman. Referring to a photo of herself balancing upside down on Koha Yoga teacher Whakapaingia (“Whaka” for short), Dunham educated the now-retired late show host. “That is called AcroYoga. Believe it or not, that takes a lot of core strength. I say this with a lot of self-love: Behind the wall of fat, my stomach muscles are doing a lot. If I was this adventuresome in my early 20s, I would've had a better time in the boyfriend department.”