My feeder (wife) has been very fit for the last several years - she is a gym rat who ran a few marathons, that sort of thing. For the last few years she has fattened me up to my current size. (I've written the full story in the story section here on FF - "My gaining story - reversal of roles" and in "My gaining story vol. 2" if you're interested.)
We've both loved the contrast - her getting stronger and more fit, me getting fatter and weaker.
Last month she was in Calgary, and was inspired by something that I think will take this comparison to the next level - she wants to start training for the Canada's Strongest Woman competition next year!
She saw it, and was so inspired by the women competing and now she wants to do it! So I think the contrast between fitty and fatty is going to get a little more pronounced!